/* strlen -- find the length of a nul-terminated string.

   Copyright (C) 2013-2018 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

	ldrb	r2, [r0]		@ 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:	ldrb	r2, [r0, #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.

	ldrd	r2, r3, [r0], #8

#ifdef ARCH_HAS_T2

	movw	ip, #0x0101

	pld	[r0, #64]

	movt	ip, #0x0101

#else

	ldr	ip, =0x01010101

	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

	pld	[r0, #128]		@ Prefetch 2 lines ahead

	orrs	r3, r3, r2		@ Combine the two words

	it	eq

	ldrdeq	r2, r3, [r0], #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)