gnulib/import/m4/memmem.m4

   1 # memmem.m4 serial 26
   2 dnl Copyright (C) 2002-2004, 2007-2019 Free Software Foundation, Inc.
   3 dnl This file is free software; the Free Software Foundation
   4 dnl gives unlimited permission to copy and/or distribute it,
   5 dnl with or without modifications, as long as this notice is preserved.
   6
   7 dnl Check that memmem is present and functional.
   8 AC_DEFUN([gl_FUNC_MEMMEM_SIMPLE],
   9 [
  10   dnl Persuade glibc <string.h> to declare memmem().
  11   AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS])
  12
  13   AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS])
  14   AC_CHECK_FUNCS([memmem])
  15   if test $ac_cv_func_memmem = yes; then
  16     HAVE_MEMMEM=1
  17   else
  18     HAVE_MEMMEM=0
  19   fi
  20   AC_CHECK_DECLS_ONCE([memmem])
  21   if test $ac_cv_have_decl_memmem = no; then
  22     HAVE_DECL_MEMMEM=0
  23   else
  24     dnl Detect https://sourceware.org/bugzilla/show_bug.cgi?id=12092.
  25     dnl Also check that we handle empty needles correctly.
  26     AC_CACHE_CHECK([whether memmem works],
  27       [gl_cv_func_memmem_works_always],
  28       [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
  29 #include <string.h> /* for memmem */
  30 #define P "_EF_BF_BD"
  31 #define HAYSTACK "F_BD_CE_BD" P P P P "_C3_88_20" P P P "_C3_A7_20" P
  32 #define NEEDLE P P P P P
  33 ]], [[
  34     int result = 0;
  35     if (memmem (HAYSTACK, strlen (HAYSTACK), NEEDLE, strlen (NEEDLE)))
  36       result |= 1;
  37     /* Check for empty needle behavior.  */
  38     {
  39       const char *haystack = "AAA";
  40       if (memmem (haystack, 3, NULL, 0) != haystack)
  41         result |= 2;
  42     }
  43     return result;
  44     ]])],
  45         [gl_cv_func_memmem_works_always=yes],
  46         [gl_cv_func_memmem_works_always=no],
  47         [dnl glibc 2.9..2.12 and cygwin 1.7.7 have issue #12092 above.
  48          dnl Also empty needles work on glibc >= 2.1 and cygwin >= 1.7.0.
  49          dnl uClibc is not affected, since it uses different source code.
  50          dnl Assume that it works on all other platforms (even if not linear).
  51          AC_EGREP_CPP([Lucky user],
  52            [
  53 #ifdef __GNU_LIBRARY__
  54  #include <features.h>
  55  #if ((__GLIBC__ == 2 && ((__GLIBC_MINOR > 0 && __GLIBC_MINOR__ < 9) \
  56                           || __GLIBC_MINOR__ > 12)) \
  57       || (__GLIBC__ > 2)) \
  58      || defined __UCLIBC__
  59   Lucky user
  60  #endif
  61 #elif defined __CYGWIN__
  62  #include <cygwin/version.h>
  63  #if CYGWIN_VERSION_DLL_COMBINED > CYGWIN_VERSION_DLL_MAKE_COMBINED (1007, 7)
  64   Lucky user
  65  #endif
  66 #else
  67   Lucky user
  68 #endif
  69            ],
  70            [gl_cv_func_memmem_works_always="guessing yes"],
  71            [gl_cv_func_memmem_works_always="$gl_cross_guess_normal"])
  72         ])
  73       ])
  74     case "$gl_cv_func_memmem_works_always" in
  75       *yes) ;;
  76       *)
  77         REPLACE_MEMMEM=1
  78         ;;
  79     esac
  80   fi
  81   gl_PREREQ_MEMMEM
  82 ]) # gl_FUNC_MEMMEM_SIMPLE
  83
  84 dnl Additionally, check that memmem has linear performance characteristics
  85 AC_DEFUN([gl_FUNC_MEMMEM],
  86 [
  87   AC_REQUIRE([gl_FUNC_MEMMEM_SIMPLE])
  88   if test $HAVE_DECL_MEMMEM = 1 && test $REPLACE_MEMMEM = 0; then
  89     AC_CACHE_CHECK([whether memmem works in linear time],
  90       [gl_cv_func_memmem_works_fast],
  91       [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
  92 #include <signal.h> /* for signal */
  93 #include <string.h> /* for memmem */
  94 #include <stdlib.h> /* for malloc */
  95 #include <unistd.h> /* for alarm */
  96 static void quit (int sig) { _exit (sig + 128); }
  97 ]], [[
  98     int result = 0;
  99     size_t m = 1000000;
 100     char *haystack = (char *) malloc (2 * m + 1);
 101     char *needle = (char *) malloc (m + 1);
 102     /* Failure to compile this test due to missing alarm is okay,
 103        since all such platforms (mingw) also lack memmem.  */
 104     signal (SIGALRM, quit);
 105     alarm (5);
 106     /* Check for quadratic performance.  */
 107     if (haystack && needle)
 108       {
 109         memset (haystack, 'A', 2 * m);
 110         haystack[2 * m] = 'B';
 111         memset (needle, 'A', m);
 112         needle[m] = 'B';
 113         if (!memmem (haystack, 2 * m + 1, needle, m + 1))
 114           result |= 1;
 115       }
 116     /* Free allocated memory, in case some sanitizer is watching.  */
 117     free (haystack);
 118     free (needle);
 119     return result;
 120     ]])],
 121         [gl_cv_func_memmem_works_fast=yes], [gl_cv_func_memmem_works_fast=no],
 122         [dnl Only glibc >= 2.9 and cygwin > 1.7.0 are known to have a
 123          dnl memmem that works in linear time.
 124          AC_EGREP_CPP([Lucky user],
 125            [
 126 #include <features.h>
 127 #ifdef __GNU_LIBRARY__
 128  #if ((__GLIBC__ == 2 && __GLIBC_MINOR__ >= 9) || (__GLIBC__ > 2)) \
 129      && !defined __UCLIBC__
 130   Lucky user
 131  #endif
 132 #endif
 133 #ifdef __CYGWIN__
 134  #include <cygwin/version.h>
 135  #if CYGWIN_VERSION_DLL_COMBINED > CYGWIN_VERSION_DLL_MAKE_COMBINED (1007, 0)
 136   Lucky user
 137  #endif
 138 #endif
 139            ],
 140            [gl_cv_func_memmem_works_fast="guessing yes"],
 141            [gl_cv_func_memmem_works_fast="$gl_cross_guess_normal"])
 142         ])
 143       ])
 144     case "$gl_cv_func_memmem_works_fast" in
 145       *yes) ;;
 146       *)
 147         REPLACE_MEMMEM=1
 148         ;;
 149     esac
 150   fi
 151 ]) # gl_FUNC_MEMMEM
 152
 153 # Prerequisites of lib/memmem.c.
 154 AC_DEFUN([gl_PREREQ_MEMMEM], [:])