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/***************************************************************************
* Copyright (C) 2010 by Spencer Oliver *
* spen@spen-soft.co.uk *
* *
* This program is free software; you can redistribute it and/or modify *
* it under the terms of the GNU General Public License as published by *
* the Free Software Foundation; either version 2 of the License, or *
* (at your option) any later version. *
* *
* This program is distributed in the hope that it will be useful, *
* but WITHOUT ANY WARRANTY; without even the implied warranty of *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
* GNU General Public License for more details. *
* *
* You should have received a copy of the GNU General Public License *
* along with this program; if not, write to the *
* Free Software Foundation, Inc., *
* 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. *
***************************************************************************/
.global main
.text
.set noreorder
/* params:
* $a0 address in
* $a1 byte count
* vars
* $a0 crc
* $a1 crc data byte
* temps:
* t3 v0 a3 a2 t0 v1
*/
.ent main
main:
addiu $t4, $a0, 0 /* address in */
addiu $t2, $a1, 0 /* count */
addiu $a0, $zero, 0xffffffff /* a0 crc - result */
beq $zero, $zero, ncomp
addiu $t3, $zero, 0 /* clear bytes read */
nbyte:
lb $a1, ($t4) /* load byte from source address */
addi $t4, $t4, 1 /* inc byte count */
crc:
sll $a1, $a1, 24
lui $v0, 0x04c1
xor $a0, $a0, $a1
ori $a3, $v0, 0x1db7
addu $a2, $zero, $zero /* clear bit count */
loop:
sll $t0, $a0, 1
addiu $a2, $a2, 1 /* inc bit count */
slti $a0, $a0, 0
xor $t1, $t0, $a3
movn $t0, $t1, $a0
slti $v1, $a2, 8 /* 8bits processed */
bne $v1, $zero, loop
addu $a0, $t0, $zero
ncomp:
bne $t2, $t3, nbyte /* all bytes processed */
addiu $t3, $t3, 1
wait:
sdbbp
.end main
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