shithub: opus

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Optimize biquad() to reduce dependency chains

--- a/dnn/lpcnet_enc.c

+++ b/dnn/lpcnet_enc.c

@@ -83,14 +83,25 @@

 static void biquad(float *y, float mem[2], const float *x, const float *b, const float *a, int N) {

   int i;

+  float mem0, mem1;

+  mem0 = mem[0];

+  mem1 = mem[1];

   for (i=0;i<N;i++) {

-    float xi, yi;

+    float xi, yi, mem00;

     xi = x[i];

-    yi = x[i] + mem[0];

-    mem[0] = mem[1] + (b[0]*xi - a[0]*yi);

-    mem[1] = (b[1]*xi - a[1]*yi);

+    yi = x[i] + mem0;

+    mem00 = mem0;

+    /* Original code:

+    mem0 = mem1 + (b[0]*xi - a[0]*yi);

+    mem1 = (b[1]*xi - a[1]*yi);

+    Modified to reduce dependency chains:

+    */

+    mem0 = (b[0]-a[0])*xi + mem1 - a[0]*mem0;

+    mem1 = (b[1]-a[1])*xi + 1e-30f - a[1]*mem00;

     y[i] = yi;

   }

+  mem[0] = mem0;

+  mem[1] = mem1;

 }

 #define celt_log10(x) (0.3010299957f*celt_log2(x))

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