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  1. /***************************************************************************
  2. * Copyright (C) 2010 by Spencer Oliver *
  3. * spen@spen-soft.co.uk *
  4. * *
  5. * This program is free software; you can redistribute it and/or modify *
  6. * it under the terms of the GNU General Public License as published by *
  7. * the Free Software Foundation; either version 2 of the License, or *
  8. * (at your option) any later version. *
  9. * *
  10. * This program 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 *
  13. * GNU General Public License for more details. *
  14. * *
  15. * You should have received a copy of the GNU General Public License *
  16. * along with this program; if not, write to the *
  17. * Free Software Foundation, Inc., *
  18. * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. *
  19. ***************************************************************************/
  20. .global main
  21. .text
  22. .set noreorder
  23. /* params:
  24. * $a0 address in
  25. * $a1 byte count
  26. * vars
  27. * $a0 crc
  28. * $a1 crc data byte
  29. * temps:
  30. * t3 v0 a3 a2 t0 v1
  31. */
  32. .ent main
  33. main:
  34. addiu $t4, $a0, 0 /* address in */
  35. addiu $t2, $a1, 0 /* count */
  36. addiu $a0, $zero, 0xffffffff /* a0 crc - result */
  37. beq $zero, $zero, ncomp
  38. addiu $t3, $zero, 0 /* clear bytes read */
  39. nbyte:
  40. lb $a1, ($t4) /* load byte from source address */
  41. addi $t4, $t4, 1 /* inc byte count */
  42. crc:
  43. sll $a1, $a1, 24
  44. lui $v0, 0x04c1
  45. xor $a0, $a0, $a1
  46. ori $a3, $v0, 0x1db7
  47. addu $a2, $zero, $zero /* clear bit count */
  48. loop:
  49. sll $t0, $a0, 1
  50. addiu $a2, $a2, 1 /* inc bit count */
  51. slti $a0, $a0, 0
  52. xor $t1, $t0, $a3
  53. movn $t0, $t1, $a0
  54. slti $v1, $a2, 8 /* 8bits processed */
  55. bne $v1, $zero, loop
  56. addu $a0, $t0, $zero
  57. ncomp:
  58. bne $t2, $t3, nbyte /* all bytes processed */
  59. addiu $t3, $t3, 1
  60. wait:
  61. sdbbp
  62. .end main