PEP 238 (revised)

Tim Peters at
Mon Aug 6 07:41:15 CEST 2001

[Bengt Richter]
> UIAM, the way I read it, the only way you can get -0 from multiply
> is as a result of extreme underflow denormalizing to zero. Others
> give plain zero.  Of course, my intel pentium book is not the official
> ieee754 spec.

I can't guess what you're reading.  Here from the FMUL docs, in the IA-32
Intel Architecture Software Developer's Manual, Volume 2: Instruction Set
Reference, available at, e.g.,

The last (byte-serving) link will get you to it quickly w/o enduring a 6.7MB
download of the whole thing:

    The sign of the result is always the exclusive-OR of the source
    signs, even if one or more of the values being multiplied is 0 or
    [a graphic for infinity].

Same as the 754 rules.

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