arch/tile/lib/strchr_64.c

   1 /*
   2  * Copyright 2011 Tilera Corporation. All Rights Reserved.
   3  *
   4  *   This program is free software; you can redistribute it and/or
   5  *   modify it under the terms of the GNU General Public License
   6  *   as published by the Free Software Foundation, version 2.
   7  *
   8  *   This program is distributed in the hope that it will be useful, but
   9  *   WITHOUT ANY WARRANTY; without even the implied warranty of
  10  *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
  11  *   NON INFRINGEMENT.  See the GNU General Public License for
  12  *   more details.
  13  */
  14
  15 #include <linux/types.h>
  16 #include <linux/string.h>
  17 #include <linux/module.h>
  18
  19 #undef strchr
  20
  21 char *strchr(const char *s, int c)
  22 {
  23         int z, g;
  24
  25         /* Get an aligned pointer. */
  26         const uintptr_t s_int = (uintptr_t) s;
  27         const uint64_t *p = (const uint64_t *)(s_int & -8);
  28
  29         /* Create eight copies of the byte for which we are looking. */
  30         const uint64_t goal = 0x0101010101010101ULL * (uint8_t) c;
  31
  32         /* Read the first aligned word, but force bytes before the string to
  33          * match neither zero nor goal (we make sure the high bit of each
  34          * byte is 1, and the low 7 bits are all the opposite of the goal
  35          * byte).
  36          *
  37          * Note that this shift count expression works because we know shift
  38          * counts are taken mod 64.
  39          */
  40         const uint64_t before_mask = (1ULL << (s_int << 3)) - 1;
  41         uint64_t v = (*p | before_mask) ^
  42                 (goal & __insn_v1shrsi(before_mask, 1));
  43
  44         uint64_t zero_matches, goal_matches;
  45         while (1) {
  46                 /* Look for a terminating '\0'. */
  47                 zero_matches = __insn_v1cmpeqi(v, 0);
  48
  49                 /* Look for the goal byte. */
  50                 goal_matches = __insn_v1cmpeq(v, goal);
  51
  52                 if (__builtin_expect((zero_matches | goal_matches) != 0, 0))
  53                         break;
  54
  55                 v = *++p;
  56         }
  57
  58         z = __insn_ctz(zero_matches);
  59         g = __insn_ctz(goal_matches);
  60
  61         /* If we found c before '\0' we got a match. Note that if c == '\0'
  62          * then g == z, and we correctly return the address of the '\0'
  63          * rather than NULL.
  64          */
  65         return (g <= z) ? ((char *)p) + (g >> 3) : NULL;
  66 }
  67 EXPORT_SYMBOL(strchr);