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Store the total budget of compute_allocation in BITRES units.

The margin of safety was supposed to be 1/8th bit, not 1 bit, and the
 bit we reserved to terminate skip signalling before was actually 8
 bits.
This patch updates the margin of safety to the correct value and
 accounts for the one bit (not 8) needed for skip signalling.
It also fixes the remainder calculation in the skip loop to work
 correctly when start>0.

--- a/libcelt/celt.c

+++ b/libcelt/celt.c

@@ -1119,8 +1119,8 @@

    ALLOC(pulses, st->mode->nbEBands, int);

    ALLOC(fine_priority, st->mode->nbEBands, int);

-   /* bits =   packet size    -    where we are   - safety */

-   bits = nbCompressedBytes*8 - ec_enc_tell(enc, 0) - 1;

+   /* bits =   packet size        -       where we are           - safety - skip signalling*/

+   bits = (nbCompressedBytes*8<<BITRES) - ec_enc_tell(enc, BITRES) - 1    - (1<<BITRES);

    codedBands = compute_allocation(st->mode, st->start, st->end, offsets,

          alloc_trim, bits, pulses, fine_quant, fine_priority, C, LM, enc, 1, st->lastCodedBands);

    st->lastCodedBands = codedBands;

@@ -1856,7 +1856,7 @@

       intensity = ec_dec_uint(dec, 1+st->end-st->start);

    }

-   bits = len*8 - ec_dec_tell(dec, 0) - 1;

+   bits = (len*8<<BITRES) - ec_dec_tell(dec, BITRES) - 1 - (1<<BITRES);

    codedBands = compute_allocation(st->mode, st->start, st->end, offsets,

          alloc_trim, bits, pulses, fine_quant, fine_priority, C, LM, dec, 0, 0);

--- a/libcelt/rate.c

+++ b/libcelt/rate.c

@@ -178,7 +178,7 @@

                psum += alloc_floor;

          }

       }

-      if (psum > (total<<BITRES))

+      if (psum > total)

          hi = mid;

       else

          lo = mid;

@@ -214,10 +214,10 @@

       int rem;

       /*Figure out how many left-over bits we would be adding to this band.

         This can include bits we've stolen back from higher, skipped bands.*/

-      left = (total<<BITRES)-psum;

+      left = total-psum;

       percoeff = left/(m->eBands[codedBands]-m->eBands[start]);

       left -= (m->eBands[codedBands]-m->eBands[start])*percoeff;

-      rem = IMAX(left-m->eBands[j],0);

+      rem = IMAX(left-(m->eBands[j]-m->eBands[start]),0);

       band_width = m->eBands[codedBands]-m->eBands[j];

       band_bits = bits[j] + percoeff*band_width + rem;

       /*Only code a skip decision if we're above the threshold for this band.

@@ -379,7 +379,7 @@

          /*printf ("%d ", bits[j]);*/

       }

       /*printf ("\n");*/

-      if (psum > (total<<BITRES))

+      if (psum > total)

          hi = mid;

       else

          lo = mid;