newlib/libc/machine/arm/strlen-stub.c

   1 /*
   2  * Copyright (c) 2008-2015 ARM Ltd
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. The name of the company may not be used to endorse or promote
  14  *    products derived from this software without specific prior written
  15  *    permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY ARM LTD ``AS IS'' AND ANY EXPRESS OR IMPLIED
  18  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
  19  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  20  * IN NO EVENT SHALL ARM LTD BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  21  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
  22  * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  23  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  24  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  25  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  26  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  */
  28
  29 #include "arm_asm.h"
  30 #include <_ansi.h>
  31 #include <string.h>
  32 #include <limits.h>
  33
  34 #if defined __OPTIMIZE_SIZE__ || defined PREFER_SIZE_OVER_SPEED
  35 #if __ARM_ARCH_ISA_THUMB == 2
  36 /* Implemented in strlen.S.  */
  37
  38 #elif defined (__ARM_ARCH_ISA_THUMB)
  39 /* Implemented in strlen.S.  */
  40
  41 #else
  42 #include "../../string/strlen.c"
  43
  44 #endif
  45
  46 #else /* defined __OPTIMIZE_SIZE__ || defined PREFER_SIZE_OVER_SPEED */
  47 #if defined __thumb__ && ! defined __thumb2__
  48 #include "../../string/strlen.c"
  49
  50 #elif __ARM_ARCH_ISA_THUMB >= 2 && defined __ARM_FEATURE_DSP
  51   /* Implemented in strlen.S.  */
  52
  53 #else
  54 size_t __attribute__((naked))
  55 strlen (const char* str)
  56 {
  57   asm ("len .req r0\n\t"
  58        "data .req r3\n\t"
  59        "addr .req r1\n\t"
  60
  61 #ifdef _ISA_ARM_7
  62        "pld [r0]\n\t"
  63 #endif
  64        /* Word-align address */
  65        "bic     addr, r0, #3\n\t"
  66        /* Get adjustment for start ... */
  67        "ands    len, r0, #3\n\t"
  68        "neg     len, len\n\t"
  69        /* First word of data */
  70        "ldr     data, [addr], #4\n\t"
  71        /* Ensure bytes preceeding start ... */
  72        "add     ip, len, #4\n\t"
  73        "mov     ip, ip, asl #3\n\t"
  74        "mvn     r2, #0\n\t"
  75        /* ... are masked out */
  76 #ifdef __thumb__
  77        "itt     ne\n\t"
  78 # ifdef __ARMEB__
  79        "lslne   r2, ip\n\t"
  80 # else
  81        "lsrne   r2, ip\n\t"
  82 # endif
  83        "orrne   data, data, r2\n\t"
  84 #else
  85        "it      ne\n\t"
  86 # ifdef __ARMEB__
  87        "orrne   data, data, r2, lsl ip\n\t"
  88 # else
  89        "orrne   data, data, r2, lsr ip\n\t"
  90 # endif
  91 #endif
  92        /* Magic const 0x01010101 */
  93 #ifdef _ISA_ARM_7
  94        "movw    ip, #0x101\n\t"
  95 #else
  96        "mov     ip, #0x1\n\t"
  97        "orr     ip, ip, ip, lsl #8\n\t"
  98 #endif
  99        "orr     ip, ip, ip, lsl #16\n"
 100
 101         /* This is the main loop.  We subtract one from each byte in
 102            the word: the sign bit changes iff the byte was zero or
 103            0x80 -- we eliminate the latter case by anding the result
 104            with the 1-s complement of the data.  */
 105        "1:\n\t"
 106        /* test (data - 0x01010101)  */
 107        "sub     r2, data, ip\n\t"
 108        /* ... & ~data */
 109        "bic     r2, r2, data\n\t"
 110        /* ... & 0x80808080 == 0? */
 111        "ands    r2, r2, ip, lsl #7\n\t"
 112 #ifdef _ISA_ARM_7
 113        /* yes, get more data... */
 114        "itt     eq\n\t"
 115        "ldreq   data, [addr], #4\n\t"
 116        /* and 4 more bytes  */
 117        "addeq   len, len, #4\n\t"
 118         /* Unroll the loop a bit.  */
 119        "pld     [addr, #8]\n\t"
 120        /*  test (data - 0x01010101)  */
 121        "ittt    eq\n\t"
 122        "subeq   r2, data, ip\n\t"
 123        /* ... & ~data */
 124        "biceq   r2, r2, data\n\t"
 125        /* ... & 0x80808080 == 0? */
 126        "andeqs  r2, r2, ip, lsl #7\n\t"
 127 #endif
 128        "itt     eq\n\t"
 129        /* yes, get more data... */
 130        "ldreq   data, [addr], #4\n\t"
 131        /* and 4 more bytes  */
 132        "addeq   len, len, #4\n\t"
 133        "beq     1b\n\t"
 134 #ifdef __ARMEB__
 135        "tst     data, #0xff000000\n\t"
 136        "itttt   ne\n\t"
 137        "addne   len, len, #1\n\t"
 138        "tstne   data, #0xff0000\n\t"
 139        "addne   len, len, #1\n\t"
 140        "tstne   data, #0xff00\n\t"
 141        "it      ne\n\t"
 142        "addne   len, len, #1\n\t"
 143 #else
 144 # ifdef _ISA_ARM_5
 145         /* R2 is the residual sign bits from the above test.  All we
 146         need to do now is establish the position of the first zero
 147         byte... */
 148         /* Little-endian is harder, we need the number of trailing
 149         zeros / 8 */
 150 #  ifdef _ISA_ARM_7
 151        "rbit    r2, r2\n\t"
 152        "clz     r2, r2\n\t"
 153 #  else
 154        "rsb     r1, r2, #0\n\t"
 155        "and     r2, r2, r1\n\t"
 156        "clz     r2, r2\n\t"
 157        "rsb     r2, r2, #31\n\t"
 158 #  endif
 159        "add     len, len, r2, lsr #3\n\t"
 160 # else  /* No CLZ instruction */
 161        "tst     data, #0xff\n\t"
 162        "itttt   ne\n\t"
 163        "addne   len, len, #1\n\t"
 164        "tstne   data, #0xff00\n\t"
 165        "addne   len, len, #1\n\t"
 166        "tstne   data, #0xff0000\n\t"
 167        "it      ne\n\t"
 168        "addne   len, len, #1\n\t"
 169 # endif
 170 #endif
 171        "bx      lr\n\t");
 172 }
 173 #endif
 174 #endif