u_format_r11g11b10f.h revision 028ce1cd0f5bb3e0169618cd572ac00968b8bd13 
1/*
2 * Copyright (C) 2011 Marek Olšák <maraeo@gmail.com>
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining a
5 * copy of this software and associated documentation files (the "Software"),
6 * to deal in the Software without restriction, including without limitation
7 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
8 * and/or sell copies of the Software, and to permit persons to whom the
9 * Software is furnished to do so, subject to the following conditions:
10 *
11 * The above copyright notice and this permission notice (including the next
12 * paragraph) shall be included in all copies or substantial portions of the
13 * Software.
14 *
15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
21 * DEALINGS IN THE SOFTWARE.
22 */
23
24/* Based on code from The OpenGL Programming Guide / 7th Edition, Appendix J.
25 * Available here: http://www.opengl-redbook.com/appendices/
26 * The algorithm in the book contains a bug though, which is fixed in the code
27 * below.
28 */
29
30#define UF11_EXPONENT_BIAS   15
31#define UF11_EXPONENT_BITS   0x1F
32#define UF11_EXPONENT_SHIFT  6
33#define UF11_MANTISSA_BITS   0x3F
34#define UF11_MANTISSA_SHIFT  (23 - UF11_EXPONENT_SHIFT)
35#define UF11_MAX_EXPONENT    (UF11_EXPONENT_BITS << UF11_EXPONENT_SHIFT)
36
37#define UF10_EXPONENT_BIAS   15
38#define UF10_EXPONENT_BITS   0x1F
39#define UF10_EXPONENT_SHIFT  5
40#define UF10_MANTISSA_BITS   0x1F
41#define UF10_MANTISSA_SHIFT  (23 - UF10_EXPONENT_SHIFT)
42#define UF10_MAX_EXPONENT    (UF10_EXPONENT_BITS << UF10_EXPONENT_SHIFT)
43
44#define F32_INFINITY         0x7f800000
45
46static INLINE unsigned f32_to_uf11(float val)
47{
48   union {
49      float f;
50      uint32_t ui;
51   } f32 = {val};
52
53   uint16_t uf11 = 0;
54
55   /* Decode little-endian 32-bit floating-point value */
56   int sign = (f32.ui >> 16) & 0x8000;
57   /* Map exponent to the range [-127,128] */
58   int exponent = ((f32.ui >> 23) & 0xff) - 127;
59   int mantissa = f32.ui & 0x007fffff;
60
61   if (sign) return 0;
62
63   if (exponent == 128) { /* Infinity or NaN */
64      uf11 = UF11_MAX_EXPONENT;
65      if (mantissa) uf11 |= (mantissa & UF11_MANTISSA_BITS);
66   }
67   else if (exponent > 15) { /* Overflow - flush to Infinity */
68      uf11 = UF11_MAX_EXPONENT;
69   }
70   else if (exponent > -15) { /* Representable value */
71      exponent += UF11_EXPONENT_BIAS;
72      mantissa >>= UF11_MANTISSA_SHIFT;
73      uf11 = exponent << UF11_EXPONENT_SHIFT | mantissa;
74   }
75
76   return uf11;
77}
78
79static INLINE float uf11_to_f32(uint16_t val)
80{
81   union {
82      float f;
83      uint32_t ui;
84   } f32;
85
86   int exponent = (val & 0x07c0) >> UF11_EXPONENT_SHIFT;
87   int mantissa = (val & 0x003f);
88
89   f32.f = 0.0;
90
91   if (exponent == 0) {
92      if (mantissa != 0) {
93         const float scale = 1.0 / (1 << 20);
94         f32.f = scale * mantissa;
95      }
96   }
97   else if (exponent == 31) {
98      f32.ui = F32_INFINITY | mantissa;
99   }
100   else {
101      float scale, decimal;
102      exponent -= 15;
103      if (exponent < 0) {
104         scale = 1.0 / (1 << -exponent);
105      }
106      else {
107         scale = 1 << exponent;
108      }
109      decimal = 1.0 + (float) mantissa / 64;
110      f32.f = scale * decimal;
111   }
112
113   return f32.f;
114}
115
116static INLINE unsigned f32_to_uf10(float val)
117{
118   union {
119      float f;
120      uint32_t ui;
121   } f32 = {val};
122
123   uint16_t uf10 = 0;
124
125   /* Decode little-endian 32-bit floating-point value */
126   int sign = (f32.ui >> 16) & 0x8000;
127   /* Map exponent to the range [-127,128] */
128   int exponent = ((f32.ui >> 23) & 0xff) - 127;
129   int mantissa = f32.ui & 0x007fffff;
130
131   if (sign) return 0;
132
133   if (exponent == 128) { /* Infinity or NaN */
134      uf10 = UF10_MAX_EXPONENT;
135      if (mantissa) uf10 |= (mantissa & UF10_MANTISSA_BITS);
136   }
137   else if (exponent > 15) { /* Overflow - flush to Infinity */
138      uf10 = UF10_MAX_EXPONENT;
139   }
140   else if (exponent > -15) { /* Representable value */
141      exponent += UF10_EXPONENT_BIAS;
142      mantissa >>= UF10_MANTISSA_SHIFT;
143      uf10 = exponent << UF10_EXPONENT_SHIFT | mantissa;
144   }
145
146   return uf10;
147}
148
149static INLINE float uf10_to_f32(uint16_t val)
150{
151   union {
152      float f;
153      uint32_t ui;
154   } f32;
155
156   int exponent = (val & 0x07c0) >> UF10_EXPONENT_SHIFT;
157   int mantissa = (val & 0x003f);
158
159   f32.f = 0.0;
160
161   if (exponent == 0) {
162      if (mantissa != 0) {
163         const float scale = 1.0 / (1 << 20);
164         f32.f = scale * mantissa;
165      }
166   }
167   else if (exponent == 31) {
168      f32.ui = F32_INFINITY | mantissa;
169   }
170   else {
171      float scale, decimal;
172      exponent -= 15;
173      if (exponent < 0) {
174         scale = 1.0 / (1 << -exponent);
175      }
176      else {
177         scale = 1 << exponent;
178      }
179      decimal = 1.0 + (float) mantissa / 32;
180      f32.f = scale * decimal;
181   }
182
183   return f32.f;
184}
185
186static INLINE unsigned float3_to_r11g11b10f(const float rgb[3])
187{
188   return ( f32_to_uf11(rgb[0]) & 0x7ff) |
189          ((f32_to_uf11(rgb[1]) & 0x7ff) << 11) |
190          ((f32_to_uf10(rgb[2]) & 0x3ff) << 22);
191}
192
193static INLINE void r11g11b10f_to_float3(unsigned rgb, float retval[3])
194{
195   retval[0] = uf11_to_f32( rgb        & 0x7ff);
196   retval[1] = uf11_to_f32((rgb >> 11) & 0x7ff);
197   retval[2] = uf10_to_f32((rgb >> 22) & 0x3ff);
198}
199