src/uobject/primitives.c

   1 /*
   2  *  upkg: tool for manipulating Unreal Tournament packages.
   3  *  Copyright © 2012, 2020 Nick Bowler
   4  *
   5  *  This program is free software: you can redistribute it and/or modify
   6  *  it under the terms of the GNU General Public License as published by
   7  *  the Free Software Foundation, either version 3 of the License, or
   8  *  (at your option) any later version.
   9  *
  10  *  This program is distributed in the hope that it will be useful,
  11  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  *  GNU General Public License for more details.
  14  *
  15  *  You should have received a copy of the GNU General Public License
  16  *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17  */
  18
  19 #include <config.h>
  20 #include <math.h>
  21
  22 #include <uobject/uobject.h>
  23 #include "pack.h"
  24
  25 /*
  26  * Deserialize an IEEE 754 binary32 value in "little endian" (for whatever
  27  * that term is worth in this context).  That is, when interpreted as a little
  28  * endian 32-bit unsigned integer: bit 31 is the sign, bits 30-23 are the
  29  * (biased) exponent, and bits 22-0 are the encoded part of the significand.
  30  *
  31  * The implementation is designed to be agnostic of the platform's actual
  32  * float type, but the conversion may be lossy if "float" is not itself a
  33  * binary32 format.  NaN payloads are not preserved.
  34  */
  35 float u_unpack_binary32_le(const unsigned char *buf)
  36 {
  37         unsigned long raw;
  38         long significand;
  39         int exponent;
  40         float result;
  41
  42         raw = unpack_32_le(buf);
  43         exponent = (raw & 0x7f800000) >> 23;
  44         significand = (raw & 0x007fffff) >> 0;
  45
  46         switch (exponent) {
  47         case 255:
  48                 result = significand ? NAN : INFINITY;
  49                 break;
  50         default:
  51                 significand |= 0x00800000;
  52                 /* fall through */
  53         case 0:
  54                 result = ldexpf(significand, exponent-126-24);
  55         }
  56
  57         return copysignf(result, raw & 0x80000000 ? -1 : 1);
  58 }