1 /**************************************************************************
2 *
3 * Copyright 2010 Luca Barbieri
4 *
5 * Permission is hereby granted, free of charge, to any person obtaining
6 * a copy of this software and associated documentation files (the
7 * "Software"), to deal in the Software without restriction, including
8 * without limitation the rights to use, copy, modify, merge, publish,
9 * distribute, sublicense, and/or sell copies of the Software, and to
10 * permit persons to whom the Software is furnished to do so, subject to
11 * the following conditions:
12 *
13 * The above copyright notice and this permission notice (including the
14 * next paragraph) shall be included in all copies or substantial
15 * portions of the Software.
16 *
17 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
18 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
19 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
20 * IN NO EVENT SHALL THE COPYRIGHT OWNER(S) AND/OR ITS SUPPLIERS BE
21 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
22 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
23 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
24 *
25 **************************************************************************/
26
27
28 #ifndef U_HALF_H
29 #define U_HALF_H
30
31 #include "pipe/p_compiler.h"
32 #include "util/u_math.h"
33
34 #ifdef __cplusplus
35 extern "C" {
36 #endif
37
38 /*
39 * References for float <-> half conversions
40 *
41 * http://fgiesen.wordpress.com/2012/03/28/half-to-float-done-quic/
42 * https://gist.github.com/2156668
43 * https://gist.github.com/2144712
44 */
45
46 static inline uint16_t
util_float_to_half(float f)47 util_float_to_half(float f)
48 {
49 uint32_t sign_mask = 0x80000000;
50 uint32_t round_mask = ~0xfff;
51 uint32_t f32inf = 0xff << 23;
52 uint32_t f16inf = 0x1f << 23;
53 uint32_t sign;
54 union fi magic;
55 union fi f32;
56 uint16_t f16;
57
58 magic.ui = 0xf << 23;
59
60 f32.f = f;
61
62 /* Sign */
63 sign = f32.ui & sign_mask;
64 f32.ui ^= sign;
65
66 if (f32.ui == f32inf) {
67 /* Inf */
68 f16 = 0x7c00;
69 } else if (f32.ui > f32inf) {
70 /* NaN */
71 f16 = 0x7e00;
72 } else {
73 /* Number */
74 f32.ui &= round_mask;
75 f32.f *= magic.f;
76 f32.ui -= round_mask;
77 /*
78 * XXX: The magic mul relies on denorms being available, otherwise
79 * all f16 denorms get flushed to zero - hence when this is used
80 * for tgsi_exec in softpipe we won't get f16 denorms.
81 */
82 /*
83 * Clamp to max finite value if overflowed.
84 * OpenGL has completely undefined rounding behavior for float to
85 * half-float conversions, and this matches what is mandated for float
86 * to fp11/fp10, which recommend round-to-nearest-finite too.
87 * (d3d10 is deeply unhappy about flushing such values to infinity, and
88 * while it also mandates round-to-zero it doesn't care nearly as much
89 * about that.)
90 */
91 if (f32.ui > f16inf)
92 f32.ui = f16inf - 1;
93
94 f16 = f32.ui >> 13;
95 }
96
97 /* Sign */
98 f16 |= sign >> 16;
99
100 return f16;
101 }
102
103 static inline float
util_half_to_float(uint16_t f16)104 util_half_to_float(uint16_t f16)
105 {
106 union fi infnan;
107 union fi magic;
108 union fi f32;
109
110 infnan.ui = 0x8f << 23;
111 infnan.f = 65536.0f;
112 magic.ui = 0xef << 23;
113
114 /* Exponent / Mantissa */
115 f32.ui = (f16 & 0x7fff) << 13;
116
117 /* Adjust */
118 f32.f *= magic.f;
119 /* XXX: The magic mul relies on denorms being available */
120
121 /* Inf / NaN */
122 if (f32.f >= infnan.f)
123 f32.ui |= 0xff << 23;
124
125 /* Sign */
126 f32.ui |= (f16 & 0x8000) << 16;
127
128 return f32.f;
129 }
130
131 #ifdef __cplusplus
132 }
133 #endif
134
135 #endif /* U_HALF_H */
136
137