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6238bc0ece
especially now that we have a custom version of that code anyway. Moved the test code to tests/
101 lines
2.4 KiB
C
101 lines
2.4 KiB
C
#include "bitree.h"
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void ec_bitree_to_counts(unsigned *_this,int _sz,int _split){
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int p;
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int q;
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int s;
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for(p=_split;p>1;p=q){
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q=p>>1;
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for(s=p-1;s<_sz;s+=p)_this[s]-=_this[s-q];
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}
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}
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void ec_bitree_from_counts(unsigned *_this,int _sz){
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int p;
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int q;
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int s;
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for(q=1,p=2;p<=_sz;q=p,p=q<<1){
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for(s=p-1;s<_sz;s+=p)_this[s]+=_this[s-q];
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}
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}
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unsigned ec_bitree_get_cumul(const unsigned *_this,int _sym){
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unsigned ret;
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ret=0;
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while(_sym>0){
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ret+=_this[_sym-1];
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_sym&=_sym-1;
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}
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return ret;
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}
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unsigned ec_bitree_get_freq(const unsigned *_this,int _sym){
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unsigned ret;
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int p;
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ret=_this[_sym];
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p=_sym&_sym+1;
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while(_sym!=p){
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ret-=_this[_sym-1];
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_sym&=_sym-1;
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}
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return ret;
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}
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#if 0
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/*Fenwick's approach to re-scaling the counts.
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This tests to be twice as slow or more than the one below, even with inline
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functions enabled, and without loop vectorization (which would make Moffat's
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approach even faster).*/
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void ec_bitree_halve(unsigned *_this,int _sz,int _split){
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int i;
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for(i=_sz;i-->0;){
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ec_bitree_update(_this,_sz,i,-(int)(ec_bitree_get_freq(_this,i)>>1));
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}
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}
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#else
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/*Fenwick mentions that this approach is also possible, and this is what
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Moffat uses.
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Simply convert the tree into a simple array of counts, perform the halving,
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and then convert it back.*/
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void ec_bitree_halve(unsigned *_this,int _sz,int _split){
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int i;
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ec_bitree_to_counts(_this,_sz,_split);
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/*LOOP VECTORIZES.*/
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for(i=0;i<_sz;i++)_this[i]-=_this[i]>>1;
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ec_bitree_from_counts(_this,_sz);
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}
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#endif
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#if 0
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#include <stdio.h>
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/*Simple regression test code.
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Compile with bitrenc.c and bitrdec.c as well.*/
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static void ec_bitree_print(unsigned *_this,int _sz){
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int i;
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for(i=0;i<_sz;i++)printf("%3i%c",_this[i],i+1<_sz?' ':'\n');
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}
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int main(void){
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unsigned t[16]={0,8,4,9,2,10,5,11,1,12,6,13,3,14,7,15};
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int fl;
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int s;
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int i;
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ec_bitree_print(t,16);
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ec_bitree_from_counts(t,16);
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ec_bitree_print(t,16);
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for(i=0;i<=16;i++)printf("%3i%c",ec_bitree_get_cumul(t,i),i<16?' ':'\n');
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for(i=0;i<t[15];i++){
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s=ec_bitree_find_and_update(t,16,16,i,&fl,0);
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printf("%3i: %i %3i\n",i,s,fl);
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}
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for(i=0;i<16;i++){
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s=ec_bitree_find_and_update(t,16,ec_bitree_get_cumul(t,i),&fl,100);
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ec_bitree_to_counts(t,16,16);
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ec_bitree_print(t,16);
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ec_bitree_from_counts(t,16);
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ec_bitree_update(t,16,s,-100);
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}
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return 0;
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}
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#endif
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