On Tue, 31 Jan 2023 at 15:05, Joel Jacobson <j...@compiler.org> wrote: > > I also think the performance impact no matter how small isn't worth it, > but a comment based on your comments would be very valuable IMO. > > Below is an attempt at summarising your text, and to avoid the performance > impact, > maybe an #if so we get the general correct formula for DEC_DIGITS 1 or 2, > and the reduced hand-optimised form for DEC_DIGITS 4? > That could also improve readabilty, since readers perhaps more easily would > see > the relation between sweight and arg.weight, for the only DEC_DIGITS case we > care about. >
That seems a bit wordy, given the context of this comment. I think it's sufficient to just give the formula, and note that it simplifies when DEC_DIGITS is even (not just 4): /* * Assume the input was normalized, so arg.weight is accurate. The result * then has at least sweight = floor(arg.weight * DEC_DIGITS / 2 + 1) * digits before the decimal point. When DEC_DIGITS is even, we can save * a few cycles, since the division is exact and there is no need to * round down. */ #if DEC_DIGITS == ((DEC_DIGITS / 2) * 2) sweight = arg.weight * DEC_DIGITS / 2 + 1; #else if (arg.weight >= 0) sweight = arg.weight * DEC_DIGITS / 2 + 1; else sweight = 1 - (1 - arg.weight * DEC_DIGITS) / 2; #endif Regards, Dean