Bug #22285: FIX2INT loses consistency due to sizeof(int)

• Status: Open
• Assignee: -
• Target version: -
• Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN

[YO4 (Yoshinao Muramatsu)]

In include/ruby/internal/arithmetic/int.h, FIX2INT is resolved to rb_fix2int or RB_FIX2LONG.

#define FIX2INT    RB_FIX2INT          /**< @old{RB_FIX2INT} */

/**
 * Converts a Fixnum into C's `int`.
 *
 * @param[in]  x  Some Fixnum.
 * @pre        Must not pass anything other than a Fixnum.
 * @return     The passed value converted into C's `int`.
 */
static inline int
RB_FIX2INT(VALUE x)
{
    /* “FIX2INT raises a `TypeError` if passed `nil`,” says rubyspec.  Not sure if
     * that is the intended behavior, but just preserving backward compatibility.
     */
#if 0
    RBIMPL_ASSERT_OR_ASSUME(RB_FIXNUM_P(x));
#endif
    long ret;

    if /* constexpr */ (sizeof(int) < sizeof(long)) {
        ret = rb_fix2int(x);
    }
    else {
        ret = RB_FIX2LONG(x);
    }

    return RBIMPL_CAST((int)ret);
}

RB_FIX2LONG takes a fast path using shift operations, whereas rb_fix2int performs a more complex process by calling rb_num2long based on the result of the FIXNUM_P check.

This goes beyond the scope of rdoc and doc/extensions.
Is it intended behavior for FIX2INT to call to_int?
Since the FIXNUM_P guard has become an idiom, this seems like unnecessary behavior.

Note that there is a possibility that an implementer could unintentionally create code that breaks under Windows and probably 32-bit platforms,
(see Bug #22284)