sysdeps/arm/strlen.S

   1 /* Copyright (C) 1998, 2003 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Code contributed by Matthew Wilcox <willy@odie.barnet.ac.uk>
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <sysdep.h>
  21
  22 /* size_t strlen(const char *S)
  23  * entry: r0 -> string
  24  * exit: r0 = len
  25  */
  26
  27 ENTRY(strlen)
  28         bic     r1, r0, $3              @ addr of word containing first byte
  29         ldr     r2, [r1], $4            @ get the first word
  30         ands    r3, r0, $3              @ how many bytes are duff?
  31         rsb     r0, r3, $0              @ get - that number into counter.
  32         beq     Laligned                @ skip into main check routine if no
  33                                         @ more
  34 #ifdef __ARMEB__
  35         orr     r2, r2, $0xff000000     @ set this byte to non-zero
  36         subs    r3, r3, $1              @ any more to do?
  37         orrgt   r2, r2, $0x00ff0000     @ if so, set this byte
  38         subs    r3, r3, $1              @ more?
  39         orrgt   r2, r2, $0x0000ff00     @ then set.
  40 #else
  41         orr     r2, r2, $0x000000ff     @ set this byte to non-zero
  42         subs    r3, r3, $1              @ any more to do?
  43         orrgt   r2, r2, $0x0000ff00     @ if so, set this byte
  44         subs    r3, r3, $1              @ more?
  45         orrgt   r2, r2, $0x00ff0000     @ then set.
  46 #endif
  47 Laligned:                               @ here, we have a word in r2.  Does it
  48         tst     r2, $0x000000ff         @ contain any zeroes?
  49         tstne   r2, $0x0000ff00         @
  50         tstne   r2, $0x00ff0000         @
  51         tstne   r2, $0xff000000         @
  52         addne   r0, r0, $4              @ if not, the string is 4 bytes longer
  53         ldrne   r2, [r1], $4            @ and we continue to the next word
  54         bne     Laligned                @
  55 Llastword:                              @ drop through to here once we find a
  56 #ifdef __ARMEB__
  57         tst     r2, $0xff000000         @ word that has a zero byte in it
  58         addne   r0, r0, $1              @
  59         tstne   r2, $0x00ff0000         @ and add up to 3 bytes on to it
  60         addne   r0, r0, $1              @
  61         tstne   r2, $0x0000ff00         @ (if first three all non-zero, 4th
  62         addne   r0, r0, $1              @  must be zero)
  63 #else
  64         tst     r2, $0x000000ff         @ word that has a zero byte in it
  65         addne   r0, r0, $1              @
  66         tstne   r2, $0x0000ff00         @ and add up to 3 bytes on to it
  67         addne   r0, r0, $1              @
  68         tstne   r2, $0x00ff0000         @ (if first three all non-zero, 4th
  69         addne   r0, r0, $1              @  must be zero)
  70 #endif
  71         DO_RET(lr)
  72 END(strlen)
  73 libc_hidden_builtin_def (strlen)