# 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_strlen

zap_strlen:
# Address of the current character:
#define addr  %rax
# Address of the first character:
#define start %rdi
# Current character:
#define chr   %dl

	movq start,addr

	# Iterate over the string:
.loop:

	# Move the character into a register:
	movb (addr),chr # chr = *addr

	# Check if we have reached the null-terminator:
	testb chr,chr # if (chr == 0x0)
	jz .done      # goto done

	# Continue to the next character:
	incq addr # ++addr
	jmp .loop # goto loop

	# Done:
.done:

	# Get the length:
	subq start,addr # addr -= start

	ret # return addr