shithub: sox

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speed up small-factor downsampling; e.g. ~15% improvement for 48k->44100

--- a/src/rate.c

+++ b/src/rate.c

@@ -313,9 +313,9 @@

     double d, epsilon = 0, frac;

     upsample = arbM < 1;

     for (i = arbM * .5, shift = 0; i >>= 1; arbM *= .5, ++shift);

-    preM = 1 - (arbM > 2);

-    postM = 1 + (arbM > 1 && arbM < 2), arbM /= postM;

-    preL = 1 + (upsample && mode), arbM *= preL;

+    preM = upsample || (arbM > 1.5 && arbM < 2);

+    postM = 1 + (arbM > 1 && preM), arbM /= postM;

+    preL = 1 + (!preM && arbM < 2) + (upsample && mode), arbM *= preL;

     if ((frac = arbM - (int)arbM))

       epsilon = fabs((uint32_t)(frac * MULT32 + .5) / (frac * MULT32) - 1);

     for (i = 1, rational = !frac; i <= maxL && !rational; ++i) {