[gpderetta]

there is some amount of truth on what the parent is saying. Ages ago, when x86 only had x87 FP, gcc would program the FPU to use 80 bit precision even when dealing with doubles. The excess precision meant that GCC could not implement IEEE math correctly even without fast-math. Forcing the storing of intermediate values into memory via volatile variables was a partial solution to this problem.

MSVC configures the FPU to use 64 bit precision which means that double words fine, but it has no 80 bit long double and float still suffer from excess precision.

SSE avoid all these problems.

[vlovich123]

Kind of, but that still shouldn't have impacted Kahan summation, which only cares about associativity, and extended precision doesn't impact that. They would just end up getting more numerically accurate results on x87.