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annotate lib/strstr.c @ 17616:cae23a655793

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author Karl Berry <karl@freefriends.org>
date Sat, 25 Jan 2014 06:40:43 -0800
parents 344018b6e5d7
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1 /* Copyright (C) 1991-1994, 1996-1998, 2000, 2004, 2007-2014 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, see <http://www.gnu.org/licenses/>. */
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17
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18 /* This particular implementation was written by Eric Blake, 2008. */
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19
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20 #ifndef _LIBC
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21 # include <config.h>
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22 #endif
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23
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24 /* Specification of strstr. */
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25 #include <string.h>
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26
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27 #include <stdbool.h>
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28
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29 #ifndef _LIBC
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30 # define __builtin_expect(expr, val) (expr)
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31 #endif
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32
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33 #define RETURN_TYPE char *
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34 #define AVAILABLE(h, h_l, j, n_l) \
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35 (!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l)) \
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36 && ((h_l) = (j) + (n_l)))
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37 #include "str-two-way.h"
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38
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39 /* Return the first occurrence of NEEDLE in HAYSTACK. Return HAYSTACK
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40 if NEEDLE is empty, otherwise NULL if NEEDLE is not found in
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41 HAYSTACK. */
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42 char *
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43 strstr (const char *haystack_start, const char *needle_start)
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44 {
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45 const char *haystack = haystack_start;
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46 const char *needle = needle_start;
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47 size_t needle_len; /* Length of NEEDLE. */
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48 size_t haystack_len; /* Known minimum length of HAYSTACK. */
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49 bool ok = true; /* True if NEEDLE is prefix of HAYSTACK. */
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50
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51 /* Determine length of NEEDLE, and in the process, make sure
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52 HAYSTACK is at least as long (no point processing all of a long
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53 NEEDLE if HAYSTACK is too short). */
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54 while (*haystack && *needle)
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55 ok &= *haystack++ == *needle++;
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56 if (*needle)
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57 return NULL;
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58 if (ok)
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59 return (char *) haystack_start;
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60
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61 /* Reduce the size of haystack using strchr, since it has a smaller
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62 linear coefficient than the Two-Way algorithm. */
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63 needle_len = needle - needle_start;
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64 haystack = strchr (haystack_start + 1, *needle_start);
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65 if (!haystack || __builtin_expect (needle_len == 1, 0))
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66 return (char *) haystack;
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67 needle -= needle_len;
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68 haystack_len = (haystack > haystack_start + needle_len ? 1
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69 : needle_len + haystack_start - haystack);
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70
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71 /* Perform the search. Abstract memory is considered to be an array
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72 of 'unsigned char' values, not an array of 'char' values. See
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73 ISO C 99 section 6.2.6.1. */
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74 if (needle_len < LONG_NEEDLE_THRESHOLD)
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75 return two_way_short_needle ((const unsigned char *) haystack,
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76 haystack_len,
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77 (const unsigned char *) needle, needle_len);
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78 return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
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79 (const unsigned char *) needle, needle_len);
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80 }
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81
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82 #undef LONG_NEEDLE_THRESHOLD