csumpartial.S
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/*
* linux/arch/arm/lib/csumpartial.S
*
* Copyright (C) 1995-1998 Russell King
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/linkage.h>
#include <asm/assembler.h>
.text
/*
* Function: __u32 csum_partial(const char *src, int len, __u32 sum)
* Params : r0 = buffer, r1 = len, r2 = checksum
* Returns : r0 = new checksum
*/
buf .req r0
len .req r1
sum .req r2
td0 .req r3
td1 .req r4 @ save before use
td2 .req r5 @ save before use
td3 .req lr
.Lzero: mov r0, sum
add sp, sp, #4
ldr pc, [sp], #4
/*
* Handle 0 to 7 bytes, with any alignment of source and
* destination pointers. Note that when we get here, C = 0
*/
.Lless8: teq len, #0 @ check for zero count
beq .Lzero
/* we must have at least one byte. */
tst buf, #1 @ odd address?
movne sum, sum, ror #8
ldrneb td0, [buf], #1
subne len, len, #1
adcnes sum, sum, td0, put_byte_1
.Lless4: tst len, #6
beq .Lless8_byte
/* we are now half-word aligned */
.Lless8_wordlp:
#if __LINUX_ARM_ARCH__ >= 4
ldrh td0, [buf], #2
sub len, len, #2
#else
ldrb td0, [buf], #1
ldrb td3, [buf], #1
sub len, len, #2
#ifndef __ARMEB__
orr td0, td0, td3, lsl #8
#else
orr td0, td3, td0, lsl #8
#endif
#endif
adcs sum, sum, td0
tst len, #6
bne .Lless8_wordlp
.Lless8_byte: tst len, #1 @ odd number of bytes
ldrneb td0, [buf], #1 @ include last byte
adcnes sum, sum, td0, put_byte_0 @ update checksum
.Ldone: adc r0, sum, #0 @ collect up the last carry
ldr td0, [sp], #4
tst td0, #1 @ check buffer alignment
movne r0, r0, ror #8 @ rotate checksum by 8 bits
ldr pc, [sp], #4 @ return
.Lnot_aligned: tst buf, #1 @ odd address
ldrneb td0, [buf], #1 @ make even
subne len, len, #1
adcnes sum, sum, td0, put_byte_1 @ update checksum
tst buf, #2 @ 32-bit aligned?
#if __LINUX_ARM_ARCH__ >= 4
ldrneh td0, [buf], #2 @ make 32-bit aligned
subne len, len, #2
#else
ldrneb td0, [buf], #1
ldrneb ip, [buf], #1
subne len, len, #2
#ifndef __ARMEB__
orrne td0, td0, ip, lsl #8
#else
orrne td0, ip, td0, lsl #8
#endif
#endif
adcnes sum, sum, td0 @ update checksum
mov pc, lr
ENTRY(csum_partial)
stmfd sp!, {buf, lr}
cmp len, #8 @ Ensure that we have at least
blo .Lless8 @ 8 bytes to copy.
tst buf, #1
movne sum, sum, ror #8
adds sum, sum, #0 @ C = 0
tst buf, #3 @ Test destination alignment
blne .Lnot_aligned @ align destination, return here
1: bics ip, len, #31
beq 3f
stmfd sp!, {r4 - r5}
2: ldmia buf!, {td0, td1, td2, td3}
adcs sum, sum, td0
adcs sum, sum, td1
adcs sum, sum, td2
adcs sum, sum, td3
ldmia buf!, {td0, td1, td2, td3}
adcs sum, sum, td0
adcs sum, sum, td1
adcs sum, sum, td2
adcs sum, sum, td3
sub ip, ip, #32
teq ip, #0
bne 2b
ldmfd sp!, {r4 - r5}
3: tst len, #0x1c @ should not change C
beq .Lless4
4: ldr td0, [buf], #4
sub len, len, #4
adcs sum, sum, td0
tst len, #0x1c
bne 4b
b .Lless4
ENDPROC(csum_partial)