71 lines
2.2 KiB
C
71 lines
2.2 KiB
C
|
/* (C) 2001-2008 Timothy B. Terriberry
|
||
|
|
*/
|
||
|
|
/*
|
||
|
|
Redistribution and use in source and binary forms, with or without
|
||
|
|
modification, are permitted provided that the following conditions
|
||
|
|
are met:
|
||
|
|
|
||
|
|
- Redistributions of source code must retain the above copyright
|
||
|
|
notice, this list of conditions and the following disclaimer.
|
||
|
|
|
||
|
|
- Redistributions in binary form must reproduce the above copyright
|
||
|
|
notice, this list of conditions and the following disclaimer in the
|
||
|
|
documentation and/or other materials provided with the distribution.
|
||
|
|
|
||
|
|
- Neither the name of the Xiph.org Foundation nor the names of its
|
||
|
|
contributors may be used to endorse or promote products derived from
|
||
|
|
this software without specific prior written permission.
|
||
|
|
|
||
|
|
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
|
||
|
|
``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
|
||
|
|
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
|
||
|
|
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR
|
||
|
|
CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
|
||
|
|
EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
|
||
|
|
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
|
||
|
|
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
|
||
|
|
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
|
||
|
|
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
|
||
|
|
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
|
||
|
|
*/
|
||
|
|
|
||
|
|
#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
|
||
|
|
}
|
||
|
|
|