[thirdparty/glibc.git] / ports / sysdeps / arm / armv6t2 / memchr.S

/* Copyright (C) 2011 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Code contributed by Dave Gilbert <david.gilbert@linaro.org>

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library.  If not, see
   <http://www.gnu.org/licenses/>.  */

#include <sysdep.h>

@ This memchr routine is optimised on a Cortex-A9 and should work on all ARMv7
@ and ARMv6T2 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.
@ Note: The use of cbz/cbnz means it's Thumb only

@ 2011-07-15 david.gilbert@linaro.org
@    Copy from Cortex strings release 21 and change license
@ http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/view/head:/src/linaro-a9/memchr.S
@    Change function declarations/entry/exit
@ 2011-12-01 david.gilbert@linaro.org
@    Add some fixes from comments received (including use of ldrd instead ldm)
@ 2011-12-07 david.gilbert@linaro.org
@    Removed cbz from align loop - can't be taken

@ 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
	.syntax unified

	.text
	.thumb

@ ---------------------------------------------------------------------------
	.thumb_func
	.global memchr
	.type memchr,%function
ENTRY(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 think we can trust the caller to actually pass a char

	cmp	r2,#16		@ If it's 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
	bne	5b		@ If not aligned yet then do next byte

10:
	@ At this point, we are aligned, we know we have at least 8 bytes to work with
	push	{r4,r5,r6,r7}
	cfi_adjust_cfa_offset (16)
	cfi_rel_offset (r4, 0)
	cfi_rel_offset (r5, 4)
	cfi_rel_offset (r6, 8)
	cfi_rel_offset (r7, 12)

	cfi_remember_state

	orr	r1, r1, r1, lsl #8	@ expand the match word across to 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	@ Get it so that r5,r6 have 00's where the bytes match the target
	eor	r6,r6, r1
	uadd8	r5, r5, r7	@ Parallel add 0xff - sets the GE bits for anything that wasn't 0
	sel	r5, r3, r7	@ bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
	uadd8	r6, r6, r7	@ Parallel add 0xff - sets the GE bits for anything that wasn't 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) If not run out of bytes then go around again

	pop	{r4,r5,r6,r7}
	cfi_adjust_cfa_offset (-16)
	cfi_restore (r4)
	cfi_restore (r5)
	cfi_restore (r6)
	cfi_restore (r7)

	and	r1,r1,#0xff	@ Get r1 back to a single character from the expansion above
	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
	DO_RET(lr)

50:
	subs	r0,r0,#1	@ found
	DO_RET(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 that was tested
     @ r5 has the 00/ff pattern for the first word, r6 has the chained value
	cfi_restore_state
	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}
	cfi_adjust_cfa_offset (-16)
	cfi_restore (r4)
	cfi_restore (r5)
	cfi_restore (r6)
	cfi_restore (r7)

	subs	r0,r0,#1
	DO_RET(lr)

END(memchr)
libc_hidden_builtin_def (memchr)
Commit	Line	Data
b21cb02f DAG	1	/* Copyright (C) 2011 Free Software Foundation, Inc.
	2	This file is part of the GNU C Library.
	3	Code contributed by Dave Gilbert <david.gilbert@linaro.org>
	4
	5	The GNU C Library is free software; you can redistribute it and/or
	6	modify it under the terms of the GNU Lesser General Public
	7	License as published by the Free Software Foundation; either
	8	version 2.1 of the License, or (at your option) any later version.
	9
	10	The GNU C Library is distributed in the hope that it will be useful,
	11	but WITHOUT ANY WARRANTY; without even the implied warranty of
	12	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	13	Lesser General Public License for more details.
	14
	15	You should have received a copy of the GNU Lesser General Public
ab84e3ff PE	16	License along with the GNU C Library. If not, see
ab84e3ff PE	17	<http://www.gnu.org/licenses/>. */
b21cb02f DAG	18
	19	#include <sysdep.h>
	20
	21	@ This memchr routine is optimised on a Cortex-A9 and should work on all ARMv7
	22	@ and ARMv6T2 processors. It has a fast path for short sizes, and has an
	23	@ optimised path for large data sets; the worst case is finding the match early
	24	@ in a large data set.
	25	@ Note: The use of cbz/cbnz means it's Thumb only
	26
	27	@ 2011-07-15 david.gilbert@linaro.org
	28	@ Copy from Cortex strings release 21 and change license
	29	@ http://bazaar.launchpad.net/~linaro-toolchain-dev/cortex-strings/trunk/view/head:/src/linaro-a9/memchr.S
	30	@ Change function declarations/entry/exit
	31	@ 2011-12-01 david.gilbert@linaro.org
	32	@ Add some fixes from comments received (including use of ldrd instead ldm)
	33	@ 2011-12-07 david.gilbert@linaro.org
	34	@ Removed cbz from align loop - can't be taken
	35
	36	@ this lets us check a flag in a 00/ff byte easily in either endianness
	37	#ifdef __ARMEB__
	38	#define CHARTSTMASK(c) 1<<(31-(c*8))
	39	#else
	40	#define CHARTSTMASK(c) 1<<(c*8)
	41	#endif
	42	.syntax unified
	43
	44	.text
	45	.thumb
	46
	47	@ ---------------------------------------------------------------------------
	48	.thumb_func
	49	.global memchr
	50	.type memchr,%function
	51	ENTRY(memchr)
	52	@ r0 = start of memory to scan
	53	@ r1 = character to look for
	54	@ r2 = length
	55	@ returns r0 = pointer to character or NULL if not found
	56	and r1,r1,#0xff @ Don't think we can trust the caller to actually pass a char
	57
	58	cmp r2,#16 @ If it's short don't bother with anything clever
	59	blt 20f
	60
	61	tst r0, #7 @ If it's already aligned skip the next bit
	62	beq 10f
	63
	64	@ Work up to an aligned point
	65	5:
	66	ldrb r3, [r0],#1
	67	subs r2, r2, #1
	68	cmp r3, r1
	69	beq 50f @ If it matches exit found
	70	tst r0, #7
	71	bne 5b @ If not aligned yet then do next byte
	72
	73	10:
	74	@ At this point, we are aligned, we know we have at least 8 bytes to work with
	75	push {r4,r5,r6,r7}
	76	cfi_adjust_cfa_offset (16)
	77	cfi_rel_offset (r4, 0)
	78	cfi_rel_offset (r5, 4)
	79	cfi_rel_offset (r6, 8)
	80	cfi_rel_offset (r7, 12)
	81
82	cfi_remember_state
83
84	orr r1, r1, r1, lsl #8 @ expand the match word across to all bytes
85	orr r1, r1, r1, lsl #16
86	bic r4, r2, #7 @ Number of double words to work with * 8
87	mvns r7, #0 @ all F's
88	movs r3, #0
89
90	15:
91	ldrd r5,r6, [r0],#8
92	subs r4, r4, #8
93	eor r5,r5, r1 @ Get it so that r5,r6 have 00's where the bytes match the target
94	eor r6,r6, r1
95	uadd8 r5, r5, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0
96	sel r5, r3, r7 @ bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
97	uadd8 r6, r6, r7 @ Parallel add 0xff - sets the GE bits for anything that wasn't 0
98	sel r6, r5, r7 @ chained....bytes are 00 for none-00 bytes, or ff for 00 bytes - NOTE INVERSION
99	cbnz r6, 60f
100	bne 15b @ (Flags from the subs above) If not run out of bytes then go around again
101
102	pop {r4,r5,r6,r7}
103	cfi_adjust_cfa_offset (-16)
104	cfi_restore (r4)
105	cfi_restore (r5)
106	cfi_restore (r6)
107	cfi_restore (r7)
108
109	and r1,r1,#0xff @ Get r1 back to a single character from the expansion above
110	and r2,r2,#7 @ Leave the count remaining as the number after the double words have been done
111
112	20:
113	cbz r2, 40f @ 0 length or hit the end already then not found
114
115	21: @ Post aligned section, or just a short call
116	ldrb r3,[r0],#1
117	subs r2,r2,#1
118	eor r3,r3,r1 @ r3 = 0 if match - doesn't break flags from sub
119	cbz r3, 50f
120	bne 21b @ on r2 flags
121
122	40:
123	movs r0,#0 @ not found
124	DO_RET(lr)
125
126	50:
127	subs r0,r0,#1 @ found
128	DO_RET(lr)
129
130	60: @ We're here because the fast path found a hit - now we have to track down exactly which word it was
131	@ r0 points to the start of the double word after the one that was tested
132	@ r5 has the 00/ff pattern for the first word, r6 has the chained value
133	cfi_restore_state
134	cmp r5, #0
135	itte eq
136	moveq r5, r6 @ the end is in the 2nd word
137	subeq r0,r0,#3 @ Points to 2nd byte of 2nd word
138	subne r0,r0,#7 @ or 2nd byte of 1st word
139
140	@ r0 currently points to the 2nd byte of the word containing the hit
141	tst r5, # CHARTSTMASK(0) @ 1st character
142	bne 61f
143	adds r0,r0,#1
144	tst r5, # CHARTSTMASK(1) @ 2nd character
145	ittt eq
146	addeq r0,r0,#1
147	tsteq r5, # (3<<15) @ 2nd & 3rd character
148	@ If not the 3rd must be the last one
149	addeq r0,r0,#1
150
151	61:
152	pop {r4,r5,r6,r7}
153	cfi_adjust_cfa_offset (-16)
154	cfi_restore (r4)
155	cfi_restore (r5)
156	cfi_restore (r6)
157	cfi_restore (r7)
158
159	subs r0,r0,#1
160	DO_RET(lr)
161
162	END(memchr)
163	libc_hidden_builtin_def (memchr)