shithub: opus

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Changed the pulse spreading rotations so that the number of iterations is
variable instead of the angle. Should now be both less CPU-intensive and
makes fixed-point code simpler.

--- a/libcelt/bands.c

+++ b/libcelt/bands.c

@@ -41,13 +41,13 @@

 #include "os_support.h"

 #include "mathops.h"

-void exp_rotation(celt_norm_t *X, int len, celt_word16_t theta, int dir, int stride, int iter)

+void exp_rotation(celt_norm_t *X, int len, int dir, int stride, int iter)

 {

    int i, k;

    celt_word16_t c, s;

-   /* c = cos(theta); s = dir*sin(theta); but we're approximating here for small theta */

-   c = Q15ONE-MULT16_16_Q15(QCONST16(.5f,15),MULT16_16_Q15(theta,theta));

-   s = dir*theta;

+   /* Equivalent to cos(.3) and sin(.3) */

+   c = QCONST16(0.95534,15);

+   s = dir*QCONST16(0.29552,15);

    for (k=0;k<iter;k++)

    {

       /* We could use MULT16_16_P15 instead of MULT16_16_Q15 for more accuracy, 

@@ -255,11 +255,11 @@

       if (q > 0)

       {

-         celt_word16_t theta = DIV32_16(MULT16_16_16(QCONST16(.007f,15),B*(eBands[i+1]-eBands[i])),q);

-         exp_rotation(P+B*eBands[i], B*(eBands[i+1]-eBands[i]), theta, -1, B, 8);

-         exp_rotation(X+B*eBands[i], B*(eBands[i+1]-eBands[i]), theta, -1, B, 8);

+         int nb_rotations = (B*(eBands[i+1]-eBands[i])+4*q)/(8*q);

+         exp_rotation(P+B*eBands[i], B*(eBands[i+1]-eBands[i]), -1, B, nb_rotations);

+         exp_rotation(X+B*eBands[i], B*(eBands[i+1]-eBands[i]), -1, B, nb_rotations);

          alg_quant(X+B*eBands[i], W+B*eBands[i], B*(eBands[i+1]-eBands[i]), q, P+B*eBands[i], alpha, enc);

-         exp_rotation(X+B*eBands[i], B*(eBands[i+1]-eBands[i]), theta, 1, B, 8);

+         exp_rotation(X+B*eBands[i], B*(eBands[i+1]-eBands[i]), 1, B, nb_rotations);

       }

       for (j=B*eBands[i];j<B*eBands[i+1];j++)

          norm[j] = MULT16_16_Q15(n,X[j]);

@@ -316,10 +316,10 @@

       if (q > 0)

       {

-         celt_word16_t theta = DIV32_16(MULT16_16_16(QCONST16(.007f,15),B*(eBands[i+1]-eBands[i])),q);

-         exp_rotation(P+B*eBands[i], B*(eBands[i+1]-eBands[i]), theta, -1, B, 8);

+         int nb_rotations = (B*(eBands[i+1]-eBands[i])+4*q)/(8*q);

+         exp_rotation(P+B*eBands[i], B*(eBands[i+1]-eBands[i]), -1, B, nb_rotations);

          alg_unquant(X+B*eBands[i], B*(eBands[i+1]-eBands[i]), q, P+B*eBands[i], alpha, dec);

-         exp_rotation(X+B*eBands[i], B*(eBands[i+1]-eBands[i]), theta, 1, B, 8);

+         exp_rotation(X+B*eBands[i], B*(eBands[i+1]-eBands[i]), 1, B, nb_rotations);

       }

       for (j=B*eBands[i];j<B*eBands[i+1];j++)

          norm[j] = MULT16_16_Q15(n,X[j]);

--- a/libcelt/bands.h

+++ b/libcelt/bands.h

@@ -41,7 +41,7 @@

 /** Applies a series of rotations so that pulses are spread like a two-sided

 exponential. The effect of this is to reduce the tonal noise created by the

 sparse spectrum resulting from the pulse codebook */

-void exp_rotation(celt_norm_t *X, int len, celt_word16_t theta, int dir, int stride, int iter);

+void exp_rotation(celt_norm_t *X, int len, int dir, int stride, int iter);

 /** Normalise each band of X such that the energy in each band is 

     equal to 1

--- a/tests/rotation-test.c

+++ b/tests/rotation-test.c

@@ -13,31 +13,37 @@

 void test_rotation(int N, int K)

 {

    int i;

-   double err = 0, ener = 0, snr;

-   celt_word16_t theta = Q15_ONE*.007*N/K;

+   double err = 0, ener = 0, snr, snr0;

    celt_word16_t x0[MAX_SIZE];

    celt_word16_t x1[MAX_SIZE];

+   int nb_rotations = (N+4*K)/(8*K);

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

       x1[i] = x0[i] = rand()%32767-16384;

-   exp_rotation(x1, N, theta, 1, 1, 8);

-   exp_rotation(x1, N, theta, -1, 1, 8);

+   exp_rotation(x1, N, 1, 1, nb_rotations);

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

    {

       err += (x0[i]-(double)x1[i])*(x0[i]-(double)x1[i]);

       ener += x0[i]*(double)x0[i];

    }

+   snr0 = 20*log10(ener/err);

+   err = ener = 0;

+   exp_rotation(x1, N, -1, 1, nb_rotations);

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

+   {

+      err += (x0[i]-(double)x1[i])*(x0[i]-(double)x1[i]);

+      ener += x0[i]*(double)x0[i];

+   }

    snr = 20*log10(ener/err);

-   printf ("SNR for size %d (%d pulses) is %f\n", N, K, snr);

-   if (snr < 60)

+   printf ("SNR for size %d (%d pulses) is %f (was %f without inverse)\n", N, K, snr, snr0);

+   if (snr < 60 || snr0 > 20)

       ret = 1;

 }

 int main()

 {

-   test_rotation(4, 40);

-   test_rotation(7, 20);

-   test_rotation(10, 10);

+   test_rotation(15, 3);

    test_rotation(23, 5);

    test_rotation(50, 3);

+   test_rotation(80, 1);

    return ret;

 }