# 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