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(parent: db4096c) | patch
math: change the formula used for acos.s
authornsz <nsz@port70.net>
Fri, 4 May 2012 23:11:56 +0000 (01:11 +0200)
committernsz <nsz@port70.net>
Fri, 4 May 2012 23:11:56 +0000 (01:11 +0200)
commitf697d66b81912af59128ac1b96bc0e2a4514b758
tree32433a4df7d33f692afa2ff6e759fa1c5870b8f0tree | snapshot
parentdb4096c5f2ffb15e52015004ab5a900b820c6683commit | diff
math: change the formula used for acos.s

old: 2*atan2(sqrt(1-x),sqrt(1+x))
new: atan2(fabs(sqrt((1-x)*(1+x))),x)
improvements:
* all edge cases are fixed (sign of zero in downward rounding)
* a bit faster (here a single call is about 131ns vs 162ns)
* a bit more precise (at most 1ulp error on 1M uniform random
samples in [0,1), the old formula gave some 2ulp errors as well)
src/math/i386/acos.s diff | blob | history
src/math/x86_64/acosl.s diff | blob | history
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