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Using log approximations

--- a/dnn/common.h

+++ b/dnn/common.h

@@ -12,6 +12,26 @@

 float lpc_from_cepstrum(float *lpc, const float *cepstrum);

+#define LOG256 5.5451774445f

+static RNN_INLINE float log2_approx(float x)

+{

+   int integer;

+   float frac;

+   union {

+      float f;

+      int i;

+   } in;

+   in.f = x;

+   integer = (in.i>>23)-127;

+   in.i -= integer<<23;

+   frac = in.f - 1.5f;

+   frac = -0.41445418f + frac*(0.95909232f

+          + frac*(-0.33951290f + frac*0.16541097f));

+   return 1+integer+frac;

+}

+

+#define log_approx(x) (0.69315f*log2_approx(x))

+

 static RNN_INLINE float ulaw2lin(float u)

 {

     float s;

@@ -19,7 +39,7 @@

     u = u - 128;

     s = u >= 0 ? 1 : -1;

     u = fabs(u);

-    return s*scale_1*(exp(u/128.*log(256))-1);

+    return s*scale_1*(exp(u/128.*LOG256)-1);

 }

 static RNN_INLINE int lin2ulaw(float x)

@@ -28,7 +48,7 @@

     float scale = 255.f/32768.f;

     int s = x >= 0 ? 1 : -1;

     x = fabs(x);

-    u = (s*(128*log(1+scale*x)/log(256)));

+    u = (s*(128*log_approx(1+scale*x)/LOG256));

     u = 128 + u;

     if (u < 0) u = 0;

     if (u > 255) u = 255;

--- a/dnn/dump_data.c

+++ b/dnn/dump_data.c

@@ -219,7 +219,7 @@

     /* Excitation out. */

     data[4*i+3] = e;

     /* Simulate error on excitation. */

-    noise = (int)floor(.5 + noise_std*.707*(log((float)rand()/RAND_MAX)-log((float)rand()/RAND_MAX)));

+    noise = (int)floor(.5 + noise_std*.707*(log_approx((float)rand()/RAND_MAX)-log_approx((float)rand()/RAND_MAX)));

     e += noise;

     e = IMIN(255, IMAX(0, e));

-- 

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