Re: exact-width C Integers and Autoconf

[Paul Eggert]

> From: "Simon Waters" <address@hidden>
> Date: Thu, 21 Feb 2002 02:31:30 -0000

> I need to define 32 and 64 bit integer types in reasonably portable C.

I assume you mean exact-width 32 and 64 bit types.  The C standard
does not require the existence of such types; for example, you might
be on a 36-bit host that has 36-bit int and 72-bit long.  However,
such machines are admittedly rare these days.

> Linux can include "inttypes.h" these days, so I'm happy to rename to the =
> "standard" names.

Yes, that's the better way in the long run.  The standard names will
take over eventually.

> Is there an autoconf example to follow?=20

Not that I know of.  I would put this into configure.ac:

AC_CHECK_HEADERS(inttypes.h limits.h stdint.h)

and put something like the following into my C code:

  #include <config.h>

  #if HAVE_LIMITS_H
  # include <limits.h>
  #endif

  #if HAVE_INTTYPES_H
  # include <inttypes.h>
  #else
  # if HAVE_STDINT_H
  #  include <stdint.h>
  # endif
  #endif

  #ifndef INT32_MAX 
  # if INT_MAX == 2147483647
  #  define int32_t int
  #  define INT32_MAX 2147483647
  # else
  #  if LONG_MAX == 2147483647
  #   define int32_t long
  #   define INT32_MAX 2147483647L
  #  else
      This code assumes the existence of 32-bit exact-width
      integers, and will not work on machines that lack such a type.
  #  endif
  # endif
  #endif

  /* Avoids integer overflow on 32-bit hosts.  */
  # define EQUALS_INT64_MAX(x) \
      ((x) / 65536 / 65536 == 2147483647 && (x) % 2147483647 == 1)

  #ifndef INT64_MAX
  # if EQUALS_INT64_MAX (INT_MAX)
  #  define int64_t int
  #  define INT64_MAX 9223372036854775807
  # else
  #  if EQUALS_INT64_MAX (LONG_MAX)
  #   define int64_t long
  #   define INT64_MAX 9223372036854775807L
  #  else
  #   if EQUALS_INT64_MAX (LLONG_MAX)
  #    define int64_t long long
  #    define INT64_MAX 9223372036854775807LL
  #   else
       This code assumes the existence of 64-bit exact-width
       integers, and will not work on machines that lack such a type.
  #   endif
  #  endif
  # endif
  #endif

Admittedly EQUALS_INT64_MAX is a bit tricky.  Perhaps something like
this should be turned into an autoconf macro, though we probably need
more experience.  I'll CC this message to address@hidden to see if
there are other opinions.

> This is a multi-part message in MIME format.

Please send text mail as plaintext; it saves me time.  Thanks.