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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_strfnd
zap_strfnd:
# Address of the first character:
#define start %rdi
# Character to be found:
#define cmp %sil
# Address of the current character:
#define addr %rax
# Current character:
#define chr %dl
movq start,addr # addr = start
# Iterate over the string:
.loop:
# Copy the character into a register:
movb (addr),chr # chr = *addr
# Check if we have found the character:
cmpb chr,cmp # if (chr == cmp)
je .fnd # goto fnd
# Check if we have found the null-terminator:
testb chr,chr # if (chr == 0x0)
jz .nfnd # goto nfnd
# Continue to the next character:
incq addr # ++addr
jmp .loop # goto loop
# Found:
.fnd:
# Get the offset of the character:
subq start,addr # addr -= start
ret # return addr
# Not found:
.nfnd:
movq $0xFFFFFFFFFFFFFFFF,addr # addr = 0xFFFFFFFFFFFFFFFF
ret # return addr
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