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# Copyright 2022 Gabriel Jensen.
# This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
# If a copy of the MPL was not distributed with this file, You can obtain one at https://mozilla.org/MPL/2.0/.
.globl zap_memeq
zap_memeq:
/* rdi: Left pointer. */
/* rsi: Number of remaining elements. */
/* rdx: Right pointer. */
/* rax: Current left element. */
/* rcx: Current right element. */
/* Compare words: */
.wrdcmp:
/* Check if there's at least one word left: */
cmpq $0x8,%rsi
jl .bytecmp /* If not, skip to byte checks: */
/* Copy the values into registers: */
movq (%rdi),%rax
movq (%rdx),%rcx
/* Check if the words are equal: */
cmpq %rax,%rcx
jne .neq
/* Mark eight more bytes as equal: */
addq $0x8,%rdi
addq $0x8,%rdx
subq $0x8,%rsi
/* Continue to the next word: */
jmp .wrdcmp
/* Compare bytes: */
.bytecmp:
/* Check if there are any bytes left: */
testq %rsi,%rsi
jz .eq /* If we have reached the final element, all previous elements have compared equal, and the memory sequences are equal. */
/* Copy the values into registers: */
movb (%rdi),%al
movb (%rdx),%cl
cmpb %al,%cl
jne .neq
/* Mark another byte as equal: */
incq %rdi
incq %rdx
decq %rsi
/* Continue to the next byte: */
jmp .bytecmp
/* The memory sequences have compared equal: */
.eq:
movb $0xFF,%al
ret
/* The memory sequences have compared NOT equal: */
.neq:
movb $0x0,%al
ret
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