glibc/sysdeps/arm/armv6t2/strlen.S

/* Copyright (C) 2010-2020 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
   <https://www.gnu.org/licenses/>.  */

/*
   Assumes:
   ARMv6T2, AArch32

 */

#include <arm-features.h>
#include <sysdep.h>

#ifdef __ARMEB__
#define S2LO		lsl
#define S2HI		lsr
#else
#define S2LO		lsr
#define S2HI		lsl
#endif

/* This code is best on Thumb.  */
	.thumb

/* Parameters and result.  */
#define srcin		r0
#define result		r0

/* Internal variables.  */
#define src		r1
#define data1a		r2
#define data1b		r3
#define const_m1	r12
#define const_0		r4
#define tmp1		r4		/* Overlaps const_0  */
#define tmp2		r5

	.text
	.p2align 6
ENTRY(strlen)
	pld	[srcin, #0]
	strd	r4, r5, [sp, #-8]!
	cfi_adjust_cfa_offset (8)
	cfi_rel_offset (r4, 0)
	cfi_rel_offset (r5, 4)
	cfi_remember_state
	bic	src, srcin, #7
	mvn	const_m1, #0
	ands	tmp1, srcin, #7		/* (8 - bytes) to alignment.  */
	pld	[src, #32]
	bne.w	.Lmisaligned8
	mov	const_0, #0
	mov	result, #-8
.Lloop_aligned:
	/* Bytes 0-7.  */
	ldrd	data1a, data1b, [src]
	pld	[src, #64]
	add	result, result, #8
.Lstart_realigned:
	uadd8	data1a, data1a, const_m1	/* Saturating GE<0:3> set.  */
	sel	data1a, const_0, const_m1	/* Select based on GE<0:3>.  */
	uadd8	data1b, data1b, const_m1
	sel	data1b, data1a, const_m1	/* Only used if d1a == 0.  */
	cbnz	data1b, .Lnull_found

	/* Bytes 8-15.  */
	ldrd	data1a, data1b, [src, #8]
	uadd8	data1a, data1a, const_m1	/* Saturating GE<0:3> set.  */
	add	result, result, #8
	sel	data1a, const_0, const_m1	/* Select based on GE<0:3>.  */
	uadd8	data1b, data1b, const_m1
	sel	data1b, data1a, const_m1	/* Only used if d1a == 0.  */
	cbnz	data1b, .Lnull_found

	/* Bytes 16-23.  */
	ldrd	data1a, data1b, [src, #16]
	uadd8	data1a, data1a, const_m1	/* Saturating GE<0:3> set.  */
	add	result, result, #8
	sel	data1a, const_0, const_m1	/* Select based on GE<0:3>.  */
	uadd8	data1b, data1b, const_m1
	sel	data1b, data1a, const_m1	/* Only used if d1a == 0.  */
	cbnz	data1b, .Lnull_found

	/* Bytes 24-31.  */
	ldrd	data1a, data1b, [src, #24]
	add	src, src, #32
	uadd8	data1a, data1a, const_m1	/* Saturating GE<0:3> set.  */
	add	result, result, #8
	sel	data1a, const_0, const_m1	/* Select based on GE<0:3>.  */
	uadd8	data1b, data1b, const_m1
	sel	data1b, data1a, const_m1	/* Only used if d1a == 0.  */
	cmp	data1b, #0
	beq	.Lloop_aligned

.Lnull_found:
	cmp	data1a, #0
	itt	eq
	addeq	result, result, #4
	moveq	data1a, data1b
#ifndef __ARMEB__
	rev	data1a, data1a
#endif
	clz	data1a, data1a
	ldrd	r4, r5, [sp], #8
	cfi_adjust_cfa_offset (-8)
	cfi_restore (r4)
	cfi_restore (r5)
	add	result, result, data1a, lsr #3	/* Bits -> Bytes.  */
	DO_RET(lr)

.Lmisaligned8:
	cfi_restore_state
	ldrd	data1a, data1b, [src]
	and	tmp2, tmp1, #3
	rsb	result, tmp1, #0
	lsl	tmp2, tmp2, #3			/* Bytes -> bits.  */
	tst	tmp1, #4
	pld	[src, #64]
	S2HI	tmp2, const_m1, tmp2
	orn	data1a, data1a, tmp2
	itt	ne
	ornne	data1b, data1b, tmp2
	movne	data1a, const_m1
	mov	const_0, #0
	b	.Lstart_realigned

END(strlen)
libc_hidden_builtin_def (strlen)