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//=========================================================
// MusE
// Linux Music Editor
// $Id: ./muse/fastlog.h $
//
// Copyright (C) 1999-2011 by Werner Schweer and others
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; version 2 of
// the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
//
//=========================================================
/* Copyright unknown. Code by Laurent de Soras <laurent@ohmforce.com>.
*/
#ifndef __pbd_fastlog_h__
#define __pbd_fastlog_h__
#include <math.h> /* for HUGE_VAL */
namespace MusECore {
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; }
} // namespace MusECore
#endif /* __pbd_fastlog_h__ */
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