Hello everyone.

My apologies if this isn't the place to post my question. I couldn't find a forum on general x86 questions. Feel free to relocate it to a more appropriate place.

The x87 FPU specs say that FSIN and FCOS can compute any angle in the range \\pm 2^63, which is roughly \\pm 1E18. My tests showed that even for smaller arguments, say in the order of 1E10, they produce results that are correct only for the first 10 digits and the rest are all wrong.

My question is, how accurate are the computations of FSIN and FCOS? Since they operate on the stack register, which is 80bit wide, shouldn't they at least provide correct double precision results ?

I can provide code samples, if asked.

Best regards,

Stathis