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Re: Alternative math libraries
- To: "David S. Miller" <davem at redhat dot com>
- Subject: Re: Alternative math libraries
- From: Stephen L Moshier <moshier at mediaone dot net>
- Date: Fri, 25 May 2001 08:54:25 -0400 (EDT)
- cc: Bruce Allen <ballen at gravity dot phys dot uwm dot edu>, ballen at uwm dot edu, libc-alpha at sources dot redhat dot com
- Reply-To: moshier at moshier dot ne dot mediaone dot net
>> I was sure that linux glibc libm on Intel uses the actual x86
>> trigometric instructions to implement these routines.
>>
>> Later,
>> David S. Miller
>> davem@redhat.com
>
>That's correct. Those hardware instructions only give the correct
>answer when |x|<2^62.
No, that's not right. More marketing doubletalk. It's worse than
that. The incorrect answer threshold, for absolute measure, is about 2^18
for double precision and 2^47 for single precision. 2^62 is the
*totally* wrong answer threshold, where the error approaches 100%
and the hardware raises a flag.