RE: problem with cos ( pi/2 )
RE: problem with cos ( pi/2 )
- Subject: RE: problem with cos ( pi/2 )
- From: billmonk <email@hidden>
- Date: Fri, 16 Jun 2006 11:55:36 -0500
Just to clarify two points...
1. cos( M_PI_2 ) == 6.123233995736766e-17, not 2.6484540326036093e-14
as I posted earlier. That value is the cosine an app-calculated pi/2
having less precision than M_PI_2.
2. It's true, these numbers -are- very close to zero. My questions are:
A) Is the '-llibm' compiler flag sufficient to use the IEEE math lib?
B) If it is, how come the results of cos( pi/2 ) don't agree with the
behavior documented in PowerPC Numerics, page 148? Am I doing
something else wrong? Googling, I see that some other math libs
(Java, for instance) document that one should -not- expect cos( pi/
2 ) to equal exactly zero. This is at variance with what PowerPC
Numerics says OS X does, however.
C) If the behavior documented in PowerPC Numerics doesn't actually
occur, what's the proper thing to do? The app has some fairly heavy
arithmetic going on, with the results displayed to the user both
graphically in text form. Should it round before drawing? Round
before displaying text? Both? What have others done in this situation?
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