/*
 * Copyright (c) 2008 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) || \
  (defined (__thumb__) && !defined (__thumb2__))

# if !defined (PREFER_SIZE_OVER_SPEED) && !defined (__OPTIMIZE_SIZE__)
/* Thumb1 only variant.
   If speed is preferred, the strlen() function in ../../string/strlen.c
   will be used.

   Leave this field blank.  So the strlen() is not defined, and this will
   automatically pull in the default C definition of strlen() from
   ../../string/strlen.c.  No need to include this file explicitely.
   The lib_a-strlen.o will not be generated, so it won't replace the default
   lib_a-strlen.o which is generated by ../../string/strlen.c.  See the
   commands in configure.in and Makefile.am for more details.

   However, if we need to rewrite this function to be more efficient,
   we can add the corresponding assembly code into this field and change
   the commands in configure.in and Makefile.am to allow the corresponding
   lib_a-strlen.o to be generated.
*/
# else
size_t
strlen (const char* str)
{
  int scratch;
#if defined (__thumb__) && !defined (__thumb2__)
  size_t len;
  asm ("mov	%0, #0\n"
       "1:\n\t"
       "ldrb	%1, [%2, %0]\n\t"
       "add	%0, %0, #1\n\t"
       "cmp	%1, #0\n\t"
       "bne	1b"
       : "=&r" (len), "=&r" (scratch) : "r" (str) : "memory", "cc");
  return len - 1;
#else
  const char* end;
  asm ("1:\n\t"
       "ldrb	%1, [%0], #1\n\t"
       "cmp	%1, #0\n\t"
       "bne	1b"
       : "=&r" (end), "=&r" (scratch) : "0" (str) : "memory", "cc");
  return end - str - 1;
#endif
}
#endif
#else

#if !(defined(_ISA_ARM_7) || defined(__ARM_ARCH_6T2__))

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

       "optpld r0\n\t"
       /* 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"
	/* If we have PLD, then unroll the loop a bit.  */
       "optpld 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
       "RETURN");
}
#endif
#endif