rygorous

// float->half variants.
// by Fabian "ryg" Giesen.
//
// I hereby place this code in the public domain, as per the terms of the
// CC0 license:
//
//   https://creativecommons.org/publicdomain/zero/1.0/
//
// float_to_half_full: This is basically the ISPC stdlib code, except
// I preserve the sign of NaNs (any good reason not to?)