It's an easy way to return nan and set FE_INVALID. If you're not worried about floating point exceptions you can just return NaN directly. Idk how much C# even guarantees about the floating point operations and if it's applicable there.
let me rephrase: data which you cannot guarantee meet the preconditions. Either the input is known good data or you sanitize it through some code path not compiled with fast-math.
Because the danger of fume is negligible. It's a thing if you put it in a 2m^2 storeroom and sniff the exhaust for 8 hours straight but in any other case it doesn't come close to concentrations you get on the street anyway.
The compiler is not beholden to the standard library but the standard. So all modern compilers come with a bit of knowledge of how standard library functions like memcpy are supposed to behave and as long as the visible effect is the same it's allowed to do anything it wants. So instead of calling the function memcpy for a size of 4, it can e.g. just use a mov instruction to move the value from a float to an integer register. [1] It does additional analysis on how the values are used and maybe it doesn't even need to move the value at all, but that's the gist of it.
A good example of this is the string functions in the C stdlib. I’ve reverse engineered some programs where the compiler used x86’s built-in “string” instructions instead of calling out to, say, `strlen`.
> I think the only reason people enjoy it is the fact that they have not gotten a chance to really spend time in a good tiling window manager on X11/GNU/Linux.
