Theory Word_Lemmas
section "Lemmas with Generic Word Length"
theory Word_Lemmas
imports
Type_Syntax
Signed_Division_Word
Signed_Words
More_Word
Most_significant_bit
Enumeration_Word
Aligned
Bit_Shifts_Infix_Syntax
Boolean_Inequalities
Word_EqI
begin
context
includes bit_operations_syntax
begin
lemma word_max_le_or:
"max x y ≤ x OR y" for x :: "'a::len word"
by (simp add: word_bool_le_funs)
lemma word_and_le_min:
"x AND y ≤ min x y" for x :: "'a::len word"
by (simp add: word_bool_le_funs)
lemma word_not_le_eq:
"(NOT x ≤ y) = (NOT y ≤ x)" for x :: "'a::len word"
by transfer (auto simp: take_bit_not_eq_mask_diff)
lemma word_not_le_not_eq[simp]:
"(NOT y ≤ NOT x) = (x ≤ y)" for x :: "'a::len word"
by (subst word_not_le_eq) simp
lemma not_min_eq:
"NOT (min x y) = max (NOT x) (NOT y)" for x :: "'a::len word"
unfolding min_def max_def
by auto
lemma not_max_eq:
"NOT (max x y) = min (NOT x) (NOT y)" for x :: "'a::len word"
unfolding min_def max_def
by auto
lemma ucast_le_ucast_eq:
fixes x y :: "'a::len word"
assumes x: "x < 2 ^ n"
assumes y: "y < 2 ^ n"
assumes n: "n = LENGTH('b::len)"
shows "(UCAST('a → 'b) x ≤ UCAST('a → 'b) y) = (x ≤ y)"
apply (rule iffI)
apply (cases "LENGTH('b) < LENGTH('a)")
apply (subst less_mask_eq[OF x, symmetric])
apply (subst less_mask_eq[OF y, symmetric])
apply (unfold n)
apply (subst ucast_ucast_mask[symmetric])+
apply (simp add: ucast_le_ucast)+
apply (erule ucast_mono_le[OF _ y[unfolded n]])
done
lemma ucast_zero_is_aligned:
‹is_aligned w n› if ‹UCAST('a::len → 'b::len) w = 0› ‹n ≤ LENGTH('b)›
proof (rule is_aligned_bitI)
fix q
assume ‹q < n›
moreover have ‹bit (UCAST('a::len → 'b::len) w) q = bit 0 q›
using that by simp
with ‹q < n› ‹n ≤ LENGTH('b)› show ‹¬ bit w q›
by (simp add: bit_simps)
qed
lemma unat_ucast_eq_unat_and_mask:
"unat (UCAST('b::len → 'a::len) w) = unat (w AND mask LENGTH('a))"
apply (simp flip: take_bit_eq_mask)
apply transfer
apply (simp add: ac_simps)
done
lemma le_max_word_ucast_id:
‹UCAST('b → 'a) (UCAST('a → 'b) x) = x›
if ‹x ≤ UCAST('b::len → 'a) (- 1)›
for x :: ‹'a::len word›
proof -
from that have a1: ‹x ≤ word_of_int (uint (word_of_int (2 ^ LENGTH('b) - 1) :: 'b word))›
by (simp add: of_int_mask_eq)
have f2: "((∃i ia. (0::int) ≤ i ∧ ¬ 0 ≤ i + - 1 * ia ∧ i mod ia ≠ i) ∨
¬ (0::int) ≤ - 1 + 2 ^ LENGTH('b) ∨ (0::int) ≤ - 1 + 2 ^ LENGTH('b) + - 1 * 2 ^ LENGTH('b) ∨
(- (1::int) + 2 ^ LENGTH('b)) mod 2 ^ LENGTH('b) =
- 1 + 2 ^ LENGTH('b)) = ((∃i ia. (0::int) ≤ i ∧ ¬ 0 ≤ i + - 1 * ia ∧ i mod ia ≠ i) ∨
¬ (1::int) ≤ 2 ^ LENGTH('b) ∨
2 ^ LENGTH('b) + - (1::int) * ((- 1 + 2 ^ LENGTH('b)) mod 2 ^ LENGTH('b)) = 1)"
by force
have f3: "∀i ia. ¬ (0::int) ≤ i ∨ 0 ≤ i + - 1 * ia ∨ i mod ia = i"
using mod_pos_pos_trivial by force
have "(1::int) ≤ 2 ^ LENGTH('b)"
by simp
then have "2 ^ LENGTH('b) + - (1::int) * ((- 1 + 2 ^ LENGTH('b)) mod 2 ^ len_of TYPE ('b)) = 1"
using f3 f2 by blast
then have f4: "- (1::int) + 2 ^ LENGTH('b) = (- 1 + 2 ^ LENGTH('b)) mod 2 ^ LENGTH('b)"
by linarith
have f5: "x ≤ word_of_int (uint (word_of_int (- 1 + 2 ^ LENGTH('b))::'b word))"
using a1 by force
have f6: "2 ^ LENGTH('b) + - (1::int) = - 1 + 2 ^ LENGTH('b)"
by force
have f7: "- (1::int) * 1 = - 1"
by auto
have "∀x0 x1. (x1::int) - x0 = x1 + - 1 * x0"
by force
then have "x ≤ 2 ^ LENGTH('b) - 1"
using f7 f6 f5 f4 by (metis uint_word_of_int wi_homs(2) word_arith_wis(8) word_of_int_2p)
then have ‹uint x ≤ uint (2 ^ LENGTH('b) - (1 :: 'a word))›
by (simp add: word_le_def)
then have ‹uint x ≤ 2 ^ LENGTH('b) - 1›
by (simp add: uint_word_ariths)
(metis ‹1 ≤ 2 ^ LENGTH('b)› ‹uint x ≤ uint (2 ^ LENGTH('b) - 1)› linorder_not_less lt2p_lem uint_1 uint_minus_simple_alt uint_power_lower word_le_def zle_diff1_eq)
then show ?thesis
apply (simp add: unsigned_ucast_eq take_bit_word_eq_self_iff)
apply (meson ‹x ≤ 2 ^ LENGTH('b) - 1› not_le word_less_sub_le)
done
qed
lemma uint_shiftr_eq:
‹uint (w >> n) = uint w div 2 ^ n›
by word_eqI
lemma bit_shiftl_word_iff [bit_simps]:
‹bit (w << m) n ⟷ m ≤ n ∧ n < LENGTH('a) ∧ bit w (n - m)›
for w :: ‹'a::len word›
by (simp add: bit_simps)
lemma bit_shiftr_word_iff:
‹bit (w >> m) n ⟷ bit w (m + n)›
for w :: ‹'a::len word›
by (simp add: bit_simps)
lemma uint_sshiftr_eq:
‹uint (w >>> n) = take_bit LENGTH('a) (sint w div 2 ^ n)›
for w :: ‹'a::len word›
by (word_eqI_solve dest: test_bit_lenD)
lemma sshiftr_n1: "-1 >>> n = -1"
by (simp add: sshiftr_def)
lemma nth_sshiftr:
"bit (w >>> m) n = (n < size w ∧ (if n + m ≥ size w then bit w (size w - 1) else bit w (n + m)))"
apply (auto simp add: bit_simps word_size ac_simps not_less)
apply (meson bit_imp_le_length bit_shiftr_word_iff leD)
done
lemma sshiftr_numeral:
‹(numeral k >>> numeral n :: 'a::len word) =
word_of_int (signed_take_bit (LENGTH('a) - 1) (numeral k) >> numeral n)›
using signed_drop_bit_word_numeral [of n k] by (simp add: sshiftr_def shiftr_def)
lemma sshiftr_div_2n: "sint (w >>> n) = sint w div 2 ^ n"
by word_eqI (cases ‹n < LENGTH('a)›; fastforce simp: le_diff_conv2)
lemma mask_eq:
‹mask n = (1 << n) - (1 :: 'a::len word)›
by (simp add: mask_eq_exp_minus_1 shiftl_def)
lemma nth_shiftl': "bit (w << m) n ⟷ n < size w ∧ n >= m ∧ bit w (n - m)"
for w :: "'a::len word"
by (simp add: bit_simps word_size ac_simps)
lemmas nth_shiftl = nth_shiftl' [unfolded word_size]
lemma nth_shiftr: "bit (w >> m) n = bit w (n + m)"
for w :: "'a::len word"
by (simp add: bit_simps ac_simps)
lemma shiftr_div_2n: "uint (shiftr w n) = uint w div 2 ^ n"
by (fact uint_shiftr_eq)
lemma shiftl_rev: "shiftl w n = word_reverse (shiftr (word_reverse w) n)"
by word_eqI_solve
lemma rev_shiftl: "word_reverse w << n = word_reverse (w >> n)"
by (simp add: shiftl_rev)
lemma shiftr_rev: "w >> n = word_reverse (word_reverse w << n)"
by (simp add: rev_shiftl)
lemma rev_shiftr: "word_reverse w >> n = word_reverse (w << n)"
by (simp add: shiftr_rev)
lemmas ucast_up =
rc1 [simplified rev_shiftr [symmetric] revcast_ucast [symmetric]]
lemmas ucast_down =
rc2 [simplified rev_shiftr revcast_ucast [symmetric]]
lemma shiftl_zero_size: "size x ≤ n ⟹ x << n = 0"
for x :: "'a::len word"
by (simp add: shiftl_def word_size)
lemma shiftl_t2n: "shiftl w n = 2 ^ n * w"
for w :: "'a::len word"
by (simp add: shiftl_def push_bit_eq_mult)
lemma word_shift_by_2:
"x * 4 = (x::'a::len word) << 2"
by (simp add: shiftl_t2n)
lemma word_shift_by_3:
"x * 8 = (x::'a::len word) << 3"
by (simp add: shiftl_t2n)
lemma slice_shiftr: "slice n w = ucast (w >> n)"
by word_eqI (cases ‹n ≤ LENGTH('b)›; fastforce simp: ac_simps dest: bit_imp_le_length)
lemma shiftr_zero_size: "size x ≤ n ⟹ x >> n = 0"
for x :: "'a :: len word"
by word_eqI
lemma shiftr_x_0 [simp]: "x >> 0 = x"
for x :: "'a::len word"
by (simp add: shiftr_def)
lemma shiftl_x_0 [simp]: "x << 0 = x"
for x :: "'a::len word"
by (simp add: shiftl_def)
lemmas shiftl0 = shiftl_x_0
lemma shiftr_1 [simp]: "(1::'a::len word) >> n = (if n = 0 then 1 else 0)"
by (simp add: shiftr_def)
lemma and_not_mask:
"w AND NOT (mask n) = (w >> n) << n"
for w :: ‹'a::len word›
by word_eqI_solve
lemma and_mask:
"w AND mask n = (w << (size w - n)) >> (size w - n)"
for w :: ‹'a::len word›
by word_eqI_solve
lemma shiftr_div_2n_w: "w >> n = w div (2^n :: 'a :: len word)"
by (fact shiftr_eq_div)
lemma le_shiftr:
"u ≤ v ⟹ u >> (n :: nat) ≤ (v :: 'a :: len word) >> n"
apply (unfold shiftr_def)
apply transfer
apply (simp add: take_bit_drop_bit)
apply (simp add: drop_bit_eq_div zdiv_mono1)
done
lemma le_shiftr':
"⟦ u >> n ≤ v >> n ; u >> n ≠ v >> n ⟧ ⟹ (u::'a::len word) ≤ v"
by (metis le_cases le_shiftr verit_la_disequality)
lemma shiftr_mask_le:
"n <= m ⟹ mask n >> m = (0 :: 'a::len word)"
by word_eqI
lemma shiftr_mask [simp]:
‹mask m >> m = (0::'a::len word)›
by (rule shiftr_mask_le) simp
lemma le_mask_iff:
"(w ≤ mask n) = (w >> n = 0)"
for w :: ‹'a::len word›
apply safe
apply (rule word_le_0_iff [THEN iffD1])
apply (rule xtrans(3))
apply (erule_tac [2] le_shiftr)
apply simp
apply (rule word_leI)
apply (rename_tac n')
apply (drule_tac x = "n' - n" in word_eqD)
apply (simp add : nth_shiftr word_size bit_simps)
apply (case_tac "n <= n'")
by auto
lemma and_mask_eq_iff_shiftr_0:
"(w AND mask n = w) = (w >> n = 0)"
for w :: ‹'a::len word›
by (simp flip: take_bit_eq_mask add: shiftr_def take_bit_eq_self_iff_drop_bit_eq_0)
lemma mask_shiftl_decompose:
"mask m << n = mask (m + n) AND NOT (mask n :: 'a::len word)"
by word_eqI_solve
lemma shiftl_over_and_dist:
fixes a::"'a::len word"
shows "(a AND b) << c = (a << c) AND (b << c)"
by (unfold shiftl_def) (fact push_bit_and)
lemma shiftr_over_and_dist:
fixes a::"'a::len word"
shows "a AND b >> c = (a >> c) AND (b >> c)"
by (unfold shiftr_def) (fact drop_bit_and)
lemma sshiftr_over_and_dist:
fixes a::"'a::len word"
shows "a AND b >>> c = (a >>> c) AND (b >>> c)"
by word_eqI
lemma shiftl_over_or_dist:
fixes a::"'a::len word"
shows "a OR b << c = (a << c) OR (b << c)"
by (unfold shiftl_def) (fact push_bit_or)
lemma shiftr_over_or_dist:
fixes a::"'a::len word"
shows "a OR b >> c = (a >> c) OR (b >> c)"
by (unfold shiftr_def) (fact drop_bit_or)
lemma sshiftr_over_or_dist:
fixes a::"'a::len word"
shows "a OR b >>> c = (a >>> c) OR (b >>> c)"
by word_eqI
lemmas shift_over_ao_dists =
shiftl_over_or_dist shiftr_over_or_dist
sshiftr_over_or_dist shiftl_over_and_dist
shiftr_over_and_dist sshiftr_over_and_dist
lemma shiftl_shiftl:
fixes a::"'a::len word"
shows "a << b << c = a << (b + c)"
by (word_eqI_solve simp: add.commute add.left_commute)
lemma shiftr_shiftr:
fixes a::"'a::len word"
shows "a >> b >> c = a >> (b + c)"
by word_eqI (simp add: add.left_commute add.commute)
lemma shiftl_shiftr1:
fixes a::"'a::len word"
shows "c ≤ b ⟹ a << b >> c = a AND (mask (size a - b)) << (b - c)"
by word_eqI (auto simp: ac_simps)
lemma shiftl_shiftr2:
fixes a::"'a::len word"
shows "b < c ⟹ a << b >> c = (a >> (c - b)) AND (mask (size a - c))"
by word_eqI_solve
lemma shiftr_shiftl1:
fixes a::"'a::len word"
shows "c ≤ b ⟹ a >> b << c = (a >> (b - c)) AND (NOT (mask c))"
by word_eqI_solve
lemma shiftr_shiftl2:
fixes a::"'a::len word"
shows "b < c ⟹ a >> b << c = (a << (c - b)) AND (NOT (mask c))"
by word_eqI (auto simp: ac_simps)
lemmas multi_shift_simps =
shiftl_shiftl shiftr_shiftr
shiftl_shiftr1 shiftl_shiftr2
shiftr_shiftl1 shiftr_shiftl2
lemma shiftr_mask2:
"n ≤ LENGTH('a) ⟹ (mask n >> m :: ('a :: len) word) = mask (n - m)"
by word_eqI_solve
lemma word_shiftl_add_distrib:
fixes x :: "'a :: len word"
shows "(x + y) << n = (x << n) + (y << n)"
by (simp add: shiftl_t2n ring_distribs)
lemma mask_shift:
"(x AND NOT (mask y)) >> y = x >> y"
for x :: ‹'a::len word›
by word_eqI
lemma shiftr_div_2n':
"unat (w >> n) = unat w div 2 ^ n"
by word_eqI
lemma shiftl_shiftr_id:
"⟦ n < LENGTH('a); x < 2 ^ (LENGTH('a) - n) ⟧ ⟹ x << n >> n = (x::'a::len word)"
by word_eqI (metis add.commute less_diff_conv)
lemma ucast_shiftl_eq_0:
fixes w :: "'a :: len word"
shows "⟦ n ≥ LENGTH('b) ⟧ ⟹ ucast (w << n) = (0 :: 'b :: len word)"
by (transfer fixing: n) (simp add: take_bit_push_bit)
lemma word_shift_nonzero:
"⟦ (x::'a::len word) ≤ 2 ^ m; m + n < LENGTH('a::len); x ≠ 0⟧
⟹ x << n ≠ 0"
apply (simp only: word_neq_0_conv word_less_nat_alt
shiftl_t2n mod_0 unat_word_ariths
unat_power_lower word_le_nat_alt)
apply (subst mod_less)
apply (rule order_le_less_trans)
apply (erule mult_le_mono2)
apply (subst power_add[symmetric])
apply (rule power_strict_increasing)
apply simp
apply simp
apply simp
done
lemma word_shiftr_lt:
fixes w :: "'a::len word"
shows "unat (w >> n) < (2 ^ (LENGTH('a) - n))"
apply (subst shiftr_div_2n')
apply transfer
apply (simp flip: drop_bit_eq_div add: drop_bit_nat_eq drop_bit_take_bit)
done
lemma shiftr_less_t2n':
"⟦ x AND mask (n + m) = x; m < LENGTH('a) ⟧ ⟹ x >> n < 2 ^ m" for x :: "'a :: len word"
apply (simp add: word_size mask_eq_iff_w2p [symmetric] flip: take_bit_eq_mask)
apply transfer
apply (simp add: take_bit_drop_bit ac_simps)
done
lemma shiftr_less_t2n:
"x < 2 ^ (n + m) ⟹ x >> n < 2 ^ m" for x :: "'a :: len word"
apply (rule shiftr_less_t2n')
apply (erule less_mask_eq)
apply (rule ccontr)
apply (simp add: not_less)
apply (subst (asm) p2_eq_0[symmetric])
apply (simp add: power_add)
done
lemma shiftr_eq_0:
"n ≥ LENGTH('a) ⟹ ((w::'a::len word) >> n) = 0"
apply (cut_tac shiftr_less_t2n'[of w n 0], simp)
apply (simp add: mask_eq_iff)
apply (simp add: lt2p_lem)
apply simp
done
lemma shiftl_less_t2n:
fixes x :: "'a :: len word"
shows "⟦ x < (2 ^ (m - n)); m < LENGTH('a) ⟧ ⟹ (x << n) < 2 ^ m"
apply (simp add: word_size mask_eq_iff_w2p [symmetric] flip: take_bit_eq_mask)
apply transfer
apply (simp add: take_bit_push_bit)
done
lemma shiftl_less_t2n':
"(x::'a::len word) < 2 ^ m ⟹ m+n < LENGTH('a) ⟹ x << n < 2 ^ (m + n)"
by (rule shiftl_less_t2n) simp_all
lemma scast_bit_test [simp]:
"scast ((1 :: 'a::len signed word) << n) = (1 :: 'a word) << n"
by word_eqI
lemma signed_shift_guard_to_word:
‹unat x * 2 ^ y < 2 ^ n ⟷ x = 0 ∨ x < 1 << n >> y›
if ‹n < LENGTH('a)› ‹0 < n›
for x :: ‹'a::len word›
proof (cases ‹x = 0›)
case True
then show ?thesis
by simp
next
case False
then have ‹unat x ≠ 0›
by (simp add: unat_eq_0)
then have ‹unat x ≥ 1›
by simp
show ?thesis
proof (cases ‹y < n›)
case False
then have ‹n ≤ y›
by simp
then obtain q where ‹y = n + q›
using le_Suc_ex by blast
moreover have ‹(2 :: nat) ^ n >> n + q ≤ 1›
by (simp add: drop_bit_eq_div power_add shiftr_def)
ultimately show ?thesis
using ‹x ≠ 0› ‹unat x ≥ 1› ‹n < LENGTH('a)›
by (simp add: power_add not_less word_le_nat_alt unat_drop_bit_eq shiftr_def shiftl_def)
next
case True
with that have ‹y < LENGTH('a)›
by simp
show ?thesis
proof (cases ‹2 ^ n = unat x * 2 ^ y›)
case True
moreover have ‹unat x * 2 ^ y < 2 ^ LENGTH('a)›
using ‹n < LENGTH('a)› by (simp flip: True)
moreover have ‹(word_of_nat (2 ^ n) :: 'a word) = word_of_nat (unat x * 2 ^ y)›
using True by simp
then have ‹2 ^ n = x * 2 ^ y›
by simp
ultimately show ?thesis
using ‹y < LENGTH('a)›
by (auto simp add: drop_bit_eq_div word_less_nat_alt unat_div unat_word_ariths
shiftr_def shiftl_def)
next
case False
with ‹y < n› have *: ‹unat x ≠ 2 ^ n div 2 ^ y›
by (auto simp flip: power_sub power_add)
have ‹unat x * 2 ^ y < 2 ^ n ⟷ unat x * 2 ^ y ≤ 2 ^ n›
using False by (simp add: less_le)
also have ‹… ⟷ unat x ≤ 2 ^ n div 2 ^ y›
by (simp add: less_eq_div_iff_mult_less_eq)
also have ‹… ⟷ unat x < 2 ^ n div 2 ^ y›
using * by (simp add: less_le)
finally show ?thesis
using that ‹x ≠ 0› by (simp flip: push_bit_eq_mult drop_bit_eq_div
add: shiftr_def shiftl_def unat_drop_bit_eq word_less_iff_unsigned [where ?'a = nat])
qed
qed
qed
lemma shiftr_not_mask_0:
"n+m ≥ LENGTH('a :: len) ⟹ ((w::'a::len word) >> n) AND NOT (mask m) = 0"
by word_eqI
lemma shiftl_mask_is_0[simp]:
"(x << n) AND mask n = 0"
for x :: ‹'a::len word›
by (simp flip: take_bit_eq_mask add: take_bit_push_bit shiftl_def)
lemma rshift_sub_mask_eq:
"(a >> (size a - b)) AND mask b = a >> (size a - b)"
for a :: ‹'a::len word›
using shiftl_shiftr2[where a=a and b=0 and c="size a - b"]
apply (cases "b < size a")
apply simp
apply (simp add: linorder_not_less mask_eq_decr_exp word_size
p2_eq_0[THEN iffD2])
done
lemma shiftl_shiftr3:
"b ≤ c ⟹ a << b >> c = (a >> c - b) AND mask (size a - c)"
for a :: ‹'a::len word›
apply (cases "b = c")
apply (simp add: shiftl_shiftr1)
apply (simp add: shiftl_shiftr2)
done
lemma and_mask_shiftr_comm:
"m ≤ size w ⟹ (w AND mask m) >> n = (w >> n) AND mask (m-n)"
for w :: ‹'a::len word›
by (simp add: and_mask shiftr_shiftr) (simp add: word_size shiftl_shiftr3)
lemma and_mask_shiftl_comm:
"m+n ≤ size w ⟹ (w AND mask m) << n = (w << n) AND mask (m+n)"
for w :: ‹'a::len word›
by (simp add: and_mask word_size shiftl_shiftl) (simp add: shiftl_shiftr1)
lemma le_mask_shiftl_le_mask: "s = m + n ⟹ x ≤ mask n ⟹ x << m ≤ mask s"
for x :: ‹'a::len word›
by (simp add: le_mask_iff shiftl_shiftr3)
lemma word_and_1_shiftl:
"x AND (1 << n) = (if bit x n then (1 << n) else 0)" for x :: "'a :: len word"
by word_eqI_solve
lemmas word_and_1_shiftls'
= word_and_1_shiftl[where n=0]
word_and_1_shiftl[where n=1]
word_and_1_shiftl[where n=2]
lemmas word_and_1_shiftls = word_and_1_shiftls' [simplified]
lemma word_and_mask_shiftl:
"x AND (mask n << m) = ((x >> m) AND mask n) << m"
for x :: ‹'a::len word›
by word_eqI_solve
lemma shift_times_fold:
"(x :: 'a :: len word) * (2 ^ n) << m = x << (m + n)"
by (simp add: shiftl_t2n ac_simps power_add)
lemma of_bool_nth:
"of_bool (bit x v) = (x >> v) AND 1"
for x :: ‹'a::len word›
by (simp add: bit_iff_odd_drop_bit word_and_1 shiftr_def)
lemma shiftr_mask_eq:
"(x >> n) AND mask (size x - n) = x >> n" for x :: "'a :: len word"
by (word_eqI_solve dest: test_bit_lenD)
lemma shiftr_mask_eq':
"m = (size x - n) ⟹ (x >> n) AND mask m = x >> n" for x :: "'a :: len word"
by (simp add: shiftr_mask_eq)
lemma and_eq_0_is_nth:
fixes x :: "'a :: len word"
shows "y = 1 << n ⟹ ((x AND y) = 0) = (¬ (bit x n))"
by (simp add: and_exp_eq_0_iff_not_bit shiftl_def)
lemma word_shift_zero:
"⟦ x << n = 0; x ≤ 2^m; m + n < LENGTH('a)⟧ ⟹ (x::'a::len word) = 0"
apply (rule ccontr)
apply (drule (2) word_shift_nonzero)
apply simp
done
lemma mask_shift_and_negate[simp]:"(w AND mask n << m) AND NOT (mask n << m) = 0"
for w :: ‹'a::len word›
by word_eqI
lemma bitfield_op_twice:
"(x AND NOT (mask n << m) OR ((y AND mask n) << m)) AND NOT (mask n << m) = x AND NOT (mask n << m)"
for x :: ‹'a::len word›
by word_eqI_solve
lemma bitfield_op_twice'':
"⟦NOT a = b << c; ∃x. b = mask x⟧ ⟹ (x AND a OR (y AND b << c)) AND a = x AND a"
for a b :: ‹'a::len word›
by word_eqI_solve
lemma shiftr1_unfold: "x div 2 = x >> 1"
by (simp add: drop_bit_eq_div shiftr_def)
lemma shiftr1_is_div_2: "(x::('a::len) word) >> 1 = x div 2"
by (simp add: drop_bit_eq_div shiftr_def)
lemma shiftl1_is_mult: "(x << 1) = (x :: 'a::len word) * 2"
by (metis One_nat_def mult_2 mult_2_right one_add_one
power_0 power_Suc shiftl_t2n)
lemma shiftr1_lt:"x ≠ 0 ⟹ (x::('a::len) word) >> 1 < x"
apply (subst shiftr1_is_div_2)
apply (rule div_less_dividend_word)
apply simp+
done
lemma shiftr1_0_or_1:"(x::('a::len) word) >> 1 = 0 ⟹ x = 0 ∨ x = 1"
apply (subst (asm) shiftr1_is_div_2)
apply (drule word_less_div)
apply (case_tac "LENGTH('a) = 1")
apply (simp add:degenerate_word)
apply (erule disjE)
apply (subgoal_tac "(2::'a word) ≠ 0")
apply simp
apply (rule not_degenerate_imp_2_neq_0)
apply (subgoal_tac "LENGTH('a) ≠ 0")
apply arith
apply simp
apply (rule x_less_2_0_1', simp+)
done
lemma shiftr1_irrelevant_lsb: "bit (x::('a::len) word) 0 ∨ x >> 1 = (x + 1) >> 1"
by (auto simp add: bit_0 shiftr_def drop_bit_Suc ac_simps elim: evenE)
lemma shiftr1_0_imp_only_lsb:"((x::('a::len) word) + 1) >> 1 = 0 ⟹ x = 0 ∨ x + 1 = 0"
by (metis One_nat_def shiftr1_0_or_1 word_less_1 word_overflow)
lemma shiftr1_irrelevant_lsb': "¬ (bit (x::('a::len) word) 0) ⟹ x >> 1 = (x + 1) >> 1"
using shiftr1_irrelevant_lsb [of x] by simp
lemma cast_chunk_assemble_id:
"⟦n = LENGTH('a::len); m = LENGTH('b::len); n * 2 = m⟧ ⟹
(((ucast ((ucast (x::'b word))::'a word))::'b word) OR (((ucast ((ucast (x >> n))::'a word))::'b word) << n)) = x"
apply (subgoal_tac "((ucast ((ucast (x >> n))::'a word))::'b word) = x >> n")
apply clarsimp
apply (subst and_not_mask[symmetric])
apply (subst ucast_ucast_mask)
apply (subst word_ao_dist2[symmetric])
apply clarsimp
apply (rule ucast_ucast_len)
apply (rule shiftr_less_t2n')
apply (subst and_mask_eq_iff_le_mask)
apply (simp_all add: mask_eq_decr_exp flip: mult_2_right)
apply (metis add_diff_cancel_left' len_gt_0 mult_2_right zero_less_diff)
done
lemma cast_chunk_scast_assemble_id:
"⟦n = LENGTH('a::len); m = LENGTH('b::len); n * 2 = m⟧ ⟹
(((ucast ((scast (x::'b word))::'a word))::'b word) OR
(((ucast ((scast (x >> n))::'a word))::'b word) << n)) = x"
apply (subgoal_tac "((scast x)::'a word) = ((ucast x)::'a word)")
apply (subgoal_tac "((scast (x >> n))::'a word) = ((ucast (x >> n))::'a word)")
apply (simp add:cast_chunk_assemble_id)
apply (subst down_cast_same[symmetric], subst is_down, arith, simp)+
done
lemma unat_shiftr_less_t2n:
fixes x :: "'a :: len word"
shows "unat x < 2 ^ (n + m) ⟹ unat (x >> n) < 2 ^ m"
by (simp add: shiftr_div_2n' power_add mult.commute less_mult_imp_div_less)
lemma ucast_less_shiftl_helper:
"⟦ LENGTH('b) + 2 < LENGTH('a); 2 ^ (LENGTH('b) + 2) ≤ n⟧
⟹ (ucast (x :: 'b::len word) << 2) < (n :: 'a::len word)"
apply (erule order_less_le_trans[rotated])
using ucast_less[where x=x and 'a='a]
apply (simp only: shiftl_t2n field_simps)
apply (rule word_less_power_trans2; simp)
done
lemma NOT_mask_shifted_lenword:
"NOT (mask len << (LENGTH('a) - len) ::'a::len word) = mask (LENGTH('a) - len)"
by word_eqI_solve
lemma shiftr_less:
"(w::'a::len word) < k ⟹ w >> n < k"
by (metis div_le_dividend le_less_trans shiftr_div_2n' unat_arith_simps(2))
lemma word_and_notzeroD:
"w AND w' ≠ 0 ⟹ w ≠ 0 ∧ w' ≠ 0"
by auto
lemma shiftr_le_0:
"unat (w::'a::len word) < 2 ^ n ⟹ w >> n = (0::'a::len word)"
by (auto simp add: take_bit_word_eq_self_iff word_less_nat_alt shiftr_def
simp flip: take_bit_eq_self_iff_drop_bit_eq_0 intro: ccontr)
lemma of_nat_shiftl:
"(of_nat x << n) = (of_nat (x * 2 ^ n) :: ('a::len) word)"
proof -
have "(of_nat x::'a word) << n = of_nat (2 ^ n) * of_nat x"
using shiftl_t2n by (metis word_unat_power)
thus ?thesis by simp
qed
lemma shiftl_1_not_0:
"n < LENGTH('a) ⟹ (1::'a::len word) << n ≠ 0"
by (simp add: shiftl_t2n)
lemma bitmagic_zeroLast_leq_or1Last:
"(a::('a::len) word) AND (mask len << x - len) ≤ a OR mask (y - len)"
by (meson le_word_or2 order_trans word_and_le2)
lemma zero_base_lsb_imp_set_eq_as_bit_operation:
fixes base ::"'a::len word"
assumes valid_prefix: "mask (LENGTH('a) - len) AND base = 0"
shows "(base = NOT (mask (LENGTH('a) - len)) AND a) ⟷
(a ∈ {base .. base OR mask (LENGTH('a) - len)})"
proof
have helper3: "x OR y = x OR y AND NOT x" for x y ::"'a::len word" by (simp add: word_oa_dist2)
from assms show "base = NOT (mask (LENGTH('a) - len)) AND a ⟹
a ∈ {base..base OR mask (LENGTH('a) - len)}"
apply(simp add: word_and_le1)
apply(metis helper3 le_word_or2 word_bw_comms(1) word_bw_comms(2))
done
next
assume "a ∈ {base..base OR mask (LENGTH('a) - len)}"
hence a: "base ≤ a ∧ a ≤ base OR mask (LENGTH('a) - len)" by simp
show "base = NOT (mask (LENGTH('a) - len)) AND a"
proof -
have f2: "∀x⇩0. base AND NOT (mask x⇩0) ≤ a AND NOT (mask x⇩0)"
using a neg_mask_mono_le by blast
have f3: "∀x⇩0. a AND NOT (mask x⇩0) ≤ (base OR mask (LENGTH('a) - len)) AND NOT (mask x⇩0)"
using a neg_mask_mono_le by blast
have f4: "base = base AND NOT (mask (LENGTH('a) - len))"
using valid_prefix by (metis mask_eq_0_eq_x word_bw_comms(1))
hence f5: "∀x⇩6. (base OR x⇩6) AND NOT (mask (LENGTH('a) - len)) =
base OR x⇩6 AND NOT (mask (LENGTH('a) - len))"
using word_ao_dist by (metis)
have f6: "∀x⇩2 x⇩3. a AND NOT (mask x⇩2) ≤ x⇩3 ∨
¬ (base OR mask (LENGTH('a) - len)) AND NOT (mask x⇩2) ≤ x⇩3"
using f3 dual_order.trans by auto
have "base = (base OR mask (LENGTH('a) - len)) AND NOT (mask (LENGTH('a) - len))"
using f5 by auto
hence "base = a AND NOT (mask (LENGTH('a) - len))"
using f2 f4 f6 by (metis eq_iff)
thus "base = NOT (mask (LENGTH('a) - len)) AND a"
by (metis word_bw_comms(1))
qed
qed
lemma of_nat_eq_signed_scast:
"(of_nat x = (y :: ('a::len) signed word))
= (of_nat x = (scast y :: 'a word))"
by (metis scast_of_nat scast_scast_id(2))
lemma word_aligned_add_no_wrap_bounded:
"⟦ w + 2^n ≤ x; w + 2^n ≠ 0; is_aligned w n ⟧ ⟹ (w::'a::len word) < x"
by (blast dest: is_aligned_no_overflow le_less_trans word_leq_le_minus_one)
lemma mask_Suc:
"mask (Suc n) = (2 :: 'a::len word) ^ n + mask n"
by (simp add: mask_eq_decr_exp)
lemma mask_mono:
"sz' ≤ sz ⟹ mask sz' ≤ (mask sz :: 'a::len word)"
by (simp add: le_mask_iff shiftr_mask_le)
lemma aligned_mask_disjoint:
"⟦ is_aligned (a :: 'a :: len word) n; b ≤ mask n ⟧ ⟹ a AND b = 0"
by (metis and_zero_eq is_aligned_mask le_mask_imp_and_mask word_bw_lcs(1))
lemma word_and_or_mask_aligned:
"⟦ is_aligned a n; b ≤ mask n ⟧ ⟹ a + b = a OR b"
by (simp add: aligned_mask_disjoint word_plus_and_or_coroll)
lemma word_and_or_mask_aligned2:
‹is_aligned b n ⟹ a ≤ mask n ⟹ a + b = a OR b›
using word_and_or_mask_aligned [of b n a] by (simp add: ac_simps)
lemma is_aligned_ucastI:
"is_aligned w n ⟹ is_aligned (ucast w) n"
by (simp add: bit_ucast_iff is_aligned_nth)
lemma ucast_le_maskI:
"a ≤ mask n ⟹ UCAST('a::len → 'b::len) a ≤ mask n"
by (metis and_mask_eq_iff_le_mask ucast_and_mask)
lemma ucast_add_mask_aligned:
"⟦ a ≤ mask n; is_aligned b n ⟧ ⟹ UCAST ('a::len → 'b::len) (a + b) = ucast a + ucast b"
by (metis add.commute is_aligned_ucastI ucast_le_maskI ucast_or_distrib word_and_or_mask_aligned)
lemma ucast_shiftl:
"LENGTH('b) ≤ LENGTH ('a) ⟹ UCAST ('a::len → 'b::len) x << n = ucast (x << n)"
by word_eqI_solve
lemma ucast_leq_mask:
"LENGTH('a) ≤ n ⟹ ucast (x::'a::len word) ≤ mask n"
apply (simp add: less_eq_mask_iff_take_bit_eq_self)
apply transfer
apply (simp add: ac_simps)
done
lemma shiftl_inj:
‹x = y›
if ‹x << n = y << n› ‹x ≤ mask (LENGTH('a) - n)› ‹y ≤ mask (LENGTH('a) - n)›
for x y :: ‹'a::len word›
proof (cases ‹n < LENGTH('a)›)
case False
with that show ?thesis
by simp
next
case True
moreover from that have ‹take_bit (LENGTH('a) - n) x = x› ‹take_bit (LENGTH('a) - n) y = y›
by (simp_all add: less_eq_mask_iff_take_bit_eq_self)
ultimately show ?thesis
using ‹x << n = y << n› by (metis diff_less gr_implies_not0 linorder_cases linorder_not_le shiftl_shiftr_id shiftl_x_0 take_bit_word_eq_self_iff)
qed
lemma distinct_word_add_ucast_shift_inj:
‹p' = p ∧ off' = off›
if *: ‹p + (UCAST('a::len → 'b::len) off << n) = p' + (ucast off' << n)›
and ‹is_aligned p n'› ‹is_aligned p' n'› ‹n' = n + LENGTH('a)› ‹n' < LENGTH('b)›
proof -
from ‹n' = n + LENGTH('a)›
have [simp]: ‹n' - n = LENGTH('a)› ‹n + LENGTH('a) = n'›
by simp_all
from ‹is_aligned p n'› obtain q
where p: ‹p = push_bit n' (word_of_nat q)› ‹q < 2 ^ (LENGTH('b) - n')›
by (rule is_alignedE')
from ‹is_aligned p' n'› obtain q'
where p': ‹p' = push_bit n' (word_of_nat q')› ‹q' < 2 ^ (LENGTH('b) - n')›
by (rule is_alignedE')
define m :: nat where ‹m = unat off›
then have off: ‹off = word_of_nat m›
by simp
define m' :: nat where ‹m' = unat off'›
then have off': ‹off' = word_of_nat m'›
by simp
have ‹push_bit n' q + take_bit n' (push_bit n m) < 2 ^ LENGTH('b)›
by (metis id_apply is_aligned_no_wrap''' of_nat_eq_id of_nat_push_bit p(1) p(2) take_bit_nat_eq_self_iff take_bit_nat_less_exp take_bit_push_bit that(2) that(5) unsigned_of_nat)
moreover have ‹push_bit n' q' + take_bit n' (push_bit n m') < 2 ^ LENGTH('b)›
by (metis ‹n' - n = LENGTH('a)› id_apply is_aligned_no_wrap''' m'_def of_nat_eq_id of_nat_push_bit off' p'(1) p'(2) take_bit_nat_eq_self_iff take_bit_push_bit that(3) that(5) unsigned_of_nat)
ultimately have ‹push_bit n' q + take_bit n' (push_bit n m) = push_bit n' q' + take_bit n' (push_bit n m')›
using * by (simp add: p p' off off' push_bit_of_nat push_bit_take_bit word_of_nat_inj unsigned_of_nat shiftl_def flip: of_nat_add)
then have ‹int (push_bit n' q + take_bit n' (push_bit n m))
= int (push_bit n' q' + take_bit n' (push_bit n m'))›
by simp
then have ‹concat_bit n' (int (push_bit n m)) (int q)
= concat_bit n' (int (push_bit n m')) (int q')›
by (simp add: of_nat_push_bit of_nat_take_bit concat_bit_eq)
then show ?thesis
by (simp add: p p' off off' take_bit_of_nat take_bit_push_bit word_of_nat_eq_iff concat_bit_eq_iff)
(simp add: push_bit_eq_mult)
qed
lemma word_upto_Nil:
"y < x ⟹ [x .e. y ::'a::len word] = []"
by (simp add: upto_enum_red not_le word_less_nat_alt)
lemma word_enum_decomp_elem:
assumes "[x .e. (y ::'a::len word)] = as @ a # bs"
shows "x ≤ a ∧ a ≤ y"
proof -
have "set as ⊆ set [x .e. y] ∧ a ∈ set [x .e. y]"
using assms by (auto dest: arg_cong[where f=set])
then show ?thesis by auto
qed
lemma word_enum_prefix:
"[x .e. (y ::'a::len word)] = as @ a # bs ⟹ as = (if x < a then [x .e. a - 1] else [])"
apply (induct as arbitrary: x; clarsimp)
apply (case_tac "x < y")
prefer 2
apply (case_tac "x = y", simp)
apply (simp add: not_less)
apply (drule (1) dual_order.not_eq_order_implies_strict)
apply (simp add: word_upto_Nil)
apply (simp add: word_upto_Cons_eq)
apply (case_tac "x < y")
prefer 2
apply (case_tac "x = y", simp)
apply (simp add: not_less)
apply (drule (1) dual_order.not_eq_order_implies_strict)
apply (simp add: word_upto_Nil)
apply (clarsimp simp: word_upto_Cons_eq)
apply (frule word_enum_decomp_elem)
apply clarsimp
apply (rule conjI)
prefer 2
apply (subst word_Suc_le[symmetric]; clarsimp)
apply (drule meta_spec)
apply (drule (1) meta_mp)
apply clarsimp
apply (rule conjI; clarsimp)
apply (subst (2) word_upto_Cons_eq)
apply unat_arith
apply simp
done
lemma word_enum_decomp_set:
"[x .e. (y ::'a::len word)] = as @ a # bs ⟹ a ∉ set as"
by (metis distinct_append distinct_enum_upto' not_distinct_conv_prefix)
lemma word_enum_decomp:
assumes "[x .e. (y ::'a::len word)] = as @ a # bs"
shows "x ≤ a ∧ a ≤ y ∧ a ∉ set as ∧ (∀z ∈ set as. x ≤ z ∧ z ≤ y)"
proof -
from assms
have "set as ⊆ set [x .e. y] ∧ a ∈ set [x .e. y]"
by (auto dest: arg_cong[where f=set])
with word_enum_decomp_set[OF assms]
show ?thesis by auto
qed
lemma of_nat_unat_le_mask_ucast:
"⟦of_nat (unat t) = w; t ≤ mask LENGTH('a)⟧ ⟹ t = UCAST('a::len → 'b::len) w"
by (clarsimp simp: ucast_nat_def ucast_ucast_mask simp flip: and_mask_eq_iff_le_mask)
lemma less_diff_gt0:
"a < b ⟹ (0 :: 'a :: len word) < b - a"
by unat_arith
lemma unat_plus_gt:
"unat ((a :: 'a :: len word) + b) ≤ unat a + unat b"
by (clarsimp simp: unat_plus_if_size)
lemma const_less:
"⟦ (a :: 'a :: len word) - 1 < b; a ≠ b ⟧ ⟹ a < b"
by (metis less_1_simp word_le_less_eq)
lemma add_mult_aligned_neg_mask:
‹(x + y * m) AND NOT(mask n) = (x AND NOT(mask n)) + y * m›
if ‹m AND (2 ^ n - 1) = 0›
for x y m :: ‹'a::len word›
by (metis (no_types, opaque_lifting)
add.assoc add.commute add.right_neutral add_uminus_conv_diff
mask_eq_decr_exp mask_eqs(2) mask_eqs(6) mult.commute mult_zero_left
subtract_mask(1) that)
lemma unat_of_nat_minus_1:
"⟦ n < 2 ^ LENGTH('a); n ≠ 0 ⟧ ⟹ unat ((of_nat n:: 'a :: len word) - 1) = n - 1"
by (simp add: of_nat_diff unat_eq_of_nat)
lemma word_eq_zeroI:
"a ≤ a - 1 ⟹ a = 0" for a :: "'a :: len word"
by (simp add: word_must_wrap)
lemma word_add_format:
"(-1 :: 'a :: len word) + b + c = b + (c - 1)"
by simp
lemma upto_enum_word_nth:
"⟦ i ≤ j; k ≤ unat (j - i) ⟧ ⟹ [i .e. j] ! k = i + of_nat k"
apply (clarsimp simp: upto_enum_def nth_append)
apply (clarsimp simp: word_le_nat_alt[symmetric])
apply (rule conjI, clarsimp)
apply (subst toEnum_of_nat, unat_arith)
apply unat_arith
apply (clarsimp simp: not_less unat_sub[symmetric])
apply unat_arith
done
lemma upto_enum_step_nth:
"⟦ a ≤ c; n ≤ unat ((c - a) div (b - a)) ⟧
⟹ [a, b .e. c] ! n = a + of_nat n * (b - a)"
by (clarsimp simp: upto_enum_step_def not_less[symmetric] upto_enum_word_nth)
lemma upto_enum_inc_1_len:
"a < - 1 ⟹ [(0 :: 'a :: len word) .e. 1 + a] = [0 .e. a] @ [1 + a]"
apply (simp add: upto_enum_word)
apply (subgoal_tac "unat (1+a) = 1 + unat a")
apply simp
apply (subst unat_plus_simple[THEN iffD1])
apply (metis add.commute no_plus_overflow_neg olen_add_eqv)
apply unat_arith
done
lemma neg_mask_add:
"y AND mask n = 0 ⟹ x + y AND NOT(mask n) = (x AND NOT(mask n)) + y"
for x y :: ‹'a::len word›
by (clarsimp simp: mask_out_sub_mask mask_eqs(7)[symmetric] mask_twice)
lemma shiftr_shiftl_shiftr[simp]:
"(x :: 'a :: len word) >> a << a >> a = x >> a"
by (word_eqI_solve dest: bit_imp_le_length)
lemma add_right_shift:
"⟦ x AND mask n = 0; y AND mask n = 0; x ≤ x + y ⟧
⟹ (x + y :: ('a :: len) word) >> n = (x >> n) + (y >> n)"
apply (simp add: no_olen_add_nat is_aligned_mask[symmetric])
apply (simp add: unat_arith_simps shiftr_div_2n' split del: if_split)
apply (subst if_P)
apply (erule order_le_less_trans[rotated])
apply (simp add: add_mono)
apply (simp add: shiftr_div_2n' is_aligned_iff_dvd_nat)
done
lemma sub_right_shift:
"⟦ x AND mask n = 0; y AND mask n = 0; y ≤ x ⟧
⟹ (x - y) >> n = (x >> n :: 'a :: len word) - (y >> n)"
using add_right_shift[where x="x - y" and y=y and n=n]
by (simp add: aligned_sub_aligned is_aligned_mask[symmetric] word_sub_le)
lemma and_and_mask_simple:
"y AND mask n = mask n ⟹ (x AND y) AND mask n = x AND mask n"
by (simp add: ac_simps)
lemma and_and_mask_simple_not:
"y AND mask n = 0 ⟹ (x AND y) AND mask n = 0"
by (simp add: ac_simps)
lemma word_and_le':
"b ≤ c ⟹ (a :: 'a :: len word) AND b ≤ c"
by (metis word_and_le1 order_trans)
lemma word_and_less':
"b < c ⟹ (a :: 'a :: len word) AND b < c"
by transfer simp
lemma shiftr_w2p:
"x < LENGTH('a) ⟹ 2 ^ x = (2 ^ (LENGTH('a) - 1) >> (LENGTH('a) - 1 - x) :: 'a :: len word)"
by word_eqI_solve
lemma t2p_shiftr:
"⟦ b ≤ a; a < LENGTH('a) ⟧ ⟹ (2 :: 'a :: len word) ^ a >> b = 2 ^ (a - b)"
by word_eqI_solve
lemma scast_1[simp]:
"scast (1 :: 'a :: len signed word) = (1 :: 'a word)"
by simp
lemma unsigned_uminus1 [simp]:
‹(unsigned (-1::'b::len word)::'c::len word) = mask LENGTH('b)›
by (fact unsigned_minus_1_eq_mask)
lemma ucast_ucast_mask_eq:
"⟦ UCAST('a::len → 'b::len) x = y; x AND mask LENGTH('b) = x ⟧ ⟹ x = ucast y"
by (drule sym) (simp flip: take_bit_eq_mask add: unsigned_ucast_eq)
lemma ucast_up_eq:
"⟦ ucast x = (ucast y::'b::len word); LENGTH('a) ≤ LENGTH ('b) ⟧
⟹ ucast x = (ucast y::'a::len word)"
by (simp add: word_eq_iff bit_simps)
lemma ucast_up_neq:
"⟦ ucast x ≠ (ucast y::'b::len word); LENGTH('b) ≤ LENGTH ('a) ⟧
⟹ ucast x ≠ (ucast y::'a::len word)"
by (fastforce dest: ucast_up_eq)
lemma mask_AND_less_0:
"⟦ x AND mask n = 0; m ≤ n ⟧ ⟹ x AND mask m = 0"
for x :: ‹'a::len word›
by (metis mask_twice2 word_and_notzeroD)
lemma mask_len_id [simp]:
"(x :: 'a :: len word) AND mask LENGTH('a) = x"
using uint_lt2p [of x] by (simp add: mask_eq_iff)
lemma scast_ucast_down_same:
"LENGTH('b) ≤ LENGTH('a) ⟹ SCAST('a → 'b) = UCAST('a::len → 'b::len)"
by (simp add: down_cast_same is_down)
lemma word_aligned_0_sum:
"⟦ a + b = 0; is_aligned (a :: 'a :: len word) n; b ≤ mask n; n < LENGTH('a) ⟧
⟹ a = 0 ∧ b = 0"
by (simp add: word_plus_and_or_coroll aligned_mask_disjoint word_or_zero)
lemma mask_eq1_nochoice:
"⟦ LENGTH('a) > 1; (x :: 'a :: len word) AND 1 = x ⟧ ⟹ x = 0 ∨ x = 1"
by (metis word_and_1)
lemma shiftr_and_eq_shiftl:
"(w >> n) AND x = y ⟹ w AND (x << n) = (y << n)" for y :: "'a:: len word"
apply (drule sym)
apply simp
apply (rule bit_word_eqI)
apply (auto simp add: bit_simps)
done
lemma add_mask_lower_bits':
"⟦ len = LENGTH('a); is_aligned (x :: 'a :: len word) n;
∀n' ≥ n. n' < len ⟶ ¬ bit p n' ⟧
⟹ x + p AND NOT(mask n) = x"
using add_mask_lower_bits by auto
lemma leq_mask_shift:
"(x :: 'a :: len word) ≤ mask (low_bits + high_bits) ⟹ (x >> low_bits) ≤ mask high_bits"
by (simp add: le_mask_iff shiftr_shiftr ac_simps)
lemma ucast_ucast_eq_mask_shift:
"(x :: 'a :: len word) ≤ mask (low_bits + LENGTH('b))
⟹ ucast((ucast (x >> low_bits)) :: 'b :: len word) = x >> low_bits"
by (meson and_mask_eq_iff_le_mask eq_ucast_ucast_eq not_le_imp_less shiftr_less_t2n'
ucast_ucast_len)
lemma const_le_unat:
"⟦ b < 2 ^ LENGTH('a); of_nat b ≤ a ⟧ ⟹ b ≤ unat (a :: 'a :: len word)"
by (simp add: word_le_nat_alt unsigned_of_nat take_bit_nat_eq_self)
lemma upt_enum_offset_trivial:
"⟦ x < 2 ^ LENGTH('a) - 1 ; n ≤ unat x ⟧
⟹ ([(0 :: 'a :: len word) .e. x] ! n) = of_nat n"
apply (induct x arbitrary: n)
apply simp
by (simp add: upto_enum_word_nth)
lemma word_le_mask_out_plus_2sz:
"x ≤ (x AND NOT(mask sz)) + 2 ^ sz - 1"
for x :: ‹'a::len word›
by (metis add_diff_eq word_neg_and_le)
lemma ucast_add:
"ucast (a + (b :: 'a :: len word)) = ucast a + (ucast b :: ('a signed word))"
by transfer (simp add: take_bit_add)
lemma ucast_minus:
"ucast (a - (b :: 'a :: len word)) = ucast a - (ucast b :: ('a signed word))"
apply (insert ucast_add[where a=a and b="-b"])
apply (metis (no_types, opaque_lifting) add_diff_eq diff_add_cancel ucast_add)
done
lemma scast_ucast_add_one [simp]:
"scast (ucast (x :: 'a::len word) + (1 :: 'a signed word)) = x + 1"
apply (subst ucast_1[symmetric])
apply (subst ucast_add[symmetric])
apply clarsimp
done
lemma word_and_le_plus_one:
"a > 0 ⟹ (x :: 'a :: len word) AND (a - 1) < a"
by (simp add: gt0_iff_gem1 word_and_less')
lemma unat_of_ucast_then_shift_eq_unat_of_shift[simp]:
"LENGTH('b) ≥ LENGTH('a)
⟹ unat ((ucast (x :: 'a :: len word) :: 'b :: len word) >> n) = unat (x >> n)"
by (simp add: shiftr_div_2n' unat_ucast_up_simp)
lemma unat_of_ucast_then_mask_eq_unat_of_mask[simp]:
"LENGTH('b) ≥ LENGTH('a)
⟹ unat ((ucast (x :: 'a :: len word) :: 'b :: len word) AND mask m) = unat (x AND mask m)"
by (metis ucast_and_mask unat_ucast_up_simp)
lemma shiftr_less_t2n3:
"⟦ (2 :: 'a word) ^ (n + m) = 0; m < LENGTH('a) ⟧
⟹ (x :: 'a :: len word) >> n < 2 ^ m"
by (fastforce intro: shiftr_less_t2n' simp: mask_eq_decr_exp power_overflow)
lemma unat_shiftr_le_bound:
"⟦ 2 ^ (LENGTH('a :: len) - n) - 1 ≤ bnd; 0 < n ⟧
⟹ unat ((x :: 'a word) >> n) ≤ bnd"
apply transfer
apply (simp add: take_bit_drop_bit)
apply (simp add: drop_bit_take_bit)
apply (rule order_trans)
defer
apply assumption
apply (simp add: nat_le_iff of_nat_diff)
done
lemma shiftr_eqD:
"⟦ x >> n = y >> n; is_aligned x n; is_aligned y n ⟧
⟹ x = y"
by (metis is_aligned_shiftr_shiftl)
lemma word_shiftr_shiftl_shiftr_eq_shiftr:
"a ≥ b ⟹ (x :: 'a :: len word) >> a << b >> b = x >> a"
apply (rule bit_word_eqI)
apply (auto simp add: bit_simps dest: bit_imp_le_length)
done
lemma of_int_uint_ucast:
"of_int (uint (x :: 'a::len word)) = (ucast x :: 'b::len word)"
by (fact Word.of_int_uint)
lemma mod_mask_drop:
"⟦ m = 2 ^ n; 0 < m; mask n AND msk = mask n ⟧
⟹ (x mod m) AND msk = x mod m"
for x :: ‹'a::len word›
by (simp add: word_mod_2p_is_mask word_bw_assocs)
lemma mask_eq_ucast_eq:
"⟦ x AND mask LENGTH('a) = (x :: ('c :: len word));
LENGTH('a) ≤ LENGTH('b)⟧
⟹ ucast (ucast x :: ('a :: len word)) = (ucast x :: ('b :: len word))"
by (metis ucast_and_mask ucast_id ucast_ucast_mask ucast_up_eq)
lemma of_nat_less_t2n:
"of_nat i < (2 :: ('a :: len) word) ^ n ⟹ n < LENGTH('a) ∧ unat (of_nat i :: 'a word) < 2 ^ n"
by (metis order_less_trans p2_gt_0 unat_less_power word_neq_0_conv)
lemma two_power_increasing_less_1:
"⟦ n ≤ m; m ≤ LENGTH('a) ⟧ ⟹ (2 :: 'a :: len word) ^ n - 1 ≤ 2 ^ m - 1"
by (metis diff_diff_cancel le_m1_iff_lt less_imp_diff_less p2_gt_0 two_power_increasing
word_1_le_power word_le_minus_mono_left word_less_sub_1)
lemma word_sub_mono4:
"⟦ y + x ≤ z + x; y ≤ y + x; z ≤ z + x ⟧ ⟹ y ≤ z" for y :: "'a :: len word"
by (simp add: word_add_le_iff2)
lemma eq_or_less_helperD:
"⟦ n = unat (2 ^ m - 1 :: 'a :: len word) ∨ n < unat (2 ^ m - 1 :: 'a word); m < LENGTH('a) ⟧
⟹ n < 2 ^ m"
by (meson le_less_trans nat_less_le unat_less_power word_power_less_1)
lemma mask_sub:
"n ≤ m ⟹ mask m - mask n = mask m AND NOT(mask n :: 'a::len word)"
by (metis (full_types) and_mask_eq_iff_shiftr_0 mask_out_sub_mask shiftr_mask_le word_bw_comms(1))
lemma neg_mask_diff_bound:
"sz'≤ sz ⟹ (ptr AND NOT(mask sz')) - (ptr AND NOT(mask sz)) ≤ 2 ^ sz - 2 ^ sz'"
(is "_ ⟹ ?lhs ≤ ?rhs")
for ptr :: ‹'a::len word›
proof -
assume lt: "sz' ≤ sz"
hence "?lhs = ptr AND (mask sz AND NOT(mask sz'))"
by (metis add_diff_cancel_left' multiple_mask_trivia)
also have "… ≤ ?rhs" using lt
by (metis (mono_tags) add_diff_eq diff_eq_eq eq_iff mask_2pm1 mask_sub word_and_le')
finally show ?thesis by simp
qed
lemma mask_out_eq_0:
"⟦ idx < 2 ^ sz; sz < LENGTH('a) ⟧ ⟹ (of_nat idx :: 'a :: len word) AND NOT(mask sz) = 0"
by (simp add: of_nat_power less_mask_eq mask_eq_0_eq_x)
lemma is_aligned_neg_mask_eq':
"is_aligned ptr sz = (ptr AND NOT(mask sz) = ptr)"
using is_aligned_mask mask_eq_0_eq_x by blast
lemma neg_mask_mask_unat:
"sz < LENGTH('a)
⟹ unat ((ptr :: 'a :: len word) AND NOT(mask sz)) + unat (ptr AND mask sz) = unat ptr"
by (metis AND_NOT_mask_plus_AND_mask_eq unat_plus_simple word_and_le2)
lemma unat_pow_le_intro:
"LENGTH('a) ≤ n ⟹ unat (x :: 'a :: len word) < 2 ^ n"
by (metis lt2p_lem not_le of_nat_le_iff of_nat_numeral semiring_1_class.of_nat_power uint_nat)
lemma unat_shiftl_less_t2n:
‹unat (x << n) < 2 ^ m›
if ‹unat (x :: 'a :: len word) < 2 ^ (m - n)› ‹m < LENGTH('a)›
proof (cases ‹n ≤ m›)
case False
with that show ?thesis
apply (transfer fixing: m n)
apply (simp add: not_le take_bit_push_bit)
apply (metis diff_le_self order_le_less_trans push_bit_of_0 take_bit_0 take_bit_int_eq_self
take_bit_int_less_exp take_bit_nonnegative take_bit_tightened)
done
next
case True
moreover define q r where ‹q = m - n› and ‹r = LENGTH('a) - n - q›
ultimately have ‹m - n = q› ‹m = n + q› ‹LENGTH('a) = r + q + n›
using that by simp_all
with that show ?thesis
apply (transfer fixing: m n q r)
apply (simp add: not_le take_bit_push_bit)
apply (simp add: push_bit_eq_mult power_add)
using take_bit_tightened_less_eq_int [of ‹r + q› ‹r + q + n›]
apply (rule le_less_trans)
apply simp_all
done
qed
lemma unat_is_aligned_add:
"⟦ is_aligned p n; unat d < 2 ^ n ⟧
⟹ unat (p + d AND mask n) = unat d ∧ unat (p + d AND NOT(mask n)) = unat p"
by (metis add.right_neutral and_mask_eq_iff_le_mask and_not_mask le_mask_iff mask_add_aligned
mask_out_add_aligned mult_zero_right shiftl_t2n shiftr_le_0)
lemma unat_shiftr_shiftl_mask_zero:
"⟦ c + a ≥ LENGTH('a) + b ; c < LENGTH('a) ⟧
⟹ unat (((q :: 'a :: len word) >> a << b) AND NOT(mask c)) = 0"
by (fastforce intro: unat_is_aligned_add[where p=0 and n=c, simplified, THEN conjunct2]
unat_shiftl_less_t2n unat_shiftr_less_t2n unat_pow_le_intro)
lemmas of_nat_ucast = ucast_of_nat[symmetric]
lemma shift_then_mask_eq_shift_low_bits:
"x ≤ mask (low_bits + high_bits) ⟹ (x >> low_bits) AND mask high_bits = x >> low_bits"
for x :: ‹'a::len word›
by (simp add: leq_mask_shift le_mask_imp_and_mask)
lemma leq_low_bits_iff_zero:
"⟦ x ≤ mask (low bits + high bits); x >> low_bits = 0 ⟧ ⟹ (x AND mask low_bits = 0) = (x = 0)"
for x :: ‹'a::len word›
using and_mask_eq_iff_shiftr_0 by force
lemma unat_less_iff:
"⟦ unat (a :: 'a :: len word) = b; c < 2 ^ LENGTH('a) ⟧ ⟹ (a < of_nat c) = (b < c)"
using unat_ucast_less_no_overflow_simp by blast
lemma is_aligned_no_overflow3:
"⟦ is_aligned (a :: 'a :: len word) n; n < LENGTH('a); b < 2 ^ n; c ≤ 2 ^ n; b < c ⟧
⟹ a + b ≤ a + (c - 1)"
by (meson is_aligned_no_wrap' le_m1_iff_lt not_le word_less_sub_1 word_plus_mono_right)
lemma mask_add_aligned_right:
"is_aligned p n ⟹ (q + p) AND mask n = q AND mask n"
by (simp add: mask_add_aligned add.commute)
lemma leq_high_bits_shiftr_low_bits_leq_bits_mask:
"x ≤ mask high_bits ⟹ (x :: 'a :: len word) << low_bits ≤ mask (low_bits + high_bits)"
by (metis le_mask_shiftl_le_mask)
lemma word_two_power_neg_ineq:
"2 ^ m ≠ (0 :: 'a word) ⟹ 2 ^ n ≤ - (2 ^ m :: 'a :: len word)"
apply (cases "n < LENGTH('a)"; simp add: power_overflow)
apply (cases "m < LENGTH('a)"; simp add: power_overflow)
apply (simp add: word_le_nat_alt unat_minus word_size)
apply (cases "LENGTH('a)"; simp)
apply (simp add: less_Suc_eq_le)
apply (drule power_increasing[where a=2 and n=n] power_increasing[where a=2 and n=m], simp)+
apply (drule(1) add_le_mono)
apply simp
done
lemma unat_shiftl_absorb:
"⟦ x ≤ 2 ^ p; p + k < LENGTH('a) ⟧ ⟹ unat (x :: 'a :: len word) * 2 ^ k = unat (x * 2 ^ k)"
by (smt (verit) add_diff_cancel_right' add_lessD1 le_add2 le_less_trans mult.commute nat_le_power_trans
unat_lt2p unat_mult_lem unat_power_lower word_le_nat_alt)
lemma word_plus_mono_right_split:
"⟦ unat ((x :: 'a :: len word) AND mask sz) + unat z < 2 ^ sz; sz < LENGTH('a) ⟧
⟹ x ≤ x + z"
apply (subgoal_tac "(x AND NOT(mask sz)) + (x AND mask sz) ≤ (x AND NOT(mask sz)) + ((x AND mask sz) + z)")
apply (simp add:word_plus_and_or_coroll2 field_simps)
apply (rule word_plus_mono_right)
apply (simp add: less_le_trans no_olen_add_nat)
using of_nat_power is_aligned_no_wrap' by force
lemma mul_not_mask_eq_neg_shiftl:
"NOT(mask n :: 'a::len word) = -1 << n"
by (simp add: NOT_mask shiftl_t2n)
lemma shiftr_mul_not_mask_eq_and_not_mask:
"(x >> n) * NOT(mask n) = - (x AND NOT(mask n))"
for x :: ‹'a::len word›
by (metis NOT_mask and_not_mask mult_minus_left semiring_normalization_rules(7) shiftl_t2n)
lemma mask_eq_n1_shiftr:
"n ≤ LENGTH('a) ⟹ (mask n :: 'a :: len word) = -1 >> (LENGTH('a) - n)"
by (metis diff_diff_cancel eq_refl mask_full shiftr_mask2)
lemma is_aligned_mask_out_add_eq:
"is_aligned p n ⟹ (p + x) AND NOT(mask n) = p + (x AND NOT(mask n))"
by (simp add: mask_out_sub_mask mask_add_aligned)
lemmas is_aligned_mask_out_add_eq_sub
= is_aligned_mask_out_add_eq[where x="a - b" for a b, simplified field_simps]
lemma aligned_bump_down:
"is_aligned x n ⟹ (x - 1) AND NOT(mask n) = x - 2 ^ n"
by (drule is_aligned_mask_out_add_eq[where x="-1"]) (simp add: NOT_mask)
lemma unat_2tp_if:
"unat (2 ^ n :: ('a :: len) word) = (if n < LENGTH ('a) then 2 ^ n else 0)"
by (split if_split, simp_all add: power_overflow)
lemma mask_of_mask:
"mask (n::nat) AND mask (m::nat) = (mask (min m n) :: 'a::len word)"
by word_eqI_solve
lemma unat_signed_ucast_less_ucast:
"LENGTH('a) ≤ LENGTH('b) ⟹ unat (ucast (x :: 'a :: len word) :: 'b :: len signed word) = unat x"
by (simp add: unat_ucast_up_simp)
lemma toEnum_of_ucast:
"LENGTH('b) ≤ LENGTH('a) ⟹
(toEnum (unat (b::'b :: len word))::'a :: len word) = of_nat (unat b)"
by (simp add: unat_pow_le_intro)
lemma plus_mask_AND_NOT_mask_eq:
"x AND NOT(mask n) = x ⟹ (x + mask n) AND NOT(mask n) = x" for x::‹'a::len word›
apply (subst word_plus_and_or_coroll; word_eqI; fastforce?)
apply (erule allE, drule (1) iffD2)
apply clarsimp
done
lemmas unat_ucast_mask = unat_ucast_eq_unat_and_mask[where w=a for a]
lemma t2n_mask_eq_if:
"2 ^ n AND mask m = (if n < m then 2 ^ n else (0 :: 'a::len word))"
by word_eqI_solve
lemma unat_ucast_le:
"unat (ucast (x :: 'a :: len word) :: 'b :: len word) ≤ unat x"
by (simp add: ucast_nat_def word_unat_less_le)
lemma ucast_le_up_down_iff:
"⟦ LENGTH('a) ≤ LENGTH('b); (x :: 'b :: len word) ≤ ucast (- 1 :: 'a :: len word) ⟧
⟹ (ucast x ≤ (y :: 'a word)) = (x ≤ ucast y)"
using le_max_word_ucast_id ucast_le_ucast by metis
lemma ucast_ucast_mask_shift:
"a ≤ LENGTH('a) + b
⟹ ucast (ucast (p AND mask a >> b) :: 'a :: len word) = p AND mask a >> b"
by (metis add.commute le_mask_iff shiftr_mask_le ucast_ucast_eq_mask_shift word_and_le')
lemma unat_ucast_mask_shift:
"a ≤ LENGTH('a) + b
⟹ unat (ucast (p AND mask a >> b) :: 'a :: len word) = unat (p AND mask a >> b)"
by (metis linear ucast_ucast_mask_shift unat_ucast_up_simp)
lemma mask_overlap_zero:
"a ≤ b ⟹ (p AND mask a) AND NOT(mask b) = 0"
for p :: ‹'a::len word›
by (metis NOT_mask_AND_mask mask_lower_twice2 max_def)
lemma mask_shifl_overlap_zero:
"a + c ≤ b ⟹ (p AND mask a << c) AND NOT(mask b) = 0"
for p :: ‹'a::len word›
by (metis and_mask_0_iff_le_mask mask_mono mask_shiftl_decompose order_trans shiftl_over_and_dist word_and_le' word_and_le2)
lemma mask_overlap_zero':
"a ≥ b ⟹ (p AND NOT(mask a)) AND mask b = 0"
for p :: ‹'a::len word›
using mask_AND_NOT_mask mask_AND_less_0 by blast
lemma mask_rshift_mult_eq_rshift_lshift:
"((a :: 'a :: len word) >> b) * (1 << c) = (a >> b << c)"
by (simp add: shiftl_t2n)
lemma shift_alignment:
"a ≥ b ⟹ is_aligned (p >> a << a) b"
using is_aligned_shift is_aligned_weaken by blast
lemma mask_split_sum_twice:
"a ≥ b ⟹ (p AND NOT(mask a)) + ((p AND mask a) AND NOT(mask b)) + (p AND mask b) = p"
for p :: ‹'a::len word›
by (simp add: add.commute multiple_mask_trivia word_bw_comms(1) word_bw_lcs(1) word_plus_and_or_coroll2)
lemma mask_shift_eq_mask_mask:
"(p AND mask a >> b << b) = (p AND mask a) AND NOT(mask b)"
for p :: ‹'a::len word›
by (simp add: and_not_mask)
lemma mask_shift_sum:
"⟦ a ≥ b; unat n = unat (p AND mask b) ⟧
⟹ (p AND NOT(mask a)) + (p AND mask a >> b) * (1 << b) + n = (p :: 'a :: len word)"
apply (simp add: shiftl_def shiftr_def flip: push_bit_eq_mult take_bit_eq_mask word_unat_eq_iff)
apply (subst disjunctive_add)
apply (auto simp add: bit_simps)
apply (subst disjunctive_add)
apply (auto simp add: bit_simps)
apply (rule bit_word_eqI)
apply (auto simp add: bit_simps)
done
lemma is_up_compose:
"⟦ is_up uc; is_up uc' ⟧ ⟹ is_up (uc' ∘ uc)"
unfolding is_up_def by (simp add: Word.target_size Word.source_size)
lemma of_int_sint_scast:
"of_int (sint (x :: 'a :: len word)) = (scast x :: 'b :: len word)"
by (fact Word.of_int_sint)
lemma scast_of_nat_to_signed [simp]:
"scast (of_nat x :: 'a :: len word) = (of_nat x :: 'a signed word)"
by (rule bit_word_eqI) (simp add: bit_simps)
lemma scast_of_nat_signed_to_unsigned_add:
"scast (of_nat x + of_nat y :: 'a :: len signed word) = (of_nat x + of_nat y :: 'a :: len word)"
by (metis of_nat_add scast_of_nat)
lemma scast_of_nat_unsigned_to_signed_add:
"(scast (of_nat x + of_nat y :: 'a :: len word)) = (of_nat x + of_nat y :: 'a :: len signed word)"
by (metis Abs_fnat_hom_add scast_of_nat_to_signed)
lemma and_mask_cases:
fixes x :: "'a :: len word"
assumes len: "n < LENGTH('a)"
shows "x AND mask n ∈ of_nat ` set [0 ..< 2 ^ n]"
apply (simp flip: take_bit_eq_mask)
apply (rule image_eqI [of _ _ ‹unat (take_bit n x)›])
using len apply simp_all
apply transfer
apply simp
done
lemma sint_eq_uint_2pl:
"⟦ (a :: 'a :: len word) < 2 ^ (LENGTH('a) - 1) ⟧
⟹ sint a = uint a"
by (simp add: not_msb_from_less sint_eq_uint word_2p_lem word_size)
lemma pow_sub_less:
"⟦ a + b ≤ LENGTH('a); unat (x :: 'a :: len word) = 2 ^ a ⟧
⟹ unat (x * 2 ^ b - 1) < 2 ^ (a + b)"
by (smt (verit) eq_or_less_helperD le_add2 le_eq_less_or_eq le_trans power_add unat_mult_lem unat_pow_le_intro unat_power_lower word_eq_unatI)
lemma sle_le_2pl:
"⟦ (b :: 'a :: len word) < 2 ^ (LENGTH('a) - 1); a ≤ b ⟧ ⟹ a <=s b"
by (simp add: not_msb_from_less word_sle_msb_le)
lemma sless_less_2pl:
"⟦ (b :: 'a :: len word) < 2 ^ (LENGTH('a) - 1); a < b ⟧ ⟹ a <s b"
using not_msb_from_less word_sless_msb_less by blast
lemma and_mask2:
"w << n >> n = w AND mask (size w - n)"
for w :: ‹'a::len word›
by (rule bit_word_eqI) (auto simp add: bit_simps word_size)
lemma aligned_sub_aligned_simple:
"⟦ is_aligned a n; is_aligned b n ⟧ ⟹ is_aligned (a - b) n"
by (simp add: aligned_sub_aligned)
lemma minus_one_shift:
"- (1 << n) = (-1 << n :: 'a::len word)"
by (simp add: shiftl_def minus_exp_eq_not_mask)
lemma ucast_eq_mask:
"(UCAST('a::len → 'b::len) x = UCAST('a → 'b) y) =
(x AND mask LENGTH('b) = y AND mask LENGTH('b))"
by transfer (simp flip: take_bit_eq_mask add: ac_simps)
context
fixes w :: "'a::len word"
begin
private lemma sbintrunc_uint_ucast:
‹signed_take_bit n (uint (ucast w :: 'b word)) = signed_take_bit n (uint w)› if ‹Suc n = LENGTH('b::len)›
by (rule bit_eqI) (use that in ‹auto simp add: bit_simps›)
private lemma test_bit_sbintrunc:
assumes "i < LENGTH('a)"
shows "bit (word_of_int (signed_take_bit n (uint w)) :: 'a word) i
= (if n < i then bit w n else bit w i)"
using assms by (simp add: bit_simps)
private lemma test_bit_sbintrunc_ucast:
assumes len_a: "i < LENGTH('a)"
shows "bit (word_of_int (signed_take_bit (LENGTH('b) - 1) (uint (ucast w :: 'b word))) :: 'a word) i
= (if LENGTH('b::len) ≤ i then bit w (LENGTH('b) - 1) else bit w i)"
using len_a by (auto simp add: sbintrunc_uint_ucast bit_simps)
lemma scast_ucast_high_bits:
‹scast (ucast w :: 'b::len word) = w
⟷ (∀ i ∈ {LENGTH('b) ..< size w}. bit w i = bit w (LENGTH('b) - 1))›
proof (cases ‹LENGTH('a) ≤ LENGTH('b)›)
case True
moreover define m where ‹m = LENGTH('b) - LENGTH('a)›
ultimately have ‹LENGTH('b) = m + LENGTH('a)›
by simp
then show ?thesis
by (simp add: signed_ucast_eq word_size) word_eqI
next
case False
define q where ‹q = LENGTH('b) - 1›
then have ‹LENGTH('b) = Suc q›
by simp
moreover define m where ‹m = Suc LENGTH('a) - LENGTH('b)›
with False ‹LENGTH('b) = Suc q› have ‹LENGTH('a) = m + q›
by (simp add: not_le)
ultimately show ?thesis
apply (simp add: signed_ucast_eq word_size)
apply (transfer fixing: m q)
apply (simp add: signed_take_bit_take_bit)
apply (rule impI)
apply (subst bit_eq_iff)
apply (simp add: bit_take_bit_iff bit_signed_take_bit_iff min_def)
apply (auto simp add: Suc_le_eq)
using less_imp_le_nat apply blast
using less_imp_le_nat apply blast
done
qed
lemma scast_ucast_mask_compare:
"scast (ucast w :: 'b::len word) = w
⟷ (w ≤ mask (LENGTH('b) - 1) ∨ NOT(mask (LENGTH('b) - 1)) ≤ w)"
apply (clarsimp simp: le_mask_high_bits neg_mask_le_high_bits scast_ucast_high_bits word_size)
apply (rule iffI; clarsimp)
apply (rename_tac i j; case_tac "i = LENGTH('b) - 1"; case_tac "j = LENGTH('b) - 1")
by auto
lemma ucast_less_shiftl_helper':
"⟦ LENGTH('b) + (a::nat) < LENGTH('a); 2 ^ (LENGTH('b) + a) ≤ n⟧
⟹ (ucast (x :: 'b::len word) << a) < (n :: 'a::len word)"
apply (erule order_less_le_trans[rotated])
using ucast_less[where x=x and 'a='a]
apply (simp only: shiftl_t2n field_simps)
apply (rule word_less_power_trans2; simp)
done
end
lemma ucast_ucast_mask2:
"is_down (UCAST ('a → 'b)) ⟹
UCAST ('b::len → 'c::len) (UCAST ('a::len → 'b::len) x) = UCAST ('a → 'c) (x AND mask LENGTH('b))"
by word_eqI_solve
lemma ucast_NOT:
"ucast (NOT x) = NOT(ucast x) AND mask (LENGTH('a))" for x::"'a::len word"
by word_eqI_solve
lemma ucast_NOT_down:
"is_down UCAST('a::len → 'b::len) ⟹ UCAST('a → 'b) (NOT x) = NOT(UCAST('a → 'b) x)"
by word_eqI
lemma upto_enum_step_shift:
"is_aligned p n ⟹ ([p , p + 2 ^ m .e. p + 2 ^ n - 1]) = map ((+) p) [0, 2 ^ m .e. 2 ^ n - 1]"
apply (erule is_aligned_get_word_bits)
prefer 2
apply (simp add: map_idI)
apply (clarsimp simp: upto_enum_step_def)
apply (frule is_aligned_no_overflow)
apply (simp add: linorder_not_le [symmetric])
done
lemma upto_enum_step_shift_red:
"⟦ is_aligned p sz; sz < LENGTH('a); us ≤ sz ⟧
⟹ [p :: 'a :: len word, p + 2 ^ us .e. p + 2 ^ sz - 1]
= map (λx. p + of_nat x * 2 ^ us) [0 ..< 2 ^ (sz - us)]"
apply (subst upto_enum_step_shift, assumption)
apply (simp add: upto_enum_step_red)
done
lemma upto_enum_step_subset:
"set [x, y .e. z] ⊆ {x .. z}"
apply (clarsimp simp: upto_enum_step_def linorder_not_less)
apply (drule div_to_mult_word_lt)
apply (rule conjI)
apply (erule word_random[rotated])
apply simp
apply (rule order_trans)
apply (erule word_plus_mono_right)
apply simp
apply simp
done
lemma ucast_distrib:
fixes M :: "'a::len word ⇒ 'a::len word ⇒ 'a::len word"
fixes M' :: "'b::len word ⇒ 'b::len word ⇒ 'b::len word"
fixes L :: "int ⇒ int ⇒ int"
assumes lift_M: "⋀x y. uint (M x y) = L (uint x) (uint y) mod 2 ^ LENGTH('a)"
assumes lift_M': "⋀x y. uint (M' x y) = L (uint x) (uint y) mod 2 ^ LENGTH('b)"
assumes distrib: "⋀x y. (L (x mod (2 ^ LENGTH('b))) (y mod (2 ^ LENGTH('b)))) mod (2 ^ LENGTH('b))
= (L x y) mod (2 ^ LENGTH('b))"
assumes is_down: "is_down (ucast :: 'a word ⇒ 'b word)"
shows "ucast (M a b) = M' (ucast a) (ucast b)"
apply (simp only: ucast_eq)
apply (subst lift_M)
apply (subst of_int_uint [symmetric], subst lift_M')
apply (metis local.distrib local.is_down take_bit_eq_mod ucast_down_wi uint_word_of_int_eq word_of_int_uint)
done
lemma ucast_down_add:
"is_down (ucast:: 'a word ⇒ 'b word) ⟹ ucast ((a :: 'a::len word) + b) = (ucast a + ucast b :: 'b::len word)"
by (rule ucast_distrib [where L="(+)"], (clarsimp simp: uint_word_ariths)+, presburger, simp)
lemma ucast_down_minus:
"is_down (ucast:: 'a word ⇒ 'b word) ⟹ ucast ((a :: 'a::len word) - b) = (ucast a - ucast b :: 'b::len word)"
apply (rule ucast_distrib [where L="(-)"], (clarsimp simp: uint_word_ariths)+)
apply (metis mod_diff_left_eq mod_diff_right_eq)
apply simp
done
lemma ucast_down_mult:
"is_down (ucast:: 'a word ⇒ 'b word) ⟹ ucast ((a :: 'a::len word) * b) = (ucast a * ucast b :: 'b::len word)"
apply (rule ucast_distrib [where L="(*)"], (clarsimp simp: uint_word_ariths)+)
apply (metis mod_mult_eq)
apply simp
done
lemma scast_distrib:
fixes M :: "'a::len word ⇒ 'a::len word ⇒ 'a::len word"
fixes M' :: "'b::len word ⇒ 'b::len word ⇒ 'b::len word"
fixes L :: "int ⇒ int ⇒ int"
assumes lift_M: "⋀x y. uint (M x y) = L (uint x) (uint y) mod 2 ^ LENGTH('a)"
assumes lift_M': "⋀x y. uint (M' x y) = L (uint x) (uint y) mod 2 ^ LENGTH('b)"
assumes distrib: "⋀x y. (L (x mod (2 ^ LENGTH('b))) (y mod (2 ^ LENGTH('b)))) mod (2 ^ LENGTH('b))
= (L x y) mod (2 ^ LENGTH('b))"
assumes is_down: "is_down (scast :: 'a word ⇒ 'b word)"
shows "scast (M a b) = M' (scast a) (scast b)"
apply (subst (1 2 3) down_cast_same [symmetric])
apply (insert is_down)
apply (clarsimp simp: is_down_def target_size source_size is_down)
apply (rule ucast_distrib [where L=L, OF lift_M lift_M' distrib])
apply (insert is_down)
apply (clarsimp simp: is_down_def target_size source_size is_down)
done
lemma scast_down_add:
"is_down (scast:: 'a word ⇒ 'b word) ⟹ scast ((a :: 'a::len word) + b) = (scast a + scast b :: 'b::len word)"
by (rule scast_distrib [where L="(+)"], (clarsimp simp: uint_word_ariths)+, presburger, simp)
lemma scast_down_minus:
"is_down (scast:: 'a word ⇒ 'b word) ⟹ scast ((a :: 'a::len word) - b) = (scast a - scast b :: 'b::len word)"
apply (rule scast_distrib [where L="(-)"], (clarsimp simp: uint_word_ariths)+)
apply (metis mod_diff_left_eq mod_diff_right_eq)
apply simp
done
lemma scast_down_mult:
"is_down (scast:: 'a word ⇒ 'b word) ⟹ scast ((a :: 'a::len word) * b) = (scast a * scast b :: 'b::len word)"
apply (rule scast_distrib [where L="(*)"], (clarsimp simp: uint_word_ariths)+)
apply (metis mod_mult_eq)
apply simp
done
lemma scast_ucast_1:
"⟦ is_down (ucast :: 'a word ⇒ 'b word); is_down (ucast :: 'b word ⇒ 'c word) ⟧ ⟹
(scast (ucast (a :: 'a::len word) :: 'b::len word) :: 'c::len word) = ucast a"
by (metis down_cast_same ucast_eq ucast_down_wi)
lemma scast_ucast_3:
"⟦ is_down (ucast :: 'a word ⇒ 'c word); is_down (ucast :: 'b word ⇒ 'c word) ⟧ ⟹
(scast (ucast (a :: 'a::len word) :: 'b::len word) :: 'c::len word) = ucast a"
by (metis down_cast_same ucast_eq ucast_down_wi)
lemma scast_ucast_4:
"⟦ is_up (ucast :: 'a word ⇒ 'b word); is_down (ucast :: 'b word ⇒ 'c word) ⟧ ⟹
(scast (ucast (a :: 'a::len word) :: 'b::len word) :: 'c::len word) = ucast a"
by (metis down_cast_same ucast_eq ucast_down_wi)
lemma scast_scast_b:
"⟦ is_up (scast :: 'a word ⇒ 'b word) ⟧ ⟹
(scast (scast (a :: 'a::len word) :: 'b::len word) :: 'c::len word) = scast a"
by (metis scast_eq sint_up_scast)
lemma ucast_scast_1:
"⟦ is_down (scast :: 'a word ⇒ 'b word); is_down (ucast :: 'b word ⇒ 'c word) ⟧ ⟹
(ucast (scast (a :: 'a::len word) :: 'b::len word) :: 'c::len word) = scast a"
by (metis scast_eq ucast_down_wi)
lemma ucast_scast_3:
"⟦ is_down (scast :: 'a word ⇒ 'c word); is_down (ucast :: 'b word ⇒ 'c word) ⟧ ⟹
(ucast (scast (a :: 'a::len word) :: 'b::len word) :: 'c::len word) = scast a"
by (metis scast_eq ucast_down_wi)
lemma ucast_scast_4:
"⟦ is_up (scast :: 'a word ⇒ 'b word); is_down (ucast :: 'b word ⇒ 'c word) ⟧ ⟹
(ucast (scast (a :: 'a::len word) :: 'b::len word) :: 'c::len word) = scast a"
by (metis down_cast_same scast_eq sint_up_scast)
lemma ucast_ucast_a:
"⟦ is_down (ucast :: 'b word ⇒ 'c word) ⟧ ⟹
(ucast (ucast (a :: 'a::len word) :: 'b::len word) :: 'c::len word) = ucast a"
by (metis down_cast_same ucast_eq ucast_down_wi)
lemma ucast_ucast_b:
"⟦ is_up (ucast :: 'a word ⇒ 'b word) ⟧ ⟹
(ucast (ucast (a :: 'a::len word) :: 'b::len word) :: 'c::len word) = ucast a"
by (metis ucast_up_ucast)
lemma scast_scast_a:
"⟦ is_down (scast :: 'b word ⇒ 'c word) ⟧ ⟹
(scast (scast (a :: 'a::len word) :: 'b::len word) :: 'c::len word) = scast a"
apply (simp only: scast_eq)
apply (metis down_cast_same is_up_down scast_eq ucast_down_wi)
done
lemma scast_down_wi [OF refl]:
"uc = scast ⟹ is_down uc ⟹ uc (word_of_int x) = word_of_int x"
by (metis down_cast_same is_up_down ucast_down_wi)
lemmas cast_simps =
is_down is_up
scast_down_add scast_down_minus scast_down_mult
ucast_down_add ucast_down_minus ucast_down_mult
scast_ucast_1 scast_ucast_3 scast_ucast_4
ucast_scast_1 ucast_scast_3 ucast_scast_4
ucast_ucast_a ucast_ucast_b
scast_scast_a scast_scast_b
ucast_down_wi scast_down_wi
ucast_of_nat scast_of_nat
uint_up_ucast sint_up_scast
up_scast_surj up_ucast_surj
lemma sdiv_word_max:
"(sint (a :: ('a::len) word) sdiv sint (b :: ('a::len) word) < (2 ^ (size a - 1))) =
((a ≠ - (2 ^ (size a - 1)) ∨ (b ≠ -1)))"
(is "?lhs = (¬ ?a_int_min ∨ ¬ ?b_minus1)")
proof (rule classical)
assume not_thesis: "¬ ?thesis"
have not_zero: "b ≠ 0"
using not_thesis
by (clarsimp)
let ?range = ‹{- (2 ^ (size a - 1))..<2 ^ (size a - 1)} :: int set›
have result_range: "sint a sdiv sint b ∈ ?range ∪ {2 ^ (size a - 1)}"
using sdiv_word_min [of a b] sdiv_word_max [of a b] by auto
have result_range_overflow: "(sint a sdiv sint b = 2 ^ (size a - 1)) = (?a_int_min ∧ ?b_minus1)"
apply (rule iffI [rotated])
apply (clarsimp simp: signed_divide_int_def sgn_if word_size sint_int_min)
apply (rule classical)
apply (case_tac "?a_int_min")
apply (clarsimp simp: word_size sint_int_min)
apply (metis diff_0_right
int_sdiv_negated_is_minus1 minus_diff_eq minus_int_code(2)
power_eq_0_iff sint_minus1 zero_neq_numeral)
apply (subgoal_tac "abs (sint a) < 2 ^ (size a - 1)")
apply (insert sdiv_int_range [where a="sint a" and b="sint b"])[1]
apply (clarsimp simp: word_size)
apply (insert sdiv_int_range [where a="sint a" and b="sint b"])[1]
apply auto
apply (cases ‹size a›)
apply simp_all
apply (smt (verit) One_nat_def diff_Suc_1 signed_word_eqI sint_int_min sint_range_size wsst_TYs(3))
done
have result_range_simple: "(sint a sdiv sint b ∈ ?range) ⟹ ?thesis"
apply (insert sdiv_int_range [where a="sint a" and b="sint b"])
apply (clarsimp simp: word_size sint_int_min)
done
show ?thesis
apply (rule UnE [OF result_range result_range_simple])
apply simp
apply (clarsimp simp: word_size)
using result_range_overflow
apply (clarsimp simp: word_size)
done
qed
lemmas sdiv_word_min' = sdiv_word_min [simplified word_size, simplified]
lemmas sdiv_word_max' = sdiv_word_max [simplified word_size, simplified]
lemma signed_arith_ineq_checks_to_eq:
"((- (2 ^ (size a - 1)) ≤ (sint a + sint b)) ∧ (sint a + sint b ≤ (2 ^ (size a - 1) - 1)))
= (sint a + sint b = sint (a + b ))"
"((- (2 ^ (size a - 1)) ≤ (sint a - sint b)) ∧ (sint a - sint b ≤ (2 ^ (size a - 1) - 1)))
= (sint a - sint b = sint (a - b))"
"((- (2 ^ (size a - 1)) ≤ (- sint a)) ∧ (- sint a) ≤ (2 ^ (size a - 1) - 1))
= ((- sint a) = sint (- a))"
"((- (2 ^ (size a - 1)) ≤ (sint a * sint b)) ∧ (sint a * sint b ≤ (2 ^ (size a - 1) - 1)))
= (sint a * sint b = sint (a * b))"
"((- (2 ^ (size a - 1)) ≤ (sint a sdiv sint b)) ∧ (sint a sdiv sint b ≤ (2 ^ (size a - 1) - 1)))
= (sint a sdiv sint b = sint (a sdiv b))"
"((- (2 ^ (size a - 1)) ≤ (sint a smod sint b)) ∧ (sint a smod sint b ≤ (2 ^ (size a - 1) - 1)))
= (sint a smod sint b = sint (a smod b))"
by (auto simp: sint_word_ariths word_size signed_div_arith signed_mod_arith signed_take_bit_int_eq_self_iff intro: sym dest: sym)
lemma signed_arith_sint:
"((- (2 ^ (size a - 1)) ≤ (sint a + sint b)) ∧ (sint a + sint b ≤ (2 ^ (size a - 1) - 1)))
⟹ sint (a + b) = (sint a + sint b)"
"((- (2 ^ (size a - 1)) ≤ (sint a - sint b)) ∧ (sint a - sint b ≤ (2 ^ (size a - 1) - 1)))
⟹ sint (a - b) = (sint a - sint b)"
"((- (2 ^ (size a - 1)) ≤ (- sint a)) ∧ (- sint a) ≤ (2 ^ (size a - 1) - 1))
⟹ sint (- a) = (- sint a)"
"((- (2 ^ (size a - 1)) ≤ (sint a * sint b)) ∧ (sint a * sint b ≤ (2 ^ (size a - 1) - 1)))
⟹ sint (a * b) = (sint a * sint b)"
"((- (2 ^ (size a - 1)) ≤ (sint a sdiv sint b)) ∧ (sint a sdiv sint b ≤ (2 ^ (size a - 1) - 1)))
⟹ sint (a sdiv b) = (sint a sdiv sint b)"
"((- (2 ^ (size a - 1)) ≤ (sint a smod sint b)) ∧ (sint a smod sint b ≤ (2 ^ (size a - 1) - 1)))
⟹ sint (a smod b) = (sint a smod sint b)"
by (subst (asm) signed_arith_ineq_checks_to_eq; simp)+
lemma nasty_split_lt:
‹x * 2 ^ n + (2 ^ n - 1) ≤ 2 ^ m - 1›
if ‹x < 2 ^ (m - n)› ‹n ≤ m› ‹m < LENGTH('a::len)›
for x :: ‹'a::len word›
proof -
define q where ‹q = m - n›
with ‹n ≤ m› have ‹m = q + n›
by simp
with ‹x < 2 ^ (m - n)› have *: ‹i < q› if ‹bit x i› for i
using that by simp (metis bit_take_bit_iff take_bit_word_eq_self_iff)
from ‹m = q + n› have ‹push_bit n x OR mask n ≤ mask m›
by (auto simp add: le_mask_high_bits word_size bit_simps dest!: *)
then have ‹push_bit n x + mask n ≤ mask m›
by (simp add: disjunctive_add bit_simps)
then show ?thesis
by (simp add: mask_eq_exp_minus_1 push_bit_eq_mult)
qed
lemma nasty_split_less:
"⟦m ≤ n; n ≤ nm; nm < LENGTH('a::len); x < 2 ^ (nm - n)⟧
⟹ (x :: 'a word) * 2 ^ n + (2 ^ m - 1) < 2 ^ nm"
apply (simp only: word_less_sub_le[symmetric])
apply (rule order_trans [OF _ nasty_split_lt])
apply (rule word_plus_mono_right)
apply (rule word_sub_mono)
apply (simp add: word_le_nat_alt)
apply simp
apply (simp add: word_sub_1_le[OF power_not_zero])
apply (simp add: word_sub_1_le[OF power_not_zero])
apply (rule is_aligned_no_wrap')
apply (rule is_aligned_mult_triv2)
apply simp
apply (erule order_le_less_trans, simp)
apply simp+
done
end
end