string/strspn.c

   1 /* Copyright (C) 1991-2023 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <string.h>
  19 #include <stdint.h>
  20 #include <libc-pointer-arith.h>
  21
  22 #undef strspn
  23 #ifndef STRSPN
  24 # define STRSPN strspn
  25 #endif
  26
  27 /* Return the length of the maximum initial segment
  28    of S which contains only characters in ACCEPT.  */
  29 size_t
  30 STRSPN (const char *str, const char *accept)
  31 {
  32   if (accept[0] == '\0')
  33     return 0;
  34   if (__glibc_unlikely (accept[1] == '\0'))
  35     {
  36       const char *a = str;
  37       for (; *str == *accept; str++);
  38       return str - a;
  39     }
  40
  41   /* Use multiple small memsets to enable inlining on most targets.  */
  42   unsigned char table[256];
  43   unsigned char *p = memset (table, 0, 64);
  44   memset (p + 64, 0, 64);
  45   memset (p + 128, 0, 64);
  46   memset (p + 192, 0, 64);
  47
  48   unsigned char *s = (unsigned char*) accept;
  49   /* Different from strcspn it does not add the NULL on the table
  50      so can avoid check if str[i] is NULL, since table['\0'] will
  51      be 0 and thus stopping the loop check.  */
  52   do
  53     p[*s++] = 1;
  54   while (*s);
  55
  56   s = (unsigned char*) str;
  57   if (!p[s[0]]) return 0;
  58   if (!p[s[1]]) return 1;
  59   if (!p[s[2]]) return 2;
  60   if (!p[s[3]]) return 3;
  61
  62   s = (unsigned char *) PTR_ALIGN_DOWN (s, 4);
  63
  64   unsigned int c0, c1, c2, c3;
  65   do {
  66       s += 4;
  67       c0 = p[s[0]];
  68       c1 = p[s[1]];
  69       c2 = p[s[2]];
  70       c3 = p[s[3]];
  71   } while ((c0 & c1 & c2 & c3) != 0);
  72
  73   size_t count = s - (unsigned char *) str;
  74   return (c0 & c1) == 0 ? count + c0 : count + c2 + 2;
  75 }
  76 libc_hidden_builtin_def (strspn)