c5964538b7
function approximation for the second step. The polynomial has degree 2 for cbrtf() and 4 for cbrt(). These degrees are minimal for the final accuracy to be essentially the same as before (slightly smaller). Adjust the rounding between steps 2 and 3 to match. Unfortunately, for cbrt(), this breaks the claimed accuracy slightly although incorrect rounding doesn't. Claim less accuracy since its not worth pessimizing the polynomial or relying on exhaustive testing to get insignificantly more accuracy. This saves about 30 cycles on Athlons (mainly by avoiding 2 divisions) so it gives an overall optimization in the 10-25% range (a larger percentage for float precision, especially in 32-bit mode, since other overheads are more dominant for double precision, surprisingly more in 32-bit mode). |
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