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/*

 * 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__))

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

}

#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"

       "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