dnl @synopsis AC_COMPILE_CHECK_SIZEOF(TYPE [, HEADERS [, EXTRA_SIZES...]])
dnl
dnl This macro checks for the size of TYPE using compile checks, not
dnl run checks. You can supply extra HEADERS to look into. the check
dnl will cycle through 1 2 4 8 16 and any EXTRA_SIZES the user
dnl supplies. If a match is found, it will #define SIZEOF_`TYPE' to
dnl that value. Otherwise it will emit a configure time error
dnl indicating the size of the type could not be determined.
dnl
dnl The trick is that C will not allow duplicate case labels. While
dnl this is valid C code:
dnl
dnl      switch (0) case 0: case 1:;
dnl
dnl The following is not:
dnl
dnl      switch (0) case 0: case 0:;
dnl
dnl Thus, the AC_TRY_COMPILE will fail if the currently tried size
dnl does not match.
dnl
dnl Here is an example skeleton configure.in script, demonstrating the
dnl macro's usage:
dnl
dnl      AC_PROG_CC
dnl      AC_CHECK_HEADERS(stddef.h unistd.h)
dnl      AC_TYPE_SIZE_T
dnl      AC_CHECK_TYPE(ssize_t, int)
dnl
dnl      headers='#ifdef HAVE_STDDEF_H
dnl      #include <stddef.h>
dnl      #endif
dnl      #ifdef HAVE_UNISTD_H
dnl      #include <unistd.h>
dnl      #endif
dnl      '
dnl
dnl      AC_COMPILE_CHECK_SIZEOF(char)
dnl      AC_COMPILE_CHECK_SIZEOF(short)
dnl      AC_COMPILE_CHECK_SIZEOF(int)
dnl      AC_COMPILE_CHECK_SIZEOF(long)
dnl      AC_COMPILE_CHECK_SIZEOF(unsigned char *)
dnl      AC_COMPILE_CHECK_SIZEOF(void *)
dnl      AC_COMPILE_CHECK_SIZEOF(size_t, $headers)
dnl      AC_COMPILE_CHECK_SIZEOF(ssize_t, $headers)
dnl      AC_COMPILE_CHECK_SIZEOF(ptrdiff_t, $headers)
dnl      AC_COMPILE_CHECK_SIZEOF(off_t, $headers)
dnl
dnl @author Kaveh Ghazi <ghazi@caip.rutgers.edu>
dnl @version $Id: ac_compile_check_sizeof.m4,v 1.1.1.1 2001/07/26 00:46 ac-archive-0.5.39 $
dnl
AC_DEFUN([AC_COMPILE_CHECK_SIZEOF],
[changequote(<<, >>)dnl
dnl The name to #define.
define(<<AC_TYPE_NAME>>, translit(sizeof_$1, [a-z *], [A-Z_P]))dnl
dnl The cache variable name.
define(<<AC_CV_NAME>>, translit(ac_cv_sizeof_$1, [ *], [_p]))dnl
changequote([, ])dnl
AC_MSG_CHECKING(size of $1)
AC_CACHE_VAL(AC_CV_NAME,
[for ac_size in 4 8 1 2 16 $2 ; do # List sizes in rough order of prevalence.
  AC_TRY_COMPILE([#include "confdefs.h"
#include <sys/types.h>
$2
], [switch (0) case 0: case (sizeof ($1) == $ac_size):;], AC_CV_NAME=$ac_size)
  if test x$AC_CV_NAME != x ; then break; fi
done
])
if test x$AC_CV_NAME = x ; then
  AC_MSG_ERROR([cannot determine a size for $1])
fi
AC_MSG_RESULT($AC_CV_NAME)
AC_DEFINE_UNQUOTED(AC_TYPE_NAME, $AC_CV_NAME, [The number of bytes in type $1])
undefine([AC_TYPE_NAME])dnl
undefine([AC_CV_NAME])dnl
])
