/*
 * Copyright (c) 2008-2015 ARM Ltd
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the company may not be used to endorse or promote
 *    products derived from this software without specific prior written
 *    permission.
 *
 * THIS SOFTWARE IS PROVIDED BY ARM LTD ``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 ARM LTD BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "arm_asm.h"
#include <_ansi.h>
#include <string.h>
#include <limits.h>

#if defined __OPTIMIZE_SIZE__ || defined PREFER_SIZE_OVER_SPEED
#if __ARM_ARCH_ISA_THUMB == 2
/* Implemented in strlen.S.  */

#elif defined (__ARM_ARCH_ISA_THUMB)
/* Implemented in strlen.S.  */

#else
#include "../../string/strlen.c"

#endif

#else /* defined __OPTIMIZE_SIZE__ || defined PREFER_SIZE_OVER_SPEED */
#if defined __thumb__ && ! defined __thumb2__
#include "../../string/strlen.c"

#elif __ARM_ARCH_ISA_THUMB >= 2 && defined __ARM_FEATURE_DSP
  /* Implemented in strlen.S.  */

#else
size_t __attribute__((naked))
strlen (const char* str)
{
  asm ("len .req r0\n\t"
       "data .req r3\n\t"
       "addr .req r1\n\t"

#ifdef _ISA_ARM_7
       "pld [r0]\n\t"
#endif
       /* Word-align address */
       "bic	addr, r0, #3\n\t"
       /* Get adjustment for start ... */
       "ands	len, r0, #3\n\t"
       "neg	len, len\n\t"
       /* First word of data */
       "ldr	data, [addr], #4\n\t"
       /* Ensure bytes preceeding start ... */
       "add	ip, len, #4\n\t"
       "mov	ip, ip, asl #3\n\t"
       "mvn	r2, #0\n\t"
       /* ... are masked out */
#ifdef __thumb__
       "itt	ne\n\t"
# ifdef __ARMEB__
       "lslne	r2, ip\n\t"
# else
       "lsrne	r2, ip\n\t"
# endif
       "orrne	data, data, r2\n\t"
#else
       "it	ne\n\t"
# ifdef __ARMEB__
       "orrne	data, data, r2, lsl ip\n\t"
# else
       "orrne	data, data, r2, lsr ip\n\t"
# endif
#endif
       /* Magic const 0x01010101 */
#ifdef _ISA_ARM_7
       "movw	ip, #0x101\n\t"
#else
       "mov	ip, #0x1\n\t"
       "orr	ip, ip, ip, lsl #8\n\t"
#endif
       "orr	ip, ip, ip, lsl #16\n"

	/* This is the main loop.  We subtract one from each byte in
	   the word: the sign bit changes iff the byte was zero or
	   0x80 -- we eliminate the latter case by anding the result
	   with the 1-s complement of the data.  */
       "1:\n\t"
       /* test (data - 0x01010101)  */
       "sub	r2, data, ip\n\t"
       /* ... & ~data */
       "bic	r2, r2, data\n\t"
       /* ... & 0x80808080 == 0? */
       "ands	r2, r2, ip, lsl #7\n\t"
#ifdef _ISA_ARM_7
       /* yes, get more data... */
       "itt	eq\n\t"
       "ldreq	data, [addr], #4\n\t"
       /* and 4 more bytes  */
       "addeq	len, len, #4\n\t"
	/* Unroll the loop a bit.  */
       "pld	[addr, #8]\n\t"
       /*  test (data - 0x01010101)  */
       "ittt	eq\n\t"
       "subeq	r2, data, ip\n\t"
       /* ... & ~data */
       "biceq	r2, r2, data\n\t"
       /* ... & 0x80808080 == 0? */
       "andeqs	r2, r2, ip, lsl #7\n\t"
#endif
       "itt	eq\n\t"
       /* yes, get more data... */
       "ldreq	data, [addr], #4\n\t"
       /* and 4 more bytes  */
       "addeq	len, len, #4\n\t"
       "beq	1b\n\t"
#ifdef __ARMEB__
       "tst	data, #0xff000000\n\t"
       "itttt	ne\n\t"
       "addne	len, len, #1\n\t"
       "tstne	data, #0xff0000\n\t"
       "addne	len, len, #1\n\t"
       "tstne	data, #0xff00\n\t"
       "it	ne\n\t"
       "addne	len, len, #1\n\t"
#else
# ifdef _ISA_ARM_5
	/* R2 is the residual sign bits from the above test.  All we
	need to do now is establish the position of the first zero
	byte... */
	/* Little-endian is harder, we need the number of trailing
	zeros / 8 */
#  ifdef _ISA_ARM_7
       "rbit	r2, r2\n\t"
       "clz	r2, r2\n\t"
#  else
       "rsb	r1, r2, #0\n\t"
       "and	r2, r2, r1\n\t"
       "clz	r2, r2\n\t"
       "rsb	r2, r2, #31\n\t"
#  endif
       "add	len, len, r2, lsr #3\n\t"
# else  /* No CLZ instruction */
       "tst	data, #0xff\n\t"
       "itttt	ne\n\t"
       "addne	len, len, #1\n\t"
       "tstne	data, #0xff00\n\t"
       "addne	len, len, #1\n\t"
       "tstne	data, #0xff0000\n\t"
       "it	ne\n\t"
       "addne	len, len, #1\n\t"
# endif
#endif
       "bx	lr\n\t");
}
#endif
#endif