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Avoid sin()/cos() calls for pitch reference

--- a/dnn/fwgan.c

+++ b/dnn/fwgan.c

@@ -48,15 +48,34 @@

 #define FWGAN_FEATURES (NB_FEATURES-1)

-static void pitch_embeddings(float *pembed, double *phase, double w0) {

+static void pitch_embeddings(float *pembed, float *phase, double w0) {

   int i;

-  /* FIXME: This could be speeded up by making phase a unit-norm complex value, rotating it

-     by exp(-i*w0) each sample, and renormalizing once in while.  */

+  float wreal, wimag;

+#if 1

+  /* This Taylor expansion should be good enough since w0 is always small. */

+  float w2 = w0*w0;

+  wreal = 1 - .5*w2*(1.f - 0.083333333f*w2);

+  wimag = w0*(1 - 0.166666667f*w2*(1.f - 0.05f*w2));

+#else

+  wreal = cos(w0);

+  wimag = sin(w0);

+#endif

+  /* Speed-up phase reference by making phase a unit-norm complex value and rotating it

+     by exp(-i*w0) each sample.  */

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

-    *phase += w0;

-    pembed[i] = sin(*phase);

-    pembed[SUBFRAME_SIZE+i] = cos(*phase);

+    float tmp;

+    tmp = phase[0]*wreal - phase[1]*wimag;

+    phase[1] = phase[0]*wimag + phase[1]*wreal;

+    phase[0] = tmp;

+    pembed[i] = phase[1];

+    pembed[SUBFRAME_SIZE+i] = phase[0];

   }

+  /* Renormalize once per sub-frame, though we could probably do it even less frequently. */

+  {

+    float r = 1.f/sqrt(phase[0]*phase[0] + phase[1]*phase[1]);

+    phase[0] *= r;

+    phase[1] *= r;

+  }

 }

 static void run_fwgan_upsampler(FWGANState *st, float *cond, const float *features)

@@ -76,6 +95,7 @@

   float tmp1[MAX_CONT_SIZE];

   float tmp2[MAX_CONT_SIZE];

   FWGAN *model;

+  st->embed_phase[0] = 1;

   model = &st->model;

   norm2 = celt_inner_prod(pcm0, pcm0, CONT_PCM_INPUTS, st->arch);

   norm_1 = 1.f/sqrt(1e-8f + norm2);

@@ -158,7 +178,7 @@

   FWGAN *model;

   model = &st->model;

-  pitch_embeddings(pembed, &st->embed_phase, w0);

+  pitch_embeddings(pembed, st->embed_phase, w0);

   /* Interleave bfcc_cond and pembed for each subframe in feat_in. */

   OPUS_COPY(&feat_in[BFCC_WITH_CORR_UPSAMPLER_FC_OUT_SIZE/4], &cond[0], BFCC_WITH_CORR_UPSAMPLER_FC_OUT_SIZE/4);

   OPUS_COPY(&feat_in[0], &pembed[0], FWGAN_FRAME_SIZE/2);

--- a/dnn/fwgan.h

+++ b/dnn/fwgan.h

@@ -45,7 +45,7 @@

   FWGAN model;

   int arch;

   int cont_initialized;

-  double embed_phase;

+  float embed_phase[2];

   float last_gain;

   float last_lpc[LPC_ORDER];

   float syn_mem[LPC_ORDER];

-- 

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