arm/string/strlen.s

   1 /*
   2  * Copyright (c) 2006 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  16  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  18  * Please see the License for the specific language governing rights and
  19  * limitations under the License.
  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23
  24 .text
  25         .align 2
  26
  27         .globl _strlen
  28 /* size_t strlen(const char *s); */
  29 _strlen:
  30         /* save the original pointer */
  31         mov             r12, r0
  32
  33         /* see if the string is aligned */
  34         ands    r3, r0, #3
  35
  36         /* load the first word, address rounded down */
  37         bic             r0, r0, #3
  38         ldr             r2, [r0], #4
  39
  40         /* skip the next part if the string is already aligned */
  41         beq             Laligned
  42
  43 Lunaligned:
  44         /* unaligned pointer, mask out the bytes that we've read that we should be ignoring */
  45         cmp             r3, #2
  46         orr             r2, r2, #0x000000ff
  47         orrge   r2, r2, #0x0000ff00
  48         orrgt   r2, r2, #0x00ff0000
  49
  50 Laligned:
  51         /* load 0x01010101 into r1 */
  52         mov             r1, #0x01
  53         orr             r1, r1, r1, lsl #8
  54         orr             r1, r1, r1, lsl #16
  55
  56 Laligned_loop:
  57         /* ((x - 0x01010101) & ~x & 0x80808080) == hasnull(word) */
  58         sub             r3, r2, r1              /* x - 0x01010101 */
  59         bic             r3, r3, r2              /* above & ~x */
  60         tst             r3, r1, lsl #7  /* above & 0x80808080 */
  61         ldreq   r2, [r0], #4    /* load next word */
  62         beq             Laligned_loop
  63
  64         /* we found a nullbyte */
  65         /* r0 (ptr) has overshot by up to 4 bytes, so subtract off until we find a nullbyte */
  66         sub             r0, r0, #1
  67         tst             r2, #0x000000ff
  68         subeq   r0, r0, #1
  69         tstne   r2, #0x0000ff00
  70         subeq   r0, r0, #1
  71         tstne   r2, #0x00ff0000
  72         subeq   r0, r0, #1
  73
  74 Lexit:
  75         /* len = ptr - original pointer */
  76         sub             r0, r0, r12
  77         bx              lr
  78