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fixed-point: first check-point on quant_energy_mono() conversion

--- a/libcelt/quant_bands.c

+++ b/libcelt/quant_bands.c

@@ -39,35 +39,51 @@

 #include "os_support.h"

 #include "arch.h"

+#ifdef FIXED_POINT

+const float eMeans[24] = {11520, -2048, -3072, -640, 256, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};

+#else

 const float eMeans[24] = {45.f, -8.f, -12.f, -2.5f, 1.f, 0.f, 0.f, 0.f, 0.f, 0.f, 0.f, 0.f, 0.f, 0.f, 0.f, 0.f, 0.f, 0.f, 0.f, 0.f, 0.f, 0.f, 0.f, 0.f};

+#endif

 /*const int frac[24] = {4, 3, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2};*/

 const int frac[24] = {8, 6, 5, 4, 3, 3, 3, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2};

+#ifdef FIXED_POINT

+#define Q8 256.f

+#define Q8_1 (1.f/256.f)

+#else

+#define Q8 1.f

+#define Q8_1 1.f

+#endif

 static void quant_energy_mono(const CELTMode *m, celt_ener_t *eBands, celt_word16_t *oldEBands, int budget, ec_enc *enc)

 {

    int i;

    int bits;

-   float prev = 0;

+   celt_word16_t prev = 0;

    float coef = m->ePredCoef;

-   VARDECL(float *error);

+   VARDECL(celt_word16_t *error);

    /* The .7 is a heuristic */

    float beta = .7*coef;

-   ALLOC(error, m->nbEBands, float);

+   ALLOC(error, m->nbEBands, celt_word16_t);

    bits = ec_enc_tell(enc, 0);

    for (i=0;i<m->nbEBands;i++)

    {

       int qi;

-      float q;

-      float res;

-      float x;

-      float f;

-      float mean = (1-coef)*eMeans[i];

-      x = 20*log10(.3+ENER_SCALING_1*eBands[i]);

-      res = 6.;

-      f = (x-mean-coef*DB_SCALING_1*oldEBands[i]-prev)/res;

+      celt_word16_t q;   /* dB */

+      celt_word16_t res; /* dB */

+      celt_word16_t x;   /* dB */

+      celt_word16_t f;   /* Q8 */

+      celt_word16_t mean = (1-coef)*eMeans[i];

+      x = DB_SCALING*20*log10(.3+ENER_SCALING_1*eBands[i]);

+      res = DB_SCALING*6;

+      f = QCONST16(1.f,8)*(x-mean-coef*oldEBands[i]-prev*1.f)/res;

+#ifdef FIXED_POINT

+      /* Rounding to nearest integer here is really important! */

+      qi = (f+128)>>8;

+#else

       qi = (int)floor(.5+f);

+#endif

       /*ec_laplace_encode(enc, qi, i==0?11192:6192);*/

       /*ec_laplace_encode(enc, qi, 8500-i*200);*/

       /* If we don't have enough bits to encode all the energy, just assume something safe. */

@@ -76,13 +92,13 @@

       else

          ec_laplace_encode(enc, qi, 6000-i*200);

       q = qi*res;

-      error[i] = f - qi;

+      error[i] = f - SHL16(qi,8);

       /*printf("%d ", qi);*/

       /*printf("%f %f ", pred+prev+q, x);*/

       /*printf("%f ", x-pred);*/

-      oldEBands[i] = DB_SCALING*(mean+coef*DB_SCALING_1*oldEBands[i]+prev+q);

+      oldEBands[i] = mean+coef*oldEBands[i]+prev+q;

       prev = mean+prev+(1-beta)*q;

    }

@@ -91,7 +107,7 @@

    for (i=0;i<m->nbEBands;i++)

    {

       int q2;

-      float offset = (error[i]+.5)*frac[i];

+      float offset = Q8_1*(error[i]+QCONST16(.5f,8))*frac[i];

       /* FIXME: Instead of giving up without warning, we should degrade everything gracefully */

       if (ec_enc_tell(enc, 0) - bits +EC_ILOG(frac[i])> budget)

          break;

@@ -137,9 +153,9 @@

          qi = ec_laplace_decode(dec, 6000-i*200);

       q = qi*res;

-      oldEBands[i] = DB_SCALING*(mean+coef*DB_SCALING_1*oldEBands[i]+prev+q);

+      oldEBands[i] = DB_SCALING*(DB_SCALING_1*mean+coef*DB_SCALING_1*oldEBands[i]+prev+q);

-      prev = mean+prev+(1-beta)*q;

+      prev = DB_SCALING_1*mean+prev+(1-beta)*q;

    }

    for (i=0;i<m->nbEBands;i++)

    {