path: root/zap/src/mem/strcp.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/.
*/

#include <zap/priv.h>

.globl zap_strcp

zap_strcp:

	/*
		char const * in
		char const * out
	*/

#if defined(__amd64__)

	# rax: Address of the current input character.
	# rdi: Address of the first input character.
	# rsi: Address of the current output character.
	# rdx: Current character.

	movq %rdi,%rax

	# Iterate over the strings:
.loop:

	# Copy character:
	movb (%rax),%dl # Move it into a register...
	movb %dl,(%rsi) # ... and then back into memory.

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

	# Continue to the next character:

	incq %rax
	incq %rsi
	jmp .loop

	# Finish:
.done:

	# Get the length of the (input) string:
	subq %rdi,%rax
	decq %rax # We do not count the null-terminator in the string length.

	ret

#endif