dominikh's comments

If 0.02 is the JND of deltaEOK, how come everybody is getting results an order of magnitude smaller? Even the author himself (at https://www.keithcirkel.co.uk/too-much-color/) says they get 0.0028, but never elaborate on the significance of that result.

Note that the source you're seeing there is the fallback implementation, which is only used if there is no instruction for FMA in the architecture you're compiling for. On AMD64, for example, the call to math.FMA will be replaced by the VFMADD231SD instruction.