[Numpy-discussion] RE: Python 2.2 seriously crippled for numerical computation?

[Skip Montanaro]

    Fernando> It's not Python 2.2 itself:

    Fernando> % python
    Fernando> Python 2.2 (#1, Feb 10 2002, 13:29:43)
    Fernando> [GCC 2.95.2 19991024 (release)] on darwin
    Fernando> Type "help", "copyright", "credits" or "license" for more information.
    >>>> 1e-200**2
    Fernando> 0.0

According to the pow man page on my Mandrake 8.1 system it suggests that
ERANGE should be set if its first arg is zero.  This appears to happen when
x is around 1.5717e-162.  I suspect a bug in glibc (I have version 2.2.4).

In the region where the problem occurs, Python's float_pow() looks like

        PyFPE_START_PROTECT("pow", return NULL)
        ix = pow(iv, iw);
        PyFPE_END_PROTECT(ix)
        Py_SET_ERANGE_IF_OVERFLOW(ix);

Setting a break immediately after the pow() call shows that ERANGE is set
even though it appears to have correctly returned 0.  Perhaps if iv < 1, ix
== 0, and errno is ERANGE, errno should be cleared, at least for certain
versions of glibc?

-- 
Skip Montanaro (skip at pobox.com - http://www.mojam.com/)