SCM_POSFIXABLE(-1) fails with MSVC++ 6.0

[Lars J. Aas]

  Hi guys,

I've been compiling Guile 1.5.6 with MSVC++ on Cygwin.
Today I found a strange bug in my modified version, that
made this test fail:

  (if (= ( { scm_long2num(-1) } ) -1)
      (display "there is no bug\n")
      (display "there is a bug!\n"))

I tracked the problem down to SCM_POSFIXABLE(-1) failing
with MSVC++, causing scm_long2num(-1) to create a bignum
instead of an integer, but succeeding on GNU/Linux w/gcc.
I don't see immediately why it should happen - it looks
like a compiler bug to me.

Here is a fairly minimal example.  If anyone has access to
MSVC++ and can understand why it fails and how to correct
the SCM_POSFIXABLE macro to work with MSVC++, it would be
very nice, and ought to go into the Guile sources too.

  Lars J


#include <stdio.h>
#include <limits.h>

typedef signed long scm_t_signed_bits;

#ifdef CHAR_BIT
# define SCM_CHAR_BIT CHAR_BIT
#else
# define SCM_CHAR_BIT 8
#endif

#ifdef LONG_BIT
# define SCM_LONG_BIT LONG_BIT
#else
# define SCM_LONG_BIT (SCM_CHAR_BIT * sizeof (long) / sizeof (char))
#endif

#define SCM_I_FIXNUM_BIT \
  (SCM_LONG_BIT - 2)

#define SCM_MOST_POSITIVE_FIXNUM \
  ((((scm_t_signed_bits) 1) << (SCM_I_FIXNUM_BIT - 1)) - 1)

#define SCM_POSFIXABLE(n) ((n) <= SCM_MOST_POSITIVE_FIXNUM)

int
main(int argc, char ** argv)
{
  fprintf(stderr, "testing through SCM_POSFIXABLE if -1 is <= %ld - ", 
SCM_MOST_POSITIVE_FIXNUM);
  if ( SCM_POSFIXABLE(-1) ) fprintf(stderr, "true\n");
  else                      fprintf(stderr, "not so!\n");

  fprintf(stderr, "testing directly if -1 is <= %ld - ", 
SCM_MOST_POSITIVE_FIXNUM);
  if ( -1 <= 536870911 ) fprintf(stderr, "true\n");
  else                   fprintf(stderr, "not so!\n");

  return 0;
}