43 lines
1,001 B
C
43 lines
1,001 B
C
/* Copyright unknown. Code by Laurent de Soras <laurent@ohmforce.com>.
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* This file is licensed under the WTFPL v2 license.
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* http://www.wtfpl.net/about/
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*/
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#ifndef __FASTLOG_H__
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#define __FASTLOG_H__
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#include <math.h> /* for HUGE_VAL */
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static inline float fast_log2(float val)
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{
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/* don't use reinterpret_cast<> because that prevents this
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from being used by pure C code (for example, GnomeCanvasItems)
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*/
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union {
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float f;
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int i;
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} t;
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t.f = val;
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int* const exp_ptr = &t.i;
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int x = *exp_ptr;
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const int log_2 = ((x >> 23) & 255) - 128;
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x &= ~(255 << 23);
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x += 127 << 23;
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*exp_ptr = x;
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val = ((-1.0f / 3) * t.f + 2) * t.f - 2.0f / 3;
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return val + log_2;
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}
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static inline float fast_log(const float val)
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{
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return fast_log2(val) * 0.69314718f;
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}
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static inline float fast_log10(const float val)
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{
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return fast_log2(val) / 3.312500f;
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}
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static inline float minus_infinity() { return -HUGE_VAL; }
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#endif
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