Delaying the softmax() to avoid the pow()

Now at 5x real-time, with all the low-hanging fruit done.

Author: jmvalin

src/nnet.c

@@ -39,6 +39,8 @@
 #include "nnet.h"
 #include "nnet_data.h"
 
+#define SOFTMAX_HACK
+
 #ifdef __AVX2__
 #include <immintrin.h>
 static __m256 exp8_approx(__m256 X)
@@ -340,6 +342,10 @@ void compute_activation(float *output, float *input, int N, int activation)
       for (i=0;i<N;i++)
          output[i] = relu(input[i]);
    } else if (activation == ACTIVATION_SOFTMAX) {
+#ifdef SOFTMAX_HACK
+      for (i=0;i<N;i++)
+         output[i] = input[i];
+#else
       float sum = 0;
       softmax(output, input, N);
       for (i=0;i<N;i++) {
@@ -348,6 +354,7 @@ void compute_activation(float *output, float *input, int N, int activation)
       sum = 1.f/(sum+1e-30);
       for (i=0;i<N;i++)
          output[i] = sum*output[i];
+#endif
    } else {
       celt_assert(activation == ACTIVATION_LINEAR);
       for (i=0;i<N;i++)
@@ -619,12 +626,24 @@ int sample_from_pdf(const float *pdf, int N, float exp_boost, float pdf_floor)
     float tmp[DUAL_FC_OUT_SIZE];
     celt_assert(N <= DUAL_FC_OUT_SIZE);
     sum = 0;
+#ifdef SOFTMAX_HACK
+    for (i=0;i<N;i++)
+    {
+        tmp[i] = pdf[i] * (1.f+exp_boost);
+    }
+    softmax(tmp, tmp, N);
+    for (i=0;i<N;i++)
+    {
+        sum += tmp[i];
+    }
+#else
     /* Decrease the temperature of the sampling. */
     for (i=0;i<N;i++)
     {
         tmp[i] = pow(pdf[i], 1.f+exp_boost);
         sum += tmp[i];
     }
+#endif
     norm = 1.f/sum;
     /* Convert tmp to a CDF while subtracting the floor */
     tmp[0] = MAX16(0, norm*tmp[0] - pdf_floor);