macro FIXNUM_OVERFLOW_P in lisp.h is valid ?

[Toru TSUNEYOSHI]

Hello.

I read the code of function `string-to-number', and traced functions or
macros recursively.

  traces of string-to-number:

    data.c: Fstring_to_number
      lisp.h: make_fixnum_or_float
        lisp.h: FIXNUM_OVERFLOW_P

  citation of FIXNUM_OVERFLOW_P (in Emacs 23.1):

    /* Value is non-zero if C integer I doesn't fit into a Lisp fixnum.  */

    #define FIXNUM_OVERFLOW_P(i) \
      ((EMACS_INT)(i) > MOST_POSITIVE_FIXNUM \
       || (EMACS_INT) (i) < MOST_NEGATIVE_FIXNUM)

I think FIXNUM_OVERFLOW_P is problematic.

The reason is that
in case `i' is 4294967296.0 (2^32), (EMACS_INT)(i) returns 0
with a executable program by some compiler
(for example, Microsoft 32-bit C/C++ Compiler).
As a result, FIXNUM_OVERFLOW_P(i) returns 0.

  In Microsoft 32-bit C/C++ Compiler:

    i                                   (int)(i)
    ===============================================
    2147483648.0        (2^31)          -2147483648
    2147483647.0        (2^31 - 1)       2147483647

    4294967296.0        (2^32)           0
    4294967295.0        (2^32 - 1)      -1

    8589934592.0        (2^33)           0
    8589934591.0        (2^33 - 1)       -1

  In gcc version 3.4.4 (cygming special):

    i                                   (int)(i)
    ===============================================
    2147483648.0        (2^31)          -2147483648
    2147483647.0        (2^31 - 1)       2147483647

    4294967296.0        (2^32)          -2147483648
    4294967295.0        (2^32 - 1)      -2147483648

    8589934592.0        (2^33)          -2147483648
    8589934591.0        (2^33 - 1)      -2147483648

In conclusion, it needs casting to double, I think.

    #define FIXNUM_OVERFLOW_P(i) \
      ((double)(i) > (double)MOST_POSITIVE_FIXNUM \
       || (double)(i) < (double)MOST_NEGATIVE_FIXNUM)

What do you think about it ?