[thirdparty/glibc.git] / ports / sysdeps / arm / armv6 / strlen.S

/* strlen -- find the length of a nul-terminated string.
   Copyright (C) 2013-2014 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   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>

	.syntax unified
	.text

ENTRY (strlen)
	@ r0 = start of string
	sfi_breg r0, \
	ldrb	r2, [\B]		@ load the first byte asap

	@ To cater to long strings, we want to search through a few
	@ characters until we reach an aligned pointer.  To cater to
	@ small strings, we don't want to start doing word operations
	@ immediately.  The compromise is a maximum of 16 bytes less
	@ whatever is required to end with an aligned pointer.
	@ r3 = number of characters to search in alignment loop
	and	r3, r0, #7
	mov	r1, r0			@ Save the input pointer
	rsb	r3, r3, #15		@ 16 - 1 peeled loop iteration
	cmp	r2, #0
	beq	99f

	@ Loop until we find ...
1:	sfi_breg r0, \
	ldrb	r2, [\B, #1]!
	subs	r3, r3, #1		@ ... the aligment point
	it	ne
	cmpne	r2, #0			@ ... or EOS
	bne	1b

	@ Disambiguate the exit possibilites above
	cmp	r2, #0			@ Found EOS
	beq	99f
	add	r0, r0, #1

	@ So now we're aligned.
	sfi_breg r0, \
	ldrd	r2, r3, [\B], #8
#ifdef ARCH_HAS_T2
	movw	ip, #0x0101
	sfi_pld	r0, #64
	movt	ip, #0x0101
#else
	ldr	ip, =0x01010101
	sfi_pld	r0, #64
#endif

	@ Loop searching for EOS, 8 bytes at a time.
	@ Subtracting (unsigned saturating) from 1 for any byte means that
	@ we get 1 for any byte that was originally zero and 0 otherwise.
	@ Therefore we consider the lsb of each byte the "found" bit.
	.balign	16
2:	uqsub8	r2, ip, r2		@ Find EOS
	uqsub8	r3, ip, r3
	sfi_pld	r0, #128		@ Prefetch 2 lines ahead
	orrs	r3, r3, r2		@ Combine the two words
	it	eq
	sfi_breg r0, \
	ldrdeq	r2, r3, [\B], #8
	beq	2b

	@ Found something.  Disambiguate between first and second words.
	@ Adjust r0 to point to the word containing the match.
	@ Adjust r2 to the found bits for the word containing the match.
	cmp	r2, #0
	sub	r0, r0, #4
	ite	eq
	moveq	r2, r3
	subne	r0, r0, #4

	@ Find the bit-offset of the match within the word.  Note that the
	@ bit result from clz will be 7 higher than "true", but we'll
	@ immediately discard those bits converting to a byte offset.
#ifdef __ARMEL__
	rev	r2, r2			@ For LE, count from the little end
#endif
	clz	r2, r2
	add	r0, r0, r2, lsr #3	@ Adjust the pointer to the found byte
99:
	sub	r0, r0, r1		@ Subtract input to compute length
	bx	lr

END (strlen)

libc_hidden_builtin_def (strlen)
Commit	Line	Data
f5ad94e0	1	/* strlen -- find the length of a nul-terminated string.
d4697bc9	2	Copyright (C) 2013-2014 Free Software Foundation, Inc.
f5ad94e0 RH	3	This file is part of the GNU C Library.
	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
	16	License along with the GNU C Library. If not, see
	17	<http://www.gnu.org/licenses/>. */
	18
	19	#include <sysdep.h>
	20
	21	.syntax unified
	22	.text
	23
	24	ENTRY (strlen)
	25	@ r0 = start of string
a7ac7522 RM	26	sfi_breg r0, \
a7ac7522 RM	27	ldrb r2, [\B] @ load the first byte asap
f5ad94e0 RH	28
	29	@ To cater to long strings, we want to search through a few
	30	@ characters until we reach an aligned pointer. To cater to
	31	@ small strings, we don't want to start doing word operations
	32	@ immediately. The compromise is a maximum of 16 bytes less
	33	@ whatever is required to end with an aligned pointer.
	34	@ r3 = number of characters to search in alignment loop
	35	and r3, r0, #7
	36	mov r1, r0 @ Save the input pointer
	37	rsb r3, r3, #15 @ 16 - 1 peeled loop iteration
	38	cmp r2, #0
	39	beq 99f
	40
	41	@ Loop until we find ...
a7ac7522 RM	42	1: sfi_breg r0, \
a7ac7522 RM	43	ldrb r2, [\B, #1]!
f5ad94e0 RH	44	subs r3, r3, #1 @ ... the aligment point
	45	it ne
	46	cmpne r2, #0 @ ... or EOS
	47	bne 1b
	48
	49	@ Disambiguate the exit possibilites above
	50	cmp r2, #0 @ Found EOS
	51	beq 99f
	52	add r0, r0, #1
	53
	54	@ So now we're aligned.
a7ac7522 RM	55	sfi_breg r0, \
a7ac7522 RM	56	ldrd r2, r3, [\B], #8
f5ad94e0 RH	57	#ifdef ARCH_HAS_T2
f5ad94e0 RH	58	movw ip, #0x0101
a7ac7522	59	sfi_pld r0, #64
f5ad94e0 RH	60	movt ip, #0x0101
	61	#else
	62	ldr ip, =0x01010101
a7ac7522	63	sfi_pld r0, #64
f5ad94e0 RH	64	#endif
	65
	66	@ Loop searching for EOS, 8 bytes at a time.
	67	@ Subtracting (unsigned saturating) from 1 for any byte means that
	68	@ we get 1 for any byte that was originally zero and 0 otherwise.
	69	@ Therefore we consider the lsb of each byte the "found" bit.
	70	.balign 16
	71	2: uqsub8 r2, ip, r2 @ Find EOS
	72	uqsub8 r3, ip, r3
a7ac7522	73	sfi_pld r0, #128 @ Prefetch 2 lines ahead
f5ad94e0 RH	74	orrs r3, r3, r2 @ Combine the two words
f5ad94e0 RH	75	it eq
a7ac7522 RM	76	sfi_breg r0, \
a7ac7522 RM	77	ldrdeq r2, r3, [\B], #8
f5ad94e0 RH	78	beq 2b
	79
	80	@ Found something. Disambiguate between first and second words.
	81	@ Adjust r0 to point to the word containing the match.
	82	@ Adjust r2 to the found bits for the word containing the match.
	83	cmp r2, #0
	84	sub r0, r0, #4
	85	ite eq
	86	moveq r2, r3
	87	subne r0, r0, #4
	88
	89	@ Find the bit-offset of the match within the word. Note that the
	90	@ bit result from clz will be 7 higher than "true", but we'll
	91	@ immediately discard those bits converting to a byte offset.
	92	#ifdef __ARMEL__
	93	rev r2, r2 @ For LE, count from the little end
	94	#endif
	95	clz r2, r2
	96	add r0, r0, r2, lsr #3 @ Adjust the pointer to the found byte
	97	99:
	98	sub r0, r0, r1 @ Subtract input to compute length
	99	bx lr
	100
	101	END (strlen)
	102
	103	libc_hidden_builtin_def (strlen)