shithub: opus

ref: 46f3700e55953c3c279ea5d94784ed063fab0466
dir: /libcelt/entcode.c/

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

#include "entcode.h"







int ec_ilog(ec_uint32 _v){
#if defined(EC_CLZ)
  return EC_CLZ0-EC_CLZ(_v);
#else
  /*On a Pentium M, this branchless version tested as the fastest on
     1,000,000,000 random 32-bit integers, edging out a similar version with
     branches, and a 256-entry LUT version.*/
  int ret;
  int m;
  ret=!!_v;
  m=!!(_v&0xFFFF0000)<<4;
  _v>>=m;
  ret|=m;
  m=!!(_v&0xFF00)<<3;
  _v>>=m;
  ret|=m;
  m=!!(_v&0xF0)<<2;
  _v>>=m;
  ret|=m;
  m=!!(_v&0xC)<<1;
  _v>>=m;
  ret|=m;
  ret+=!!(_v&0x2);
  return ret;
#endif
}

int ec_ilog64(ec_uint64 _v){
#if defined(EC_CLZ64)
  return EC_CLZ64_0-EC_CLZ64(_v);
#else
  ec_uint32 v;
  int       ret;
  int       m;
  ret=!!_v;
  m=!!(_v&((ec_uint64)0xFFFFFFFF)<<32)<<5;
  v=(ec_uint32)(_v>>m);
  ret|=m;
  m=!!(v&0xFFFF0000)<<4;
  v>>=m;
  ret|=m;
  m=!!(v&0xFF00)<<3;
  v>>=m;
  ret|=m;
  m=!!(v&0xF0)<<2;
  v>>=m;
  ret|=m;
  m=!!(v&0xC)<<1;
  v>>=m;
  ret|=m;
  ret+=!!(v&0x2);
  return ret;
#endif
}