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fixed-point: added cheap celt_div() division using a reciprocal

--- a/libcelt/bands.c

+++ b/libcelt/bands.c

@@ -126,7 +126,7 @@

          shift = celt_zlog2(bank[i*C+c])-13;

          E = VSHR32(bank[i*C+c], shift);

          if (E>0)

-            g = DIV32_16(QCONST32(1.f,28),MULT16_16_Q14(E,sqrtC_1[C-1]));

+            g = EXTRACT16(celt_div(QCONST32(1.f,28),MULT16_16_Q14(E,sqrtC_1[C-1])));

          else

             g = 0;

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

@@ -257,7 +257,7 @@

          residual doesn't quantise well */

       Sxy = MULT16_32_Q15(QCONST16(.9f, 15), Sxy);

       /* gain = Sxy/Sxx */

-      gains[i] = DIV32_16(Sxy,ADD32(SHR32(Sxx, PGAIN_SHIFT),EPSILON));

+      gains[i] = EXTRACT16(celt_div(Sxy,ADD32(SHR32(Sxx, PGAIN_SHIFT),EPSILON)));

       /*printf ("%f ", 1-sqrt(1-gain*gain));*/

    }

    /*if(rand()%10==0)

--- a/libcelt/mathops.h

+++ b/libcelt/mathops.h

@@ -45,6 +45,7 @@

 #define celt_cos_norm(x) (cos((.5f*M_PI)*(x)))

 #define celt_atan atan

 #define celt_rcp(x) (1.f/(x))

+#define celt_div(a,b) ((a)/(b))

 #endif

@@ -201,6 +202,8 @@

       frac = -frac;

    return VSHR32(EXTEND32(frac),i-16);

 }

+

+#define celt_div(a,b) MULT32_32_Q31(a,celt_rcp(b))

 #endif /* FIXED_POINT */

--- a/libcelt/quant_bands.c

+++ b/libcelt/quant_bands.c

@@ -106,7 +106,7 @@

       celt_word16_t f;   /* Q8 */

       celt_word16_t mean = MULT16_16_Q15(Q15ONE-coef,eMeans[i]);

       x = amp2dB(eBands[i]);

-      f = DIV32_16(SHL32(EXTEND32(x-mean-MULT16_16_Q15(coef,oldEBands[i])-prev),8),base_resolution);

+      f = EXTRACT16(celt_div(SHL32(EXTEND32(x-mean-MULT16_16_Q15(coef,oldEBands[i])-prev),8),base_resolution));

 #ifdef FIXED_POINT

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

       qi = (f+128)>>8;

@@ -149,7 +149,7 @@

       if (q2 > frac[i]-1)

          q2 = frac[i]-1;

       ec_enc_uint(enc, q2, frac[i]);

-      offset = DIV32_16(SHL16(q2,8)+QCONST16(.5,8),frac[i])-QCONST16(.5f,8);

+      offset = EXTRACT16(celt_div(SHL16(q2,8)+QCONST16(.5,8),frac[i])-QCONST16(.5f,8));

       oldEBands[i] += PSHR32(MULT16_16(DB_SCALING*6,offset),8);

       /*printf ("%f ", error[i] - offset);*/

    }

@@ -199,7 +199,7 @@

       if (ec_dec_tell(dec, 0) - bits +EC_ILOG(frac[i])> budget)

          break;

       q2 = ec_dec_uint(dec, frac[i]);

-      offset = DIV32_16(SHL16(q2,8)+QCONST16(.5,8),frac[i])-QCONST16(.5f,8);

+      offset = EXTRACT16(celt_div(SHL16(q2,8)+QCONST16(.5,8),frac[i])-QCONST16(.5f,8));

       oldEBands[i] += PSHR32(MULT16_16(DB_SCALING*6,offset),8);

    }

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

--- a/libcelt/vq.c

+++ b/libcelt/vq.c

@@ -378,7 +378,7 @@

          xy = MAC16_16(xy, x[j], Y[i+N-j-1]);

          yy = MAC16_16(yy, Y[i+N-j-1], Y[i+N-j-1]);

       }

-      score = DIV32(MULT16_16(ROUND16(xy,14),ROUND16(xy,14)), ROUND16(yy,14));

+      score = celt_div(MULT16_16(ROUND16(xy,14),ROUND16(xy,14)), ROUND16(yy,14));

       if (score > best_score)

       {

          best_score = score;