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annotate lib/strstr.c @ 9601:fbf94c8a908a

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Share two-way algorithm. * lib/str-two-way.h: New file, merged from... * lib/memmem.c: ...here... * lib/strstr.c: ...and here. * modules/memmem (Files): Use it. * modules/strstr (Files): Likewise. Signed-off-by: Eric Blake <ebb9@byu.net>
author Eric Blake <ebb9@byu.net>
date Thu, 10 Jan 2008 12:06:35 -0700
parents 99268e709d31
children e8d2c6fc33ad
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1 /* Copyright (C) 1991,92,93,94,96,97,98,2000,2004,2007,2008 Free Software
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2 Foundation, Inc.
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3 This file is part of the GNU C Library.
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4
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5 This program is free software; you can redistribute it and/or modify
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6 it under the terms of the GNU General Public License as published by
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7 the Free Software Foundation; either version 2, or (at your option)
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8 any later version.
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9
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10 This program is distributed in the hope that it will be useful,
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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13 GNU General Public License for more details.
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14
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15 You should have received a copy of the GNU General Public License along
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16 with this program; if not, write to the Free Software Foundation,
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17 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
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18
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19 /* This particular implementation was written by Eric Blake, 2008. */
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20
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21 #ifndef _LIBC
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22 # include <config.h>
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23 #endif
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24
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25 /* Specification of strstr. */
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26 #include <string.h>
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27
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28 #include <stdbool.h>
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29
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30 #ifndef _LIBC
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31 # define __builtin_expect(expr, val) (expr)
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32 #endif
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33
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34 #define RETURN_TYPE char *
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35 #define AVAILABLE(h, h_l, j, n_l) \
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36 (!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l)) \
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37 && ((h_l) = (j) + (n_l)))
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38 #include "str-two-way.h"
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39
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40 /* Return the first occurrence of NEEDLE in HAYSTACK. Return HAYSTACK
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41 if NEEDLE is empty, otherwise NULL if NEEDLE is not found in
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42 HAYSTACK. */
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43 char *
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44 strstr (const char *haystack_start, const char *needle_start)
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45 {
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46 const char *haystack = haystack_start;
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47 const char *needle = needle_start;
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48 size_t needle_len; /* Length of NEEDLE. */
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49 size_t haystack_len; /* Known minimum length of HAYSTACK. */
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50 bool ok = true; /* True if NEEDLE is prefix of HAYSTACK. */
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51
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52 /* Determine length of NEEDLE, and in the process, make sure
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53 HAYSTACK is at least as long (no point processing all of a long
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54 NEEDLE if HAYSTACK is too short). */
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55 while (*haystack && *needle)
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56 ok &= *haystack++ == *needle++;
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57 if (*needle)
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58 return NULL;
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59 if (ok)
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60 return (char *) haystack_start;
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61
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62 /* Reduce the size of haystack using strchr, since it has a smaller
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63 linear coefficient than the Two-Way algorithm. */
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64 needle_len = needle - needle_start;
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65 haystack = strchr (haystack_start + 1, *needle_start);
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66 if (!haystack || __builtin_expect (needle_len == 1, 0))
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67 return (char *) haystack;
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68 needle -= needle_len;
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69 haystack_len = (haystack > haystack_start + needle_len ? 1
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70 : needle_len + haystack_start - haystack);
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71
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72 /* Perform the search. Abstract memory is considered to be an array
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73 of 'unsigned char' values, not an array of 'char' values. See
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74 ISO C 99 section 6.2.6.1. */
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75 if (needle_len < LONG_NEEDLE_THRESHOLD)
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76 return two_way_short_needle ((const unsigned char *) haystack,
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77 haystack_len,
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78 (const unsigned char *) needle, needle_len);
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79 return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
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80 (const unsigned char *) needle, needle_len);
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81 }
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82
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83 #undef LONG_NEEDLE_THRESHOLD