gdb/gnulib/m4/memmem.m4

   1 # memmem.m4 serial 9
   2 dnl Copyright (C) 2002, 2003, 2004, 2007, 2008 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.
   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_REPLACE_FUNCS(memmem)
  15   AC_CHECK_DECLS_ONCE(memmem)
  16   if test $ac_cv_have_decl_memmem = no; then
  17     HAVE_DECL_MEMMEM=0
  18   fi
  19   gl_PREREQ_MEMMEM
  20 ]) # gl_FUNC_MEMMEM_SIMPLE
  21
  22 dnl Additionally, check that memmem is efficient and handles empty needles.
  23 AC_DEFUN([gl_FUNC_MEMMEM],
  24 [
  25   AC_REQUIRE([gl_FUNC_MEMMEM_SIMPLE])
  26   if test $ac_cv_have_decl_memmem = yes; then
  27     AC_CACHE_CHECK([whether memmem works in linear time],
  28       [gl_cv_func_memmem_works],
  29       [AC_RUN_IFELSE([AC_LANG_PROGRAM([
  30 #include <string.h> /* for memmem */
  31 #include <stdlib.h> /* for malloc */
  32 #include <unistd.h> /* for alarm */
  33 ], [[size_t m = 1000000;
  34     char *haystack = (char *) malloc (2 * m + 1);
  35     char *needle = (char *) malloc (m + 1);
  36     void *result = 0;
  37     /* Failure to compile this test due to missing alarm is okay,
  38        since all such platforms (mingw) also lack memmem.  */
  39     alarm (5);
  40     /* Check for quadratic performance.  */
  41     if (haystack && needle)
  42       {
  43         memset (haystack, 'A', 2 * m);
  44         haystack[2 * m] = 'B';
  45         memset (needle, 'A', m);
  46         needle[m] = 'B';
  47         result = memmem (haystack, 2 * m + 1, needle, m + 1);
  48       }
  49     /* Check for empty needle behavior.  */
  50     return !result || !memmem ("a", 1, 0, 0);]])],
  51         [gl_cv_func_memmem_works=yes], [gl_cv_func_memmem_works=no],
  52         [dnl pessimistically assume the worst, since even glibc 2.6.1
  53          dnl has quadratic complexity in its memmem
  54          gl_cv_func_memmem_works="guessing no"])])
  55     if test "$gl_cv_func_memmem_works" != yes; then
  56       REPLACE_MEMMEM=1
  57       AC_LIBOBJ([memmem])
  58     fi
  59   fi
  60 ]) # gl_FUNC_MEMMEM
  61
  62 # Prerequisites of lib/memmem.c.
  63 AC_DEFUN([gl_PREREQ_MEMMEM], [:])