66 lines
1.5 KiB
ArmAsm
66 lines
1.5 KiB
ArmAsm
|
/*
|
||
|
|
* 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
|
||
|
|
|