strlen.S 2.8 KB

1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071
  1. /* Copyright (C) 1998 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. The GNU C Library is free software; you can redistribute it and/or
  5. modify it under the terms of the GNU Lesser General Public
  6. License as published by the Free Software Foundation; either
  7. version 2.1 of the License, or (at your option) any later version.
  8. The GNU C Library is distributed in the hope that it will be useful,
  9. but WITHOUT ANY WARRANTY; without even the implied warranty of
  10. MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  11. Lesser General Public License for more details.
  12. You should have received a copy of the GNU Lesser General Public
  13. License along with the GNU C Library; if not, write to the Free
  14. Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  15. 02111-1307 USA. */
  16. #include <endian.h>
  17. #include <sys/syscall.h>
  18. /* size_t strlen(const char *S)
  19. * entry: r0 -> string
  20. * exit: r0 = len
  21. */
  22. .text
  23. .global strlen;
  24. .type strlen,%function
  25. .align 4; \
  26. strlen:
  27. bic r1, r0, $3 @ addr of word containing first byte
  28. ldr r2, [r1], $4 @ get the first word
  29. ands r3, r0, $3 @ how many bytes are duff?
  30. rsb r0, r3, $0 @ get - that number into counter.
  31. beq Laligned @ skip into main check routine if no
  32. @ more
  33. #if __BYTE_ORDER == __BIG_ENDIAN
  34. orr r2, r2, $0xff000000 @ set this byte to non-zero
  35. subs r3, r3, $1 @ any more to do?
  36. orrgt r2, r2, $0x00ff0000 @ if so, set this byte
  37. subs r3, r3, $1 @ more?
  38. orrgt r2, r2, $0x0000ff00 @ then set.
  39. #else
  40. orr r2, r2, $0x000000ff @ set this byte to non-zero
  41. subs r3, r3, $1 @ any more to do?
  42. orrgt r2, r2, $0x0000ff00 @ if so, set this byte
  43. subs r3, r3, $1 @ more?
  44. orrgt r2, r2, $0x00ff0000 @ then set.
  45. #endif
  46. Laligned: @ here, we have a word in r2. Does it
  47. tst r2, $0x000000ff @ contain any zeroes?
  48. tstne r2, $0x0000ff00 @
  49. tstne r2, $0x00ff0000 @
  50. tstne r2, $0xff000000 @
  51. addne r0, r0, $4 @ if not, the string is 4 bytes longer
  52. ldrne r2, [r1], $4 @ and we continue to the next word
  53. bne Laligned @
  54. Llastword: @ drop through to here once we find a
  55. tst r2, $0x000000ff @ word that has a zero byte in it
  56. addne r0, r0, $1 @
  57. tstne r2, $0x0000ff00 @ and add up to 3 bytes on to it
  58. addne r0, r0, $1 @
  59. tstne r2, $0x00ff0000 @ (if first three all non-zero, 4th
  60. addne r0, r0, $1 @ must be zero)
  61. mov pc,lr
  62. .size strlen,.-strlen;