> There is nothing in the C standard which makes that invalid. C only permits¹ optimizations that do not change semantics, so changing the result of a floating

> There is nothing in the C standard which makes that invalid. C only permits¹ optimizations that do not change semantics, so changing the result of a floating point expression is invalid. Example 5 on p16 of C11² makes this explicit: “Rearrangement for floating-point expressions is often restricted because of limitations in precision as well as range. The implementation cannot generally apply the mathematical associative rules for addition or multiplication, nor the distributive rule, because of roundoff error, even in the absence of overflow and underflow. Likewise, implementations cannot generally replace decimal constants in order to rearrange expressions.” ¹ Of course many compilers have options that invoke something other than standard-conforming C. ² C11 final draft: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf