shithub: audio-stretch

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- use unsigned ints to fix edge-case overflow possibility in find_period_fast()
- increase usable sample count range of merge_blocks() with unsigned calculation

--- a/stretch.c

+++ b/stretch.c

@@ -399,12 +399,12 @@

     }

     if (best_period * cnxt->num_chans * 2 != cnxt->shortest && best_period * cnxt->num_chans * 2 != cnxt->longest) {

-        int high_side_diff = cnxt->results [best_period] - cnxt->results [best_period+1];

-        int low_side_diff = cnxt->results [best_period] - cnxt->results [best_period-1];

+        unsigned int high_side_diff = cnxt->results [best_period] - cnxt->results [best_period+1];

+        unsigned int low_side_diff = cnxt->results [best_period] - cnxt->results [best_period-1];

-        if (low_side_diff > high_side_diff * 2)

+        if (low_side_diff / 2 > high_side_diff)

             best_period = best_period * 2 + 1;

-        else if (high_side_diff > low_side_diff * 2)

+        else if (high_side_diff / 2 > low_side_diff)

             best_period = best_period * 2 - 1;

         else

             best_period *= 2;

@@ -425,6 +425,11 @@

  * back to signed.  This is done to avoid the compression around zero that occurs

  * with calculations of this type on C implementations that round division toward

  * zero.

+ *

+ * The maximum period handled here without overflow possibility is 65535 samples.

+ * This corresponds to a maximum calculated period of 16383 samples (2x for stereo

+ * and 2x for the "2.0" version of the stretch algorithm). Since the maximum

+ * calculated period is currently set for 2400 samples, we have plenty of margin.

  */

 static void merge_blocks (short *output, short *input1, short *input2, int samples)

@@ -432,7 +437,6 @@

     int i;

     for (i = 0; i < samples; ++i)

-        output [i] = (((input1 [i] + 32768) * (samples - i) +

-            (input2 [i] + 32768) * i) / samples) - 32768;

+        output [i] = (int)(((unsigned int)(input1 [i] + 32768) * (samples - i) +

+            (unsigned int)(input2 [i] + 32768) * i) / samples) - 32768;

 }

-