do_csum.S
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/* Optimised simple memory checksum
*
* Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/
#include <asm/cache.h>
.section .text
.balign L1_CACHE_BYTES
###############################################################################
#
# unsigned int do_csum(const unsigned char *buff, int len)
#
###############################################################################
.globl do_csum
.type do_csum,@function
do_csum:
movm [d2,d3],(sp)
mov d1,d2 # count
mov d0,a0 # buff
mov a0,a1
clr d1 # accumulator
cmp +0,d2
ble do_csum_done # check for zero length or negative
# 4-byte align the buffer pointer
btst +3,a0
beq do_csum_now_4b_aligned
btst +1,a0
beq do_csum_addr_not_odd
movbu (a0),d0
inc a0
asl +8,d0
add d0,d1
add -1,d2
do_csum_addr_not_odd:
cmp +2,d2
bcs do_csum_fewer_than_4
btst +2,a0
beq do_csum_now_4b_aligned
movhu (a0+),d0
add d0,d1
add -2,d2
cmp +4,d2
bcs do_csum_fewer_than_4
do_csum_now_4b_aligned:
# we want to checksum as much as we can in chunks of 32 bytes
cmp +31,d2
bls do_csum_remainder # 4-byte aligned remainder
add -32,d2
mov +32,d3
do_csum_loop:
mov (a0+),d0
mov (a0+),e0
mov (a0+),e1
mov (a0+),e3
add d0,d1
addc e0,d1
addc e1,d1
addc e3,d1
mov (a0+),d0
mov (a0+),e0
mov (a0+),e1
mov (a0+),e3
addc d0,d1
addc e0,d1
addc e1,d1
addc e3,d1
addc +0,d1
sub d3,d2
bcc do_csum_loop
add d3,d2
beq do_csum_done
do_csum_remainder:
# cut 16-31 bytes down to 0-15
cmp +16,d2
bcs do_csum_fewer_than_16
mov (a0+),d0
mov (a0+),e0
mov (a0+),e1
mov (a0+),e3
add d0,d1
addc e0,d1
addc e1,d1
addc e3,d1
addc +0,d1
add -16,d2
beq do_csum_done
do_csum_fewer_than_16:
# copy the remaining whole words
cmp +4,d2
bcs do_csum_fewer_than_4
cmp +8,d2
bcs do_csum_one_word
cmp +12,d2
bcs do_csum_two_words
mov (a0+),d0
add d0,d1
addc +0,d1
do_csum_two_words:
mov (a0+),d0
add d0,d1
addc +0,d1
do_csum_one_word:
mov (a0+),d0
add d0,d1
addc +0,d1
do_csum_fewer_than_4:
and +3,d2
beq do_csum_done
xor_cmp d0,d0,+2,d2
bcs do_csum_fewer_than_2
movhu (a0+),d0
and +1,d2
beq do_csum_add_last_bit
do_csum_fewer_than_2:
movbu (a0),d3
add d3,d0
do_csum_add_last_bit:
add d0,d1
addc +0,d1
do_csum_done:
# compress the checksum down to 16 bits
mov +0xffff0000,d0
and d1,d0
asl +16,d1
add d1,d0
addc +0xffff,d0
lsr +16,d0
# flip the halves of the word result if the buffer was oddly aligned
and +1,a1
beq do_csum_not_oddly_aligned
swaph d0,d0 # exchange bits 15:8 with 7:0
do_csum_not_oddly_aligned:
ret [d2,d3],8
.size do_csum, .-do_csum