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torvalds
GitHub Repository: torvalds/linux
 Path: blob/master/arch/arc/lib/strcmp.S
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/* SPDX-License-Identifier: GPL-2.0-only */

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/*

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 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)

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 */

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/* This is optimized primarily for the ARC700.

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   It would be possible to speed up the loops by one cycle / word

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   respective one cycle / byte by forcing double source 1 alignment, unrolling

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   by a factor of two, and speculatively loading the second word / byte of

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   source 1; however, that would increase the overhead for loop setup / finish,

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   and strcmp might often terminate early.  */

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#include <linux/linkage.h>

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ENTRY_CFI(strcmp)

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	or	r2,r0,r1

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	bmsk_s	r2,r2,1

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	brne	r2,0,.Lcharloop

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	mov_s	r12,0x01010101

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	ror	r5,r12

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.Lwordloop:

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	ld.ab	r2,[r0,4]

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	ld.ab	r3,[r1,4]

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	nop_s

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	sub	r4,r2,r12

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	bic	r4,r4,r2

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	and	r4,r4,r5

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	brne	r4,0,.Lfound0

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	breq	r2,r3,.Lwordloop

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#ifdef	__LITTLE_ENDIAN__

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	xor	r0,r2,r3	; mask for difference

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	sub_s	r1,r0,1

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	bic_s	r0,r0,r1	; mask for least significant difference bit

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	sub	r1,r5,r0

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	xor	r0,r5,r1	; mask for least significant difference byte

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	and_s	r2,r2,r0

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	and_s	r3,r3,r0

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#endif /* LITTLE ENDIAN */

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	cmp_s	r2,r3

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	mov_s	r0,1

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	j_s.d	[blink]

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	bset.lo	r0,r0,31

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	.balign	4

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#ifdef __LITTLE_ENDIAN__

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.Lfound0:

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	xor	r0,r2,r3	; mask for difference

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	or	r0,r0,r4	; or in zero indicator

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	sub_s	r1,r0,1

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	bic_s	r0,r0,r1	; mask for least significant difference bit

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	sub	r1,r5,r0

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	xor	r0,r5,r1	; mask for least significant difference byte

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	and_s	r2,r2,r0

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	and_s	r3,r3,r0

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	sub.f	r0,r2,r3

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	mov.hi	r0,1

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	j_s.d	[blink]

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	bset.lo	r0,r0,31

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#else /* BIG ENDIAN */

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	/* The zero-detection above can mis-detect 0x01 bytes as zeroes

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	   because of carry-propagateion from a lower significant zero byte.

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	   We can compensate for this by checking that bit0 is zero.

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	   This compensation is not necessary in the step where we

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	   get a low estimate for r2, because in any affected bytes

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	   we already have 0x00 or 0x01, which will remain unchanged

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	   when bit 7 is cleared.  */

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	.balign	4

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.Lfound0:

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	lsr	r0,r4,8

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	lsr_s	r1,r2

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	bic_s	r2,r2,r0	; get low estimate for r2 and get ...

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	bic_s	r0,r0,r1	; <this is the adjusted mask for zeros>

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	or_s	r3,r3,r0	; ... high estimate r3 so that r2 > r3 will ...

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	cmp_s	r3,r2		; ... be independent of trailing garbage

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	or_s	r2,r2,r0	; likewise for r3 > r2

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	bic_s	r3,r3,r0

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	rlc	r0,0		; r0 := r2 > r3 ? 1 : 0

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	cmp_s	r2,r3

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	j_s.d	[blink]

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	bset.lo	r0,r0,31

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#endif /* ENDIAN */

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	.balign	4

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.Lcharloop:

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	ldb.ab	r2,[r0,1]

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	ldb.ab	r3,[r1,1]

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	nop_s

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	breq	r2,0,.Lcmpend

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	breq	r2,r3,.Lcharloop

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.Lcmpend:

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	j_s.d	[blink]

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	sub	r0,r2,r3

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END_CFI(strcmp)

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