A common cause of this is 32-bit x86 builds that use x87, which uses 80-bit precision which sounds like a good thing except that it only does it while values ar

A common cause of this is 32-bit x86 builds that use x87, which uses 80-bit precision which sounds like a good thing except that it only does it while values are in registers, which from the programmer's viewpoint means the precision might as well be fluctuating at random. Solution: don't use x87. There are a few compiler options for this, but the most obvious one is to just always build 64-bit.