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Simplifies vector renormalisation (and using it less)

--- a/libcelt/bands.c

+++ b/libcelt/bands.c

@@ -177,7 +177,7 @@

    for (c=0;c<C;c++)

    {

       i=0; do {

-         renormalise_vector(X+M*eBands[i]+c*M*m->shortMdctSize, Q15ONE, M*eBands[i+1]-M*eBands[i], 1);

+         renormalise_vector(X+M*eBands[i]+c*M*m->shortMdctSize, M*eBands[i+1]-M*eBands[i]);

       } while (++i<end);

    }

 }

@@ -563,8 +563,12 @@

             if (stereo)

                stereo_band_mix(m, X, Y, bandE, 0, i, 1, N);

-            mid = renormalise_vector(X, Q15ONE, N, 1);

-            side = renormalise_vector(Y, Q15ONE, N, 1);

+            mid = vector_norm(X, N);

+            side = vector_norm(Y, N);

+            /* TODO: Renormalising X and Y *may* help fixed-point a bit at very high rate.

+                     Let's do that at higher complexity */

+            /*mid = renormalise_vector(X, Q15ONE, N, 1);

+            side = renormalise_vector(Y, Q15ONE, N, 1);*/

             /* theta is the atan() of the ratio between the (normalized)

                side and mid. With just that parameter, we can re-scale both

@@ -801,8 +805,8 @@

          stereo_band_mix(m, X, Y, bandE, 0, i, -1, N);

          /* We only need to renormalize because quantization may not

             have preserved orthogonality of mid and side */

-         renormalise_vector(X, Q15ONE, N, 1);

-         renormalise_vector(Y, Q15ONE, N, 1);

+         renormalise_vector(X, N);

+         renormalise_vector(Y, N);

       }

    }

 }

--- a/libcelt/vq.c

+++ b/libcelt/vq.c

@@ -191,7 +191,7 @@

             X[j] = (int)(*seed)>>20;

          }

       }

-      renormalise_vector(X, Q15ONE, N, 1);

+      renormalise_vector(X, N);

       return;

    }

    K = get_pulses(K);

@@ -368,7 +368,7 @@

             X[i] = (int)(*seed)>>20;

          }

       }

-      renormalise_vector(X, Q15ONE, N, 1);

+      renormalise_vector(X, N);

       return;

    }

    K = get_pulses(K);

@@ -384,9 +384,22 @@

    RESTORE_STACK;

 }

-celt_word16 renormalise_vector(celt_norm *X, celt_word16 value, int N, int stride)

+celt_word16 vector_norm(const celt_norm *X, int N)

 {

    int i;

+   celt_word32 E = EPSILON;

+   const celt_norm *xptr = X;

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

+   {

+      E = MAC16_16(E, *xptr, *xptr);

+      xptr++;

+   }

+   return celt_sqrt(E);

+}

+

+void renormalise_vector(celt_norm *X, int N)

+{

+   int i;

 #ifdef FIXED_POINT

    int k;

 #endif

@@ -397,20 +410,20 @@

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

    {

       E = MAC16_16(E, *xptr, *xptr);

-      xptr += stride;

+      xptr++;

    }

 #ifdef FIXED_POINT

    k = celt_ilog2(E)>>1;

 #endif

    t = VSHR32(E, (k-7)<<1);

-   g = MULT16_16_Q15(value, celt_rsqrt_norm(t));

+   g = celt_rsqrt_norm(t);

    xptr = X;

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

    {

       *xptr = EXTRACT16(PSHR32(MULT16_16(g, *xptr), k+1));

-      xptr += stride;

+      xptr++;

    }

-   return celt_sqrt(E);

+   /*return celt_sqrt(E);*/

 }

--- a/libcelt/vq.h

+++ b/libcelt/vq.h

@@ -62,6 +62,8 @@

  */

 void alg_unquant(celt_norm *X, int N, int K, int spread, int B, celt_norm *lowband, ec_dec *dec, celt_int32 *seed);

-celt_word16 renormalise_vector(celt_norm *X, celt_word16 value, int N, int stride);

+void renormalise_vector(celt_norm *X, int N);

+

+celt_word16 vector_norm(const celt_norm *X, int N);

 #endif /* VQ_H */