c99-backport.m4

# AC_PROG_CC_C99 ([ACTION-IF-AVAILABLE], [ACTION-IF-UNAVAILABLE])
# ----------------------------------------------------------------
# If the C compiler is not in ISO C99 mode by default, try to add an
# option to output variable CC to make it so.  This macro tries
# various options that select ISO C99 on some system or another.  It
# considers the compiler to be in ISO C99 mode if it handles _Bool,
# // comments, flexible array members, inline, long long int, mixed
# code and declarations, named initialization of structs, restrict,
# va_copy, varargs macros, variable declarations in for loops and
# variable length arrays.
AC_DEFUN([AC_PROG_CC_C99],
[AC_C_STD_TRY([c99],
[[#include <stdarg.h>
#include <stdbool.h>
#include <stdlib.h>
#include <wchar.h>
#include <stdio.h>

// Check varargs macros.  These examples are taken from C99 6.10.3.5.
#define debug(...) fprintf (stderr, __VA_ARGS__)
#define showlist(...) puts (#__VA_ARGS__)
#define report(test,...) ((test) ? puts (#test) : printf (__VA_ARGS__))
static void
test_varargs_macros (void)
{
  int x = 1234;
  int y = 5678;
  debug ("Flag");
  debug ("X = %d\n", x);
  showlist (The first, second, and third items.);
  report (x>y, "x is %d but y is %d", x, y);
}

// Check long long types.
#define BIG64 18446744073709551615ull
#define BIG32 4294967295ul
#define BIG_OK (BIG64 / BIG32 == 4294967297ull && BIG64 % BIG32 == 0)
#if !BIG_OK
  your preprocessor is broken;
#endif
#if BIG_OK
#else
  your preprocessor is broken;
#endif
static long long int bignum = -9223372036854775807LL;
static unsigned long long int ubignum = BIG64;

struct incomplete_array
{
  int datasize;
  double data[];
};

struct named_init {
  int number;
  const wchar_t *name;
  double average;
};

typedef const char *ccp;

static inline int
test_restrict (ccp restrict text)
{
  // See if C++-style comments work.
  // Iterate through items via the restricted pointer.
  // Also check for declarations in for loops.
  for (unsigned int i = 0; *(text+i) != '\0'; ++i)
    continue;
  return 0;
}

// Check varargs and va_copy.
static void
test_varargs (const char *format, ...)
{
  va_list args;
  va_start (args, format);
  va_list args_copy;
  va_copy (args_copy, args);

  const char *str;
  int number;
  float fnumber;

  while (*format)
    {
      switch (*format++)
	{
	case 's': // string
	  str = va_arg (args_copy, const char *);
	  break;
	case 'd': // int
	  number = va_arg (args_copy, int);
	  break;
	case 'f': // float
	  fnumber = va_arg (args_copy, double);
	  break;
	default:
	  break;
	}
    }
  va_end (args_copy);
  va_end (args);
}
]],
[[
  // Check bool.
  _Bool success = false;

  // Check restrict.
  if (test_restrict ("String literal") == 0)
    success = true;
  char *restrict newvar = "Another string";

  // Check varargs.
  test_varargs ("s, d' f .", "string", 65, 34.234);
  test_varargs_macros ();

  // Check flexible array members.
  struct incomplete_array *ia =
    malloc (sizeof (struct incomplete_array) + (sizeof (double) * 10));
  ia->datasize = 10;
  for (int i = 0; i < ia->datasize; ++i)
    ia->data[i] = i * 1.234;

  // Check named initializers.
  struct named_init ni = {
    .number = 34,
    .name = L"Test wide string",
    .average = 543.34343,
  };

  ni.number = 58;

  int dynamic_array[ni.number];
  dynamic_array[ni.number - 1] = 543;

  // work around unused variable warnings
  return (!success || bignum == 0LL || ubignum == 0uLL || newvar[0] == 'x'
	  || dynamic_array[ni.number - 1] != 543);
]],
dnl Try
dnl GCC		-std=gnu99 (unused restrictive modes: -std=c99 -std=iso9899:1999)
dnl AIX		-qlanglvl=extc99 (unused restrictive mode: -qlanglvl=stdc99)
dnl Intel ICC	-c99
dnl IRIX	-c99
dnl Solaris	(unused because it causes the compiler to assume C99 semantics for
dnl		library functions, and this is invalid before Solaris 10: -xc99)
dnl Tru64	-c99
dnl with extended modes being tried first.
[[-std=gnu99 -c99 -qlanglvl=extc99]], [$1], [$2])[]dnl
])# AC_PROG_CC_C99

# AC_C_STD_TRY(STANDARD, TEST-PROLOGUE, TEST-BODY, OPTION-LIST,
#		ACTION-IF-AVAILABLE, ACTION-IF-UNAVAILABLE)
# --------------------------------------------------------------
# Check whether the C compiler accepts features of STANDARD (e.g `c89', `c99')
# by trying to compile a program of TEST-PROLOGUE and TEST-BODY.  If this fails,
# try again with each compiler option in the space-separated OPTION-LIST; if one
# helps, append it to CC.  If eventually successful, run ACTION-IF-AVAILABLE,
# else ACTION-IF-UNAVAILABLE.
AC_DEFUN([AC_C_STD_TRY],
[AC_MSG_CHECKING([for $CC option to accept ISO ]m4_translit($1, [c], [C]))
AC_CACHE_VAL(ac_cv_prog_cc_$1,
[ac_cv_prog_cc_$1=no
ac_save_CC=$CC
AC_LANG_CONFTEST([AC_LANG_PROGRAM([$2], [$3])])
for ac_arg in '' $4
do
  CC="$ac_save_CC $ac_arg"
  _AC_COMPILE_IFELSE([], [ac_cv_prog_cc_$1=$ac_arg])
  test "x$ac_cv_prog_cc_$1" != "xno" && break
done
rm -f conftest.$ac_ext
CC=$ac_save_CC
])# AC_CACHE_VAL
case "x$ac_cv_prog_cc_$1" in
  x)
    AC_MSG_RESULT([none needed]) ;;
  xno)
    AC_MSG_RESULT([unsupported]) ;;
  *)
    CC="$CC $ac_cv_prog_cc_$1"
    AC_MSG_RESULT([$ac_cv_prog_cc_$1]) ;;
esac
AS_IF([test "x$ac_cv_prog_cc_$1" != xno], [$5], [$6])
])# AC_C_STD_TRY