41 lines
895 B
C
41 lines
895 B
C
/* Copyright unknown. Code by Laurent de Soras <laurent@ohmforce.com>.
|
|
*/
|
|
|
|
#ifndef __pbd_fastlog_h__
|
|
#define __pbd_fastlog_h__
|
|
|
|
#include <math.h> /* for HUGE_VAL */
|
|
|
|
static inline float fast_log2 (float val)
|
|
{
|
|
/* don't use reinterpret_cast<> because that prevents this
|
|
from being used by pure C code (for example, GnomeCanvasItems)
|
|
*/
|
|
union {float f; int i;} t;
|
|
t.f = val;
|
|
int * const exp_ptr = &t.i;
|
|
int x = *exp_ptr;
|
|
const int log_2 = ((x >> 23) & 255) - 128;
|
|
x &= ~(255 << 23);
|
|
x += 127 << 23;
|
|
*exp_ptr = x;
|
|
|
|
val = ((-1.0f/3) * t.f + 2) * t.f - 2.0f/3;
|
|
|
|
return (val + log_2);
|
|
}
|
|
|
|
static inline float fast_log (const float val)
|
|
{
|
|
return (fast_log2 (val) * 0.69314718f);
|
|
}
|
|
|
|
static inline float fast_log10 (const float val)
|
|
{
|
|
return fast_log2(val) / 3.312500f;
|
|
}
|
|
|
|
static inline float minus_infinity() { return -HUGE_VAL; }
|
|
|
|
#endif /* __pbd_fastlog_h__ */
|