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awilliam
GitHub Repository: awilliam/linux-vfio
 Path: blob/master/arch/cris/arch-v32/lib/checksumcopy.S
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/*

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 * A fast checksum+copy routine using movem

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 * Copyright (c) 1998-2007 Axis Communications AB

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 *

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 * Authors:	Bjorn Wesen

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 *

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 * csum_partial_copy_nocheck(const char *src, char *dst,

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 *		             int len, unsigned int sum)

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 */

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	.globl	csum_partial_copy_nocheck

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	.type   csum_partial_copy_nocheck,@function

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csum_partial_copy_nocheck:

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	;; r10 - src

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	;; r11 - dst

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	;; r12 - length

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	;; r13 - checksum

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	;; Optimized for large packets

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	subq	10*4, $r12

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	blt	_word_loop

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	move.d	$r12, $acr

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	subq	9*4,$sp

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	clearf	c

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	movem	$r8,[$sp]

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	;; do a movem copy and checksum

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1:	;; A failing userspace access (the read) will have this as PC.

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

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	addoq	-10*4, $acr, $acr ; loop counter in latency cycle

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	movem	$r9,[$r11+]	; write 10 longwords

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	;; perform dword checksumming on the 10 longwords

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	addc	$r0,$r13

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	addc	$r1,$r13

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	addc	$r2,$r13

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	addc	$r3,$r13

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	addc	$r4,$r13

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	addc	$r5,$r13

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	addc	$r6,$r13

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	addc	$r7,$r13

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	addc	$r8,$r13

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	addc	$r9,$r13

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	;; test $acr, without trashing carry.

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	move.d	$acr, $acr

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	bpl	_mloop

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	;; r12 <= acr  is needed after mloop and in the exception handlers.

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	move.d	$acr, $r12

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	;; fold the last carry into r13

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	addc	0, $r13

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

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_word_loop:

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	addq	10*4,$r12	; compensate for last loop underflowing length

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

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	;; r9 can be used as temporary.

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	move.d	$r13,$r9

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	lsrq	16,$r9		; r0 = checksum >> 16

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	and.d	0xffff,$r13	; checksum = checksum & 0xffff

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	subq	2, $r12

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	blt	_no_words

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	add.d	$r9,$r13	; checksum += r0

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	;; copy and checksum the rest of the words

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2:	;; A failing userspace access for the read below will have this as PC.

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_wloop:	move.w	[$r10+],$r9

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	addu.w	$r9,$r13

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	subq	2,$r12

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	bge	_wloop

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	move.w	$r9,[$r11+]

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_no_words:

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	addq	2,$r12

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	bne	_do_byte

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	nop

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	ret

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	move.d	$r13,$r10

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_do_byte:

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	;; copy and checksum the last byte

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3:	;; A failing userspace access for the read below will have this as PC.

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	move.b	[$r10],$r9

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	addu.b	$r9,$r13

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	move.b	$r9,[$r11]

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	ret

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	move.d	$r13,$r10

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	.size   csum_partial_copy_nocheck, . - csum_partial_copy_nocheck

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