YODA/Utils/fastlog.h

0001 /*=====================================================================*
0002  *                   Copyright (C) 2011 Paul Mineiro                   *
0003  * All rights reserved.                                                *
0004  *                                                                     *
0005  * Redistribution and use in source and binary forms, with             *
0006  * or without modification, are permitted provided that the            *
0007  * following conditions are met:                                       *
0008  *                                                                     *
0009  *     * Redistributions of source code must retain the                *
0010  *     above copyright notice, this list of conditions and             *
0011  *     the following disclaimer.                                       *
0012  *                                                                     *
0013  *     * Redistributions in binary form must reproduce the             *
0014  *     above copyright notice, this list of conditions and             *
0015  *     the following disclaimer in the documentation and/or            *
0016  *     other materials provided with the distribution.                 *
0017  *                                                                     *
0018  *     * Neither the name of Paul Mineiro nor the names                *
0019  *     of other contributors may be used to endorse or promote         *
0020  *     products derived from this software without specific            *
0021  *     prior written permission.                                       *
0022  *                                                                     *
0023  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND              *
0024  * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,         *
0025  * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES               *
0026  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE             *
0027  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER               *
0028  * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,                 *
0029  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES            *
0030  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE           *
0031  * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR                *
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0035  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE             *
0036  * POSSIBILITY OF SUCH DAMAGE.                                         *
0037  *                                                                     *
0038  * Contact: Paul Mineiro <paul@mineiro.com>                            *
0039  *=====================================================================*/
0040
0041 #ifndef __FAST_LOG_H_
0042 #define __FAST_LOG_H_
0043
0044 #include <stdint.h>
0045
0046 namespace YODA {
0047   namespace Utils {
0048     static inline float
0049       fastlog2 (float x)
0050       {
0051         union { float f; uint32_t i; } vx = { x };
0052         union { uint32_t i; float f; } mx = { (vx.i & 0x007FFFFF) | 0x3f000000 };
0053         float y = vx.i;
0054         y *= 1.1920928955078125e-7f;
0055
0056         return y - 124.22551499f
0057           - 1.498030302f * mx.f
0058           - 1.72587999f / (0.3520887068f + mx.f);
0059       }
0060
0061     static inline float
0062       fasterlog2 (float x)
0063       {
0064         union { float f; uint32_t i; } vx = { x };
0065         float y = vx.i;
0066         y *= 1.1920928955078125e-7f;
0067         return y - 126.94269504f;
0068       }
0069   }
0070 }
0071 #endif // __FAST_LOG_H_