source/lib/bits.cpp

   1 /* Copyright (c) 2010 Wildfire Games
   2  *
   3  * Permission is hereby granted, free of charge, to any person obtaining
   4  * a copy of this software and associated documentation files (the
   5  * "Software"), to deal in the Software without restriction, including
   6  * without limitation the rights to use, copy, modify, merge, publish,
   7  * distribute, sublicense, and/or sell copies of the Software, and to
   8  * permit persons to whom the Software is furnished to do so, subject to
   9  * the following conditions:
  10  *
  11  * The above copyright notice and this permission notice shall be included
  12  * in all copies or substantial portions of the Software.
  13  *
  14  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  15  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  16  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
  17  * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
  18  * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
  19  * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
  20  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  21  */
  22
  23 /*
  24  * bit-twiddling.
  25  */
  26
  27 #include "precompiled.h"
  28 #include "lib/bits.h"
  29
  30 static inline u32 get_float_bits(const float x)
  31 {
  32         u32 ret;
  33         memcpy(&ret, &x, 4);
  34         return ret;
  35 }
  36
  37 int floor_log2(const float x)
  38 {
  39         const u32 i = get_float_bits(x);
  40         const u32 biased_exp = (i >> 23) & 0xFF;
  41         return (int)biased_exp - 127;
  42 }