/*
 * Copyright (C) 2006 Apple Computer, Inc. All rights reserved.
 *
 * This document is the property of Apple Computer, Inc.
 * It is considered confidential and proprietary.
 *
 * This document may not be reproduced or transmitted in any form,
 * in whole or in part, without the express written permission of
 * Apple Computer, Inc.
 */
	.text
	.align 2

	.globl _strlen
/* int strlen(const char *s); */
_strlen:
	/* save the original pointer */
	mov		r12, r0

	/* see if the string is aligned */
	ands	r3, r0, #3

	/* load the first word, address rounded down */
	bic		r0, r0, #3
	ldr		r2, [r0], #4

	/* skip the next part if the string is already aligned */
	beq		Laligned

Lunaligned:
	/* unaligned pointer, mask out the bytes that we've read that we should be ignoring */
	cmp		r3, #2
	orr		r2, r2, #0x000000ff
	orrge	r2, r2, #0x0000ff00
	orrgt	r2, r2, #0x00ff0000

Laligned:
	/* load 0x01010101 into r1 */
	mov		r1, #0x01
	orr		r1, r1, r1, lsl #8
	orr		r1, r1, r1, lsl #16

Laligned_loop:
	/* ((x - 0x01010101) & ~x & 0x80808080) == hasnull(word) */
	sub		r3, r2, r1		/* x - 0x01010101 */
	bic		r3, r3, r2		/* above & ~x */
	tst		r3, r1, lsl #7	/* above & 0x80808080 */
	ldreq	r2, [r0], #4	/* load next word */
	beq		Laligned_loop

	/* we found a nullbyte */
	/* r0 (ptr) has overshot by up to 4 bytes, so subtract off until we find a nullbyte */
	sub		r0, r0, #1
	tst		r2, #0x000000ff
	subeq	r0, r0, #1
	tstne	r2, #0x0000ff00
	subeq	r0, r0, #1
	tstne	r2, #0x00ff0000
	subeq	r0, r0, #1

Lexit:
	/* len = ptr - original pointer */
	sub		r0, r0, r12
	bx		lr