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Synced fastlog.h with ardour1 updates.

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git-svn-id: svn://localhost/trunk/ardour2@16 d708f5d6-7413-0410-9779-e7cbd77b26cf
This commit is contained in:
Taybin Rutkin 2005-08-11 19:45:29 +00:00
parent 45866a0ab0
commit f9546e5c76
1 changed files with 4 additions and 2 deletions
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6
libs/pbd3/pbd/fastlog.h
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@ -11,14 +11,16 @@ static inline float fast_log2 (float val)
/* don't use reinterpret_cast<> because that prevents this /* don't use reinterpret_cast<> because that prevents this
from being used by pure C code (for example, GnomeCanvasItems) from being used by pure C code (for example, GnomeCanvasItems)
*/ */
int * const exp_ptr = (int *)(&val); union {float f; int i;} t;
t.f = val;
int * const exp_ptr = &t.i;
int x = *exp_ptr; int x = *exp_ptr;
const int log_2 = ((x >> 23) & 255) - 128; const int log_2 = ((x >> 23) & 255) - 128;
x &= ~(255 << 23); x &= ~(255 << 23);
x += 127 << 23; x += 127 << 23;
*exp_ptr = x; *exp_ptr = x;
val = ((-1.0f/3) * val + 2) * val - 2.0f/3; // (1) val = ((-1.0f/3) * t.f + 2) * t.f - 2.0f/3;
return (val + log_2); return (val + log_2);
} }