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bitmath.h : Fixes for FLAC__bitmath_ilog2_wide().

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Existing version had a number of problems:
1) it didn't compile with MSVS
2) it returned correct results only when compiles with GNUC
3) it mentioned LGPL which isn't good for a BSD-licensed library

LGPL -> BSD issue documented here:
http://lists.xiph.org/pipermail/flac-dev/2013-September/004356.html

Patch-from: lvqcl <lvqcl.mail@gmail.com>
This commit is contained in:
Erik de Castro Lopo
2014-02-02 10:42:17 +11:00
parent 96011ffa60
commit 71c9555366
1 changed files with 23 additions and 22 deletions
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45
src/libFLAC/include/private/bitmath.h
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@@ -142,33 +142,34 @@ static inline unsigned FLAC__bitmath_ilog2_wide(FLAC__uint64 v)
return 0;
#if defined(__GNUC__) && (__GNUC__ >= 4 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 4))
return sizeof(FLAC__uint64) * CHAR_BIT - 1 - __builtin_clzll(v);
/* Sorry, only supported in win64/Itanium.. */
/* Sorry, only supported in win64/Itanium.. and both have fast FPU which makes integer-only encoder pointless */
#elif (defined(_MSC_VER) && (_MSC_VER >= 1400)) && (defined(_M_IA64) || defined(_WIN64))
FLAC__uint64 idx;
_BitScanReverse64(&idx, v);
return idx ^ 63U;
{
unsigned long idx;
_BitScanReverse64(&idx, v);
return idx;
}
#else
/* Brain-damaged compilers will use the fastest possible way that is,
de Bruijn sequences (http://supertech.csail.mit.edu/papers/debruijn.pdf)
(C) Timothy B. Terriberry (tterribe@xiph.org) 2001-2009 LGPL (v2 or later).
(C) Timothy B. Terriberry (tterribe@xiph.org) 2001-2009 CC0 (Public domain).
*/
static const unsigned char DEBRUIJN_IDX64[64]={
0, 1, 2, 7, 3,13, 8,19, 4,25,14,28, 9,34,20,40,
5,17,26,38,15,46,29,48,10,31,35,54,21,50,41,57,
63, 6,12,18,24,27,33,39,16,37,45,47,30,53,49,56,
62,11,23,32,36,44,52,55,61,22,43,51,60,42,59,58
};
int ret;
ret= v>0;
v|= v>>1;
v|= v>>2;
v|= v>>4;
v|= v>>8;
v|= v>>16;
v|= v>>32;
v= (v>>1)+1;
ret+=DEBRUIJN_IDX64[v*0x218A392CD3D5DBF>>58&0x3F];
return ret;
{
static const unsigned char DEBRUIJN_IDX64[64]={
0, 1, 2, 7, 3,13, 8,19, 4,25,14,28, 9,34,20,40,
5,17,26,38,15,46,29,48,10,31,35,54,21,50,41,57,
63, 6,12,18,24,27,33,39,16,37,45,47,30,53,49,56,
62,11,23,32,36,44,52,55,61,22,43,51,60,42,59,58
};
v|= v>>1;
v|= v>>2;
v|= v>>4;
v|= v>>8;
v|= v>>16;
v|= v>>32;
v= (v>>1)+1;
return DEBRUIJN_IDX64[v*0x218A392CD3D5DBF>>58&0x3F];
}
#endif
}
#endif