summaryrefslogtreecommitdiffstats
path: root/src/gallium/auxiliary/util/u_half.h
blob: d340b9a7aefcc2e302b42cec96e64293e624bc8b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
/**************************************************************************
 *
 * Copyright 2010 Luca Barbieri
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice (including the
 * next paragraph) shall be included in all copies or substantial
 * portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE COPYRIGHT OWNER(S) AND/OR ITS SUPPLIERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 **************************************************************************/


#ifndef U_HALF_H
#define U_HALF_H

#include "pipe/p_compiler.h"
#include "util/u_math.h"

#ifdef __cplusplus
extern "C" {
#endif

/*
 * References for float <-> half conversions
 *
 *  http://fgiesen.wordpress.com/2012/03/28/half-to-float-done-quic/
 *  https://gist.github.com/2156668
 *  https://gist.github.com/2144712
 */

static INLINE uint16_t
util_float_to_half(float f)
{
   uint32_t sign_mask  = 0x80000000;
   uint32_t round_mask = ~0xfff;
   uint32_t f32inf = 0xff << 23;
   uint32_t f16inf = 0x1f << 23;
   uint32_t sign;
   union fi magic;
   union fi f32;
   uint16_t f16;

   magic.ui = 0xf << 23;

   f32.f = f;

   /* Sign */
   sign = f32.ui & sign_mask;
   f32.ui ^= sign;

   if (f32.ui == f32inf) {
      /* Inf */
      f16 = 0x7c00;
   } else if (f32.ui > f32inf) {
      /* NaN */
      f16 = 0x7e00;
   } else {
      /* Number */
      f32.ui &= round_mask;
      f32.f  *= magic.f;
      f32.ui -= round_mask;

      /*
       * Clamp to max finite value if overflowed.
       * OpenGL has completely undefined rounding behavior for float to
       * half-float conversions, and this matches what is mandated for float
       * to fp11/fp10, which recommend round-to-nearest-finite too.
       * (d3d10 is deeply unhappy about flushing such values to infinity, and
       * while it also mandates round-to-zero it doesn't care nearly as much
       * about that.)
       */
      if (f32.ui > f16inf)
         f32.ui = f16inf - 1;

      f16 = f32.ui >> 13;
   }

   /* Sign */
   f16 |= sign >> 16;

   return f16;
}

static INLINE float
util_half_to_float(uint16_t f16)
{
   union fi infnan;
   union fi magic;
   union fi f32;

   infnan.ui = 0x8f << 23;
   infnan.f = 65536.0f;
   magic.ui  = 0xef << 23;

   /* Exponent / Mantissa */
   f32.ui = (f16 & 0x7fff) << 13;

   /* Adjust */
   f32.f *= magic.f;

   /* Inf / NaN */
   if (f32.f >= infnan.f)
      f32.ui |= 0xff << 23;

   /* Sign */
   f32.ui |= (f16 & 0x8000) << 16;

   return f32.f;
}

#ifdef __cplusplus
}
#endif

#endif /* U_HALF_H */