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 #include "string-endian.h"
  19
  20 char *strchr(const char *s, int c)
  21 {
  22         int z, g;
  23
  24         /* Get an aligned pointer. */
  25         const uintptr_t s_int = (uintptr_t) s;
  26         const uint64_t *p = (const uint64_t *)(s_int & -8);
  27
  28         /* Create eight copies of the byte for which we are looking. */
  29         const uint64_t goal = copy_byte(c);
  30
  31         /* Read the first aligned word, but force bytes before the string to
  32          * match neither zero nor goal (we make sure the high bit of each
  33          * byte is 1, and the low 7 bits are all the opposite of the goal
  34          * byte).
  35          */
  36         const uint64_t before_mask = MASK(s_int);
  37         uint64_t v = (*p | before_mask) ^ (goal & __insn_v1shrui(before_mask, 1));
  38
  39         uint64_t zero_matches, goal_matches;
  40         while (1) {
  41                 /* Look for a terminating '\0'. */
  42                 zero_matches = __insn_v1cmpeqi(v, 0);
  43
  44                 /* Look for the goal byte. */
  45                 goal_matches = __insn_v1cmpeq(v, goal);
  46
  47                 if (__builtin_expect((zero_matches | goal_matches) != 0, 0))
  48                         break;
  49
  50                 v = *++p;
  51         }
  52
  53         z = CFZ(zero_matches);
  54         g = CFZ(goal_matches);
  55
  56         /* If we found c before '\0' we got a match. Note that if c == '\0'
  57          * then g == z, and we correctly return the address of the '\0'
  58          * rather than NULL.
  59          */
  60         return (g <= z) ? ((char *)p) + (g >> 3) : NULL;
  61 }
  62 EXPORT_SYMBOL(strchr);