Hello!
Fair enough, so with 64 bit floats you have no right to expect an
accurate answer for sin(2^90). However, you DO have a right to expect
an answer in the range [-1,+1] rather than the 1.2e+27 that Richard
quoted. I see no words in the description of
-funsafe-math-optimizations to lead me to expect such a result.
The source operand to fsin, fcos and fsincos x87 insns must be within
the range of +-2^63, otherwise a C2 flag is set in FP status word that
marks insufficient operand reduction. Limited operand range is the
reason, why fsin & friends are enabled only with
-funsafe-math-optimizations.
However, the argument to fsin can be reduced to an acceptable range by
using fmod builtin. Internally, this builtin is implemented as a very
tight loop that check for insufficient reduction, and could reduce
whatever finite value one wishes.
Out of curiosity, where could sin(2^90) be needed? It looks rather big
angle to me.
Uros.
