strlen.S 3.5 KB

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  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 <features.h>
  17. #include <endian.h>
  18. #include <sys/syscall.h>
  19. #include <bits/arm_asm.h>
  20. /* size_t strlen(const char *S)
  21. * entry: r0 -> string
  22. * exit: r0 = len
  23. */
  24. .text
  25. .global strlen
  26. .type strlen,%function
  27. .align 4
  28. #if defined(THUMB1_ONLY)
  29. /* A simple implementation for when the ARM implementation can't be used. */
  30. .thumb_func
  31. strlen:
  32. mov r2, #0
  33. 1:
  34. ldrb r1, [r0, r2]
  35. add r2, r2, #1
  36. cmp r1, #0
  37. bne 1b
  38. sub r0, r2, #1
  39. bx lr
  40. #else
  41. strlen:
  42. bic r1, r0, $3 @ addr of word containing first byte
  43. ldr r2, [r1], $4 @ get the first word
  44. ands r3, r0, $3 @ how many bytes are duff?
  45. rsb r0, r3, $0 @ get - that number into counter.
  46. beq Laligned @ skip into main check routine if no
  47. @ more
  48. #if __BYTE_ORDER == __BIG_ENDIAN
  49. orr r2, r2, $0xff000000 @ set this byte to non-zero
  50. subs r3, r3, $1 @ any more to do?
  51. IT(t, gt)
  52. orrgt r2, r2, $0x00ff0000 @ if so, set this byte
  53. subs r3, r3, $1 @ more?
  54. IT(t, gt)
  55. orrgt r2, r2, $0x0000ff00 @ then set.
  56. #else
  57. orr r2, r2, $0x000000ff @ set this byte to non-zero
  58. subs r3, r3, $1 @ any more to do?
  59. IT(t, gt)
  60. orrgt r2, r2, $0x0000ff00 @ if so, set this byte
  61. subs r3, r3, $1 @ more?
  62. IT(t, gt)
  63. orrgt r2, r2, $0x00ff0000 @ then set.
  64. #endif
  65. Laligned: @ here, we have a word in r2. Does it
  66. tst r2, $0x000000ff @ contain any zeroes?
  67. IT(tttt, ne)
  68. tstne r2, $0x0000ff00 @
  69. tstne r2, $0x00ff0000 @
  70. tstne r2, $0xff000000 @
  71. addne r0, r0, $4 @ if not, the string is 4 bytes longer
  72. IT(t, ne)
  73. ldrne r2, [r1], $4 @ and we continue to the next word
  74. bne Laligned @
  75. Llastword: @ drop through to here once we find a
  76. #if __BYTE_ORDER == __BIG_ENDIAN
  77. tst r2, $0xff000000 @ word that has a zero byte in it
  78. IT(tttt, ne)
  79. addne r0, r0, $1 @
  80. tstne r2, $0x00ff0000 @ and add up to 3 bytes on to it
  81. addne r0, r0, $1 @
  82. tstne r2, $0x0000ff00 @ (if first three all non-zero, 4th
  83. IT(t, ne)
  84. addne r0, r0, $1 @ must be zero)
  85. #else
  86. tst r2, $0x000000ff @
  87. IT(tttt, ne)
  88. addne r0, r0, $1 @
  89. tstne r2, $0x0000ff00 @ and add up to 3 bytes on to it
  90. addne r0, r0, $1 @
  91. tstne r2, $0x00ff0000 @ (if first three all non-zero, 4th
  92. IT(t, ne)
  93. addne r0, r0, $1 @ must be zero)
  94. #endif
  95. #if defined(__USE_BX__)
  96. bx lr
  97. #else
  98. mov pc,lr
  99. #endif
  100. #endif
  101. .size strlen,.-strlen
  102. libc_hidden_def(strlen)