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## Re: IEEE Inf and NaN support for numbers.c

**From**: |
Marius Vollmer |

**Subject**: |
Re: IEEE Inf and NaN support for numbers.c |

**Date**: |
07 May 2002 00:39:25 +0200 |

**User-agent**: |
Gnus/5.09 (Gnus v5.9.0) Emacs/21.2 |

Marius Vollmer <address@hidden> writes:
>* Ok. I think we should follow PLT Scheme here. I will apply your*
>* patch and make the necessary changes.*
Done. Please play with it and tell me whether you like the changes I
made.
numbers.c (mem2ureal): Recognize "inf.0" and "nan.xxx".
(scm_even_p, scm_odd_p): Treat infinity as even and odd.
(iflo2str): Don't output a '+' for negative numbers or for Inf and
NaN. They will provide their own sign.
(scm_divide): Only allow divides by inexact zeros. Dividing by
exact zeros still signals an errors.
Here is the NEWS entry:
** There is support for Infinity and NaNs.
Following PLT Scheme, Guile can now work with infinite numbers and
'not-a-numbers'.
There is new syntax for numbers: "+inf.0" (infinity), "-inf.0"
(negative infinity), "+nan.0" (not-a-number), and "-nan.0" (same as
"+nan.0"). These numbers are inexact and have no exact counterpart.
Dividing by an inexact zero returns +inf.0 or -inf.0, depending on the
sign of the dividend. The infinities are integers, and they answer #t
for both 'even?' and 'odd?'. The +nan.0 value is not an integer and is
not '=' to itself, but '+nan.0' is 'eqv?' to itself.
For example
(/ 1 0.0)
=> +inf.0
(/ 0 0.0)
=> +nan.0
(/ 0)
ERROR: Numerical overflow
PLT Scheme does also distinguish plus and minus zero:
(= 0.0 -0.0)
=> #t
but
(eqv? 0.0 -0.0)
=> #f
I think we should do this as well. John, how would one test for the
sign of zero?

**Re: IEEE Inf and NaN support for numbers.c**,
*Marius Vollmer* **<=**