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More simplifications to the decoder renormalization loop.

This removes an XOR, an ADD, and an AND, and replaces them with
 an AND NOT in ec_dec_normalize().
Also, simplify the loop structure of ec_dec_cdf() and eliminate a
 CMOV.

--- a/libcelt/rangedec.c

+++ b/libcelt/rangedec.c

@@ -121,16 +121,13 @@

     int sym;

     _this->rng<<=EC_SYM_BITS;

     /*Use up the remaining bits from our last symbol.*/

-    sym=_this->rem<<EC_CODE_EXTRA&EC_SYM_MAX;

+    sym=_this->rem<<EC_CODE_EXTRA;

     /*Read the next value from the input.*/

     _this->rem=ec_dec_in(_this);

     /*Take the rest of the bits we need from this new symbol.*/

     sym|=_this->rem>>EC_SYM_BITS-EC_CODE_EXTRA;

-    _this->dif=(_this->dif<<EC_SYM_BITS)-sym+((1<<EC_SYM_BITS)-1)&EC_CODE_MASK;

-    /*dif must be smaller than EC_CODE_TOP.

-      This is equivalent to the slightly more readable:

-      if(_this->dif>=EC_CODE_TOP)_this->dif-=EC_CODE_TOP;*/

-    _this->dif^=_this->dif&EC_CODE_TOP;

+    /*And subtract them from dif, capped to be less than EC_CODE_TOP.*/

+    _this->dif=(_this->dif<<EC_SYM_BITS)+(EC_SYM_MAX&~sym)&EC_CODE_TOP-1;

   }

 }

@@ -225,20 +222,19 @@

   ec_uint32 s;

   ec_uint32 t;

   int       val;

-  r=_this->rng>>_ftb;

+  s=_this->rng;

   d=_this->dif;

-  _cdf++;

+  r=s>>_ftb;

   val=0;

-  t=0;

-  s=IMUL32(r,(1<<_ftb)-_cdf[0]);

-  while(d<s){

+  do{

     t=s;

     s=IMUL32(r,(1<<_ftb)-_cdf[++val]);

   }

+  while(d<s);

   _this->dif=d-s;

-  _this->rng=(val?t:_this->rng)-s;

+  _this->rng=t-s;

   ec_dec_normalize(_this);

-  return val;

+  return val-1;

 }

 ec_uint32 ec_dec_tell(ec_dec *_this,int _b){