-# 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:

-# Left pointer:

-#define laddr %rdi

-# Number of remaining elements:

-#define rem %rsi

-# Right pointer:

-#define raddr %rdx

-# Current left element:

-#define lval8 %rax

-#define lval1 %al

-# Current right element:

-#define rval8 %rcx

-#define rval1 %cl

-

- # Compare words:

-.wrdcmp:

-

- # Check if there's at least one word left:

- cmpq $0x8,rem # if (rem == 8)

- jl .bytecmp # goto bytecmp

-

- # Copy the values into registers:

- movq (laddr),lval8 # lval8 = *laddr

- movq (raddr),rval8 # rval8 = *raddr

-

- # Check if the words are equal:

- cmpq lval8,rval8 # if (lval8 != rval8)

- jne .neq # goto neq

-

- # Mark eight more bytes as equal:

- addq $0x8,laddr # laddr += 0x8

- addq $0x8,raddr # raddr += 0x8

- subq $0x8,rem # rem -= 0x8

-

- # Continue to the next word:

- jmp .wrdcmp # goto wrdcmp

-

- # Compare bytes:

-.bytecmp:

-

- # Check if there are any bytes left:

- testq rem,rem # if (rem == 0x0)

- jz .eq # goto 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 (laddr),lval1 # lval1 = *laddr

- movb (raddr),rval1 # rval1 = *raddr

-

- cmpb lval1,rval1 # if (lval1 != rval1)

- jne .neq # goto neq

-

- # Mark another byte as equal:

- incq laddr # ++laddr

- incq raddr # ++raddr

- decq rem # --rem

-

- # Continue to the next byte:

- jmp .bytecmp # goto bytecmp

-

- # The memory sequences have compared equal:

-.eq:

- movb $0xFF,%al

- ret # return FF

-

- # The memory sequences have compared NOT equal:

-.neq:

- movb $0x0,%al

- ret # return 0