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awilliam
GitHub Repository: awilliam/linux-vfio
 Path: blob/master/arch/cris/arch-v10/lib/checksum.S
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/*

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 * A fast checksum routine using movem

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 * Copyright (c) 1998-2001 Axis Communications AB

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 *

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 * csum_partial(const unsigned char * buff, int len, unsigned int sum)

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 */

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	.globl	csum_partial

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csum_partial:

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	;; r10 - src

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	;; r11 - length

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	;; r12 - checksum

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	;; check for breakeven length between movem and normal word looping versions

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	;; we also do _NOT_ want to compute a checksum over more than the 

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	;; actual length when length < 40

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	cmpu.w	80,$r11

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	blo	_word_loop

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	nop

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	;; need to save the registers we use below in the movem loop

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	;; this overhead is why we have a check above for breakeven length

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	;; only r0 - r8 have to be saved, the other ones are clobber-able

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	;; according to the ABI

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	subq	9*4,$sp

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	movem	$r8,[$sp]

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	;; do a movem checksum

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	subq	10*4,$r11	; update length for the first loop

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_mloop:	movem	[$r10+],$r9	; read 10 longwords

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	;; perform dword checksumming on the 10 longwords

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	add.d	$r0,$r12

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	ax

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	add.d	$r1,$r12

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	ax

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	add.d	$r2,$r12

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	ax

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	add.d	$r3,$r12

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	ax

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	add.d	$r4,$r12

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	ax

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	add.d	$r5,$r12

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	ax

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	add.d	$r6,$r12

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	ax

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	add.d	$r7,$r12

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	ax

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	add.d	$r8,$r12

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	ax

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	add.d	$r9,$r12

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	;; fold the carry into the checksum, to avoid having to loop the carry

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	;; back into the top

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	ax

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	addq	0,$r12

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	subq	10*4,$r11

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	bge	_mloop

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	nop

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	addq	10*4,$r11	; compensate for last loop underflowing length

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	movem	[$sp+],$r8	; restore regs

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_word_loop:

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	;; only fold if there is anything to fold.

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	cmpq	0,$r12

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	beq	_no_fold

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	;; fold 32-bit checksum into a 16-bit checksum, to avoid carries below.

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	;; r9 and r13 can be used as temporaries.

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	moveq	-1,$r9		; put 0xffff in r9, faster than move.d 0xffff,r9

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	lsrq	16,$r9

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	move.d	$r12,$r13

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	lsrq	16,$r13		; r13 = checksum >> 16

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	and.d	$r9,$r12		; checksum = checksum & 0xffff

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	add.d	$r13,$r12		; checksum += r13

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_no_fold:

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	cmpq	2,$r11

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	blt	_no_words

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	nop

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	;; checksum the rest of the words

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	subq	2,$r11

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_wloop:	subq	2,$r11

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	bge	_wloop

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	addu.w	[$r10+],$r12

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	addq	2,$r11

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_no_words:

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	;; see if we have one odd byte more

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	cmpq	1,$r11

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	beq	_do_byte

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	nop

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	ret

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	move.d	$r12, $r10

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_do_byte:	

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	;; copy and checksum the last byte

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	addu.b	[$r10],$r12

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	ret

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	move.d	$r12, $r10

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