newlib-cygwin/newlib/libc/machine/arm/memchr.S

/* Copyright (c) 2010-2011, Linaro Limited
   All rights reserved.

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      * Neither the name of Linaro Limited nor the names of its
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   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
   HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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   Written by Dave Gilbert <david.gilbert@linaro.org>

   This memchr routine is optimised on a Cortex-A9 and should work on
   all ARMv7 processors.   It has a fast path for short sizes, and has
   an optimised path for large data sets; the worst case is finding the
   match early in a large data set. */

@ 2011-02-07 david.gilbert@linaro.org
@    Extracted from local git a5b438d861
@ 2011-07-14 david.gilbert@linaro.org
@    Import endianness fix from local git ea786f1b
@ 2011-10-11 david.gilbert@linaro.org
@    Import from cortex-strings bzr rev 63
@    Flip to ldrd (as suggested by Greta Yorsh)
@    Make conditional on CPU type
@    tidy

	.syntax unified
	.arch armv7-a

#include "arm_asm.h"

@ NOTE: This ifdef MUST match the one in memchr-stub.c
#if defined(_ISA_ARM_7) || defined(__ARM_ARCH_6T2__)

@ this lets us check a flag in a 00/ff byte easily in either endianness
#ifdef __ARMEB__
#define CHARTSTMASK(c) 1<<(31-(c*8))
#else
#define CHARTSTMASK(c) 1<<(c*8)
#endif
	.text
	.thumb

@ ---------------------------------------------------------------------------
	.thumb_func
	.align 2
	.p2align 4,,15
	.global memchr
	.type memchr,%function
memchr:
	@ r0 = start of memory to scan
	@ r1 = character to look for
	@ r2 = length
	@ returns r0 = pointer to character or NULL if not found
	and	r1,r1,#0xff	@ Don't trust the caller to pass a char

	cmp	r2,#16		@ If short don't bother with anything clever
	blt	20f 

	tst	r0, #7		@ If it's already aligned skip the next bit
	beq	10f

	@ Work up to an aligned point
5:
	ldrb	r3, [r0],#1
	subs	r2, r2, #1
	cmp	r3, r1
	beq	50f		@ If it matches exit found
	tst	r0, #7
	cbz	r2, 40f		@ If we run off the end, exit not found
	bne	5b		@ If not aligned yet then do next byte
	
10:
	@ We are aligned, we know we have at least 8 bytes to work with
	push	{r4,r5,r6,r7}
	orr	r1, r1, r1, lsl #8	@ expand the match word across all bytes
	orr	r1, r1, r1, lsl #16
	bic	r4, r2, #7	@ Number of double words to work with * 8
	mvns	r7, #0		@ all F's
	movs	r3, #0
	
15:
	ldrd    r5,r6,[r0],#8
	subs	r4, r4, #8
	eor	r5,r5, r1	@ r5,r6 have 00's where bytes match the target
	eor	r6,r6, r1
	uadd8	r5, r5, r7	@ Par add 0xff - sets GE bits for bytes!=0
	sel	r5, r3, r7	@ bytes are 00 for none-00 bytes,
				@ or ff for 00 bytes - NOTE INVERSION
	uadd8	r6, r6, r7	@ Par add 0xff - sets GE bits for bytes!=0
	sel	r6, r5, r7	@ chained....bytes are 00 for none-00 bytes
				@ or ff for 00 bytes - NOTE INVERSION
	cbnz	r6, 60f
	bne	15b		@ (Flags from the subs above)

	pop	{r4,r5,r6,r7}
	and	r1,r1,#0xff	@ r1 back to a single character
	and	r2,r2,#7	@ Leave the count remaining as the number
				@ after the double words have been done
 
20:
	cbz	r2, 40f		@ 0 length or hit the end already then not found

21:  @ Post aligned section, or just a short call
	ldrb	r3,[r0],#1
	subs	r2,r2,#1
	eor	r3,r3,r1	@ r3 = 0 if match - doesn't break flags from sub
	cbz	r3, 50f
	bne	21b		@ on r2 flags

40:
	movs	r0,#0		@ not found
	bx	lr

50:
	subs	r0,r0,#1	@ found
	bx	lr

60:  @ We're here because the fast path found a hit 
     @ now we have to track down exactly which word it was
	@ r0 points to the start of the double word after the one tested
	@ r5 has the 00/ff pattern for the first word, r6 has the chained value
	cmp	r5, #0
	itte	eq
	moveq	r5, r6		@ the end is in the 2nd word
	subeq	r0,r0,#3	@ Points to 2nd byte of 2nd word
	subne	r0,r0,#7	@ or 2nd byte of 1st word

	@ r0 currently points to the 2nd byte of the word containing the hit
	tst	r5, # CHARTSTMASK(0)	@ 1st character
	bne	61f
	adds	r0,r0,#1
	tst	r5, # CHARTSTMASK(1)	@ 2nd character
	ittt	eq
	addeq	r0,r0,#1
	tsteq	r5, # (3<<15)		@ 2nd & 3rd character
	@ If not the 3rd must be the last one
	addeq	r0,r0,#1

61:
	pop	{r4,r5,r6,r7}
	subs	r0,r0,#1
	bx	lr

#endif