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Bit allocation

Also convert the stereo split code to use log(N)/2 as the bit allocation
offset

--- a/libcelt/bands.c

+++ b/libcelt/bands.c

@@ -598,11 +598,11 @@

       int qalloc;

       celt_word16 mid, side;

       int offset, N2;

-      offset = m->logN[i]+(LM<<BITRES)-QTHETA_OFFSET;

+      offset = ((m->logN[i]+(LM<<BITRES))>>1)-QTHETA_OFFSET;

       /* Decide on the resolution to give to the split parameter theta */

       N2 = 2*N-1;

-      if (stereo && N>2)

+      if (stereo && N==2)

          N2--;

       qb = (b+N2*offset)/(N2<<BITRES);

       if (qb > (b>>(BITRES+1))-1)

@@ -627,7 +627,7 @@

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

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

-            /* theta is the atan() of the ration between the (normalized)

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

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

                mid and side because we know that 1) they have unit norm and

                2) they are orthogonal. */

--- a/libcelt/rate.c

+++ b/libcelt/rate.c

@@ -173,8 +173,8 @@

       if (N==1)

          ebits[j] = (bits[j]/C >> BITRES)-1;

-      if (ebits[j] < 1)

-         ebits[j] = 1;

+      if (ebits[j] < C)

+         ebits[j] = C;

       /* Make sure not to bust */

       if (C*ebits[j] > (bits[j]>>BITRES))

          ebits[j] = bits[j]/C >> BITRES;

--- a/libcelt/rate.h

+++ b/libcelt/rate.h

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

 #define BITRES 3

 #define FINE_OFFSET 14

-#define QTHETA_OFFSET 18

+#define QTHETA_OFFSET (-2)

 #define BITOVERFLOW 30000