contrib/loaders/checksum/mips32.s

   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  *   59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.             *
  19  ***************************************************************************/
  20
  21         .global main
  22         .text
  23         .set noreorder
  24
  25 /* params:
  26  * $a0 address in
  27  * $a1 byte count
  28  * vars
  29  * $a0 crc
  30  * $a1 crc data byte
  31  * temps:
  32  * t3 v0 a3 a2 t0 v1
  33  */
  34
  35 .ent main
  36 main:
  37         addiu   $t4, $a0, 0             /* address in */
  38         addiu   $t2, $a1, 0             /* count */
  39
  40         addiu   $a0, $zero, 0xffffffff /* a0 crc - result */
  41
  42         beq             $zero, $zero, ncomp
  43         addiu   $t3, $zero, 0   /* clear bytes read */
  44
  45 nbyte:
  46         lb              $a1, ($t4)              /* load byte from source address */
  47         addi    $t4, $t4, 1             /* inc byte count */
  48
  49 crc:
  50         sll             $a1, $a1, 24
  51         lui             $v0, 0x04c1
  52         xor             $a0, $a0, $a1
  53         ori             $a3, $v0, 0x1db7
  54         addu    $a2, $zero, $zero /* clear bit count */
  55 loop:
  56         sll             $t0, $a0, 1
  57         addiu   $a2, $a2, 1             /* inc bit count */
  58         slti    $a0, $a0, 0
  59         xor             $t1, $t0, $a3
  60         movn    $t0, $t1, $a0
  61         slti    $v1, $a2, 8             /* 8bits processed */
  62         bne             $v1, $zero, loop
  63         addu    $a0, $t0, $zero
  64
  65 ncomp:
  66         bne             $t2, $t3, nbyte /* all bytes processed */
  67         addiu   $t3, $t3, 1
  68
  69 wait:
  70         sdbbp
  71
  72 .end main