c++ - acos(double) gives different result on x64 and x32 Visual Studio

Question

acos(double) gives different result on x64 and x32 Visual Studio.

printf("%.30g
", double(acosl(0.49990774364240564)));
printf("%.30g
", acos(0.49990774364240564));

on x64: 1.0473040763868076
on x32: 1.0473040763868078

on linux4.4 x32 and x64 with sse enabled: 1.0473040763868078

is there a way to make VSx64 acos() give me 1.0473040763868078 as result?

Answer 1

You may have reached the precision limit. Double precision is approximately 16 digits. After, there is no guarantee the digits are valid. If so, you cannot change this behavior, except changing the type double to something else, supporting higher precision.

E.g. long double if your machine and compiler supports the extended 80 bit double or 128 bit Quadruple (also machine depended see here for example).