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src/spectral/dct_ooura.c: further optimize by computing scaling factors once

--- a/src/spectral/dct_ooura.c

+++ b/src/spectral/dct_ooura.c

@@ -30,6 +30,7 @@

   fvec_t *input;

   smpl_t *w;

   int *ip;

+  smpl_t scalers[5];

 };

 aubio_dct_t * new_aubio_dct (uint_t size) {

@@ -44,6 +45,11 @@

   s->w = AUBIO_ARRAY(smpl_t, s->size * 5 / 4);

   s->ip = AUBIO_ARRAY(int, 3 + (1 << (int)FLOOR(LOG(s->size/2) / LOG(2))) / 2);

   s->ip[0] = 0;

+  s->scalers[0] = 2. * SQRT(1./(4.*s->size));

+  s->scalers[1] = 2. * SQRT(1./(2.*s->size));

+  s->scalers[2] = 1. / s->scalers[0];

+  s->scalers[3] = 1. / s->scalers[1];

+  s->scalers[4] = 2. / s->size;

   return s;

 beach:

   AUBIO_FREE(s);

@@ -62,9 +68,9 @@

   fvec_copy(input, s->input);

   aubio_ooura_ddct(s->size, -1, s->input->data, s->ip, s->w);

   // apply orthonormal scaling

-  s->input->data[0] *= 2.* SQRT(1./(4.*s->input->length));

+  s->input->data[0] *= s->scalers[0];

   for (i = 1; i < s->input->length; i++) {

-    s->input->data[i] *= 2. * SQRT(1./(2.*s->input->length));

+    s->input->data[i] *= s->scalers[1];

   }

   fvec_copy(s->input, output);

 }

@@ -72,14 +78,14 @@

 void aubio_dct_rdo(aubio_dct_t *s, const fvec_t *input, fvec_t *output) {

   uint_t i = 0;

   fvec_copy(input, s->input);

-  s->input->data[0] /= 2.* SQRT(1./(4.*s->input->length));

+  s->input->data[0] *= s->scalers[2];

   for (i = 1; i < s->input->length; i++) {

-    s->input->data[i] /= 2. * SQRT(1./(2.*s->input->length));

+    s->input->data[i] *= s->scalers[3];

   }

   s->input->data[0] *= .5;

   aubio_ooura_ddct(s->size, 1, s->input->data, s->ip, s->w);

   for (i = 0; i < s->input->length; i++) {

-    s->input->data[i] *= 2./s->input->length;

+    s->input->data[i] *= s->scalers[4];

   }

   fvec_copy(s->input, output);

 }