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387 numerical instability

Whilst reading the GCC man page documentation for the -mfpmath option, I came across this sentence for -mfpmath=sse:

The resulting code should be considerably faster in the major-
ity of cases and avoid the numerical instability problems of
387 code, but may break some existing code that expects tempo-
raries to be 80bit.

Can someone point me to a description of these "numerical instability problems of 387 code", please?

I've searched the GCC site & mailing lists, and I've searched with Google, but I can't find anything that details the particular concerns that led to this note in the manual. All I can find is a list message containing the patch that put it into the man page.

GCC is version 3.3.5 on this system.

Neil.

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