shithub: opus

ref: 2f5ccf60b11de248942cd0ac535d3b8e55f5898b
dir: /libcelt/bitree.c/

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "bitree.h"

void ec_bitree_to_counts(unsigned *_this,int _sz,int _split){
  int p;
  int q;
  int s;
  for(p=_split;p>1;p=q){
    q=p>>1;
    for(s=p-1;s<_sz;s+=p)_this[s]-=_this[s-q];
  }
}

void ec_bitree_from_counts(unsigned *_this,int _sz){
  int p;
  int q;
  int s;
  for(q=1,p=2;p<=_sz;q=p,p=q<<1){
    for(s=p-1;s<_sz;s+=p)_this[s]+=_this[s-q];
  }
}

unsigned ec_bitree_get_cumul(const unsigned *_this,int _sym){
  unsigned ret;
  ret=0;
  while(_sym>0){
    ret+=_this[_sym-1];
    _sym&=_sym-1;
  }
  return ret;
}

unsigned ec_bitree_get_freq(const unsigned *_this,int _sym){
  unsigned ret;
  int      p;
  ret=_this[_sym];
  p=_sym&_sym+1;
  while(_sym!=p){
    ret-=_this[_sym-1];
    _sym&=_sym-1;
  }
  return ret;
}

#if 0
/*Fenwick's approach to re-scaling the counts.
  This tests to be twice as slow or more than the one below, even with inline
   functions enabled, and without loop vectorization (which would make Moffat's
   approach even faster).*/
void ec_bitree_halve(unsigned *_this,int _sz,int _split){
  int i;
  for(i=_sz;i-->0;){
    ec_bitree_update(_this,_sz,i,-(int)(ec_bitree_get_freq(_this,i)>>1));
  }
}
#else
/*Fenwick mentions that this approach is also possible, and this is what
   Moffat uses.
  Simply convert the tree into a simple array of counts, perform the halving,
   and then convert it back.*/
void ec_bitree_halve(unsigned *_this,int _sz,int _split){
  int i;
  ec_bitree_to_counts(_this,_sz,_split);
  /*LOOP VECTORIZES.*/
  for(i=0;i<_sz;i++)_this[i]-=_this[i]>>1;
  ec_bitree_from_counts(_this,_sz);
}
#endif