path: root/zap/source/amd64/mem/fndchr.S

# 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_fndchr

zap_fndchr:
	# rdi: Address of the first character.
	# rsi: Character to be found.
	# rax: Address of the current character.
	# rdx: Current character.

	movq %rdi,%rax

	# Iterate over the string:
.loop:

	# Copy the character into a register:
	movb (%rax),%dl

	# Check if we have found the character:
	cmpb %dl,%sil
	je .fnd

	# Check if we have found the null-terminator:
	testb %dl,%dl
	jz .nfnd

	# Continue to the next character:
	incq %rax
	jmp .loop

	# Found:
.fnd:

	subq %rdi,%rax
	ret

	# Not found:
.nfnd:

	movq $0xFFFFFFFFFFFFFFFF,%rax
	ret