The processor itself supports configuring some aspects of floating point behavior; on x86 this is the MXCSR register. The most important one is rounding mode:

The processor itself supports configuring some aspects of floating point behavior; on x86 this is the MXCSR register. The most important one is rounding mode: you can choose round-to-nearest, round-down, round-up, or round-towards-zero. Less common options include whether to raise an exception on various out-of-range conditions, and whether to treat denormal numbers as zero (faster but less accurate and not IEEE 754 compliant). The C standard library has functions to do this configuration; search for fesetenv. _fpreset is not a standard function but, at least in Wine's implementation [1], just resets the relevant configuration registers to an initial state. [1] https://github.com/wine-mirror/wine/blob/e909986e6ea5ecd49b2b847f321ad89b2ae4f6f1/dlls/msvcrt/math.c#L2139 https://github.com/wine-mirror/wine/blob/e909986e6ea5ecd49b2...