On 02/17/2010 02:43 PM, Andrew Haley wrote: > On 02/17/2010 02:26 PM, Vincent Lefevre wrote: >> On 2010-02-16 15:39:31 +0100, Christoph Groth wrote: >>> Thank you all very much for clarifying this issue. I am very much >>> surprised that x87 instructions behave differently on AMD and Intel >>> processors but this seems indeed to be the case. >> >> That's for elementary functions only (e.g. fsincos here). On >> >> http://www.vinc17.net/research/testlibm/ >> >> you can see that different platforms give different results. >> Differencies may be due to the OS, the C library and/or the >> hardware. >> >> Note that on x86_64 machines, sin and cos are correctly rounded >> (this is not proved, but probably true in practice, assuming no >> bugs in the implementation). I wonder why GCC doesn't use these >> functions by default instead of glibc's sincos (which could be >> enabled only with an option like -ffast-math). > > Maybe this is a bug. There is a version of sincos in the IBM Accurate > Mathematical Library but it's not used in this case. I misspoke. There is a file there called sincos.c, but no sincos(). Seems to me like calling an inaccurate sincos() when the user tried to call an accurate sin() and cos() is surely a bug. Andrew.
