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Use __builtin_clz instead of default implementation of fixnormz on GCC

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The library contains architecture specific versions of the clz functions
for arm and mips, but the fallback C version for other architectures is
pretty slow.

By using __builtin_clz on GCC (available since GCC 3.4), we get a
significant (20-40 %) speedup of the total running time on x86.

Speed difference: 5.1 s instead of 8.6 s for AAC-LC 128 kbit/s and
3.8 s instead of 4.9 s for HE-AACv2 32 kbit/s, on an i7.
This commit is contained in:
Jakub Stachowski 2012-08-11 16:31:02 +02:00 committed by Martin Storsjo
parent 6999980d67
commit e036dbc8eb
1 changed files with 12 additions and 0 deletions
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12
libFDK/include/clz.h
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@ -115,6 +115,11 @@ inline INT fixnormz_S (SHORT a)
{
return fixnormz_D((INT)(a));
}
#elif defined(__GNUC__)
inline INT fixnormz_S (SHORT a)
{
return a ? __builtin_clz(a) : 16;
}
#else
inline INT fixnormz_S (SHORT a)
{
@ -131,6 +136,12 @@ inline INT fixnormz_S (SHORT a)
#endif
#if !defined(FUNCTION_fixnormz_D)
#if defined(__GNUC__)
inline INT fixnormz_D (LONG a)
{
return a ? __builtin_clz(a) : 32;
}
#else
inline INT fixnormz_D (LONG a)
{
INT leadingBits = 0;
@ -143,6 +154,7 @@ inline INT fixnormz_D (LONG a)
return (leadingBits);
}
#endif
#endif
/*****************************************************************************