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#ifndef FORMAT_R11G11B10F_H
31#define FORMAT_R11G11B10F_H
32
33#include <stdint.h>
34
35#define UF11(e, m)           ((e << 6) | (m))
36#define UF11_EXPONENT_BIAS   15
37#define UF11_EXPONENT_BITS   0x1F
38#define UF11_EXPONENT_SHIFT  6
39#define UF11_MANTISSA_BITS   0x3F
40#define UF11_MANTISSA_SHIFT  (23 - UF11_EXPONENT_SHIFT)
41#define UF11_MAX_EXPONENT    (UF11_EXPONENT_BITS << UF11_EXPONENT_SHIFT)
42
43#define UF10(e, m)           ((e << 5) | (m))
44#define UF10_EXPONENT_BIAS   15
45#define UF10_EXPONENT_BITS   0x1F
46#define UF10_EXPONENT_SHIFT  5
47#define UF10_MANTISSA_BITS   0x1F
48#define UF10_MANTISSA_SHIFT  (23 - UF10_EXPONENT_SHIFT)
49#define UF10_MAX_EXPONENT    (UF10_EXPONENT_BITS << UF10_EXPONENT_SHIFT)
50
51#define F32_INFINITY         0x7f800000
52
53static inline uint32_t f32_to_uf11(float val)
54{
55   union {
56      float f;
57      uint32_t ui;
58   } f32 = {val};
59
60   uint16_t uf11 = 0;
61
62   /* Decode little-endian 32-bit floating-point value */
63   int sign = (f32.ui >> 16) & 0x8000;
64   /* Map exponent to the range [-127,128] */
65   int exponent = ((f32.ui >> 23) & 0xff) - 127;
66   int mantissa = f32.ui & 0x007fffff;
67
68   if (exponent == 128) { /* Infinity or NaN */
69      /* From the GL_EXT_packed_float spec:
70       *
71       *     "Additionally: negative infinity is converted to zero; positive
72       *      infinity is converted to positive infinity; and both positive and
73       *      negative NaN are converted to positive NaN."
74       */
75      uf11 = UF11_MAX_EXPONENT;
76      if (mantissa) {
77         uf11 |= 1; /* NaN */
78      } else {
79         if (sign)
80            uf11 = 0; /* 0.0 */
81      }
82   } else if (sign) {
83      return 0;
84   } else if (val > 65024.0f) {
85      /* From the GL_EXT_packed_float spec:
86       *
87       *     "Likewise, finite positive values greater than 65024 (the maximum
88       *      finite representable unsigned 11-bit floating-point value) are
89       *      converted to 65024."
90       */
91      uf11 = UF11(30, 63);
92   } else if (exponent > -15) { /* Representable value */
93      exponent += UF11_EXPONENT_BIAS;
94      mantissa >>= UF11_MANTISSA_SHIFT;
95      uf11 = exponent << UF11_EXPONENT_SHIFT | mantissa;
96   }
97
98   return uf11;
99}
100
101static inline float uf11_to_f32(uint16_t val)
102{
103   union {
104      float f;
105      uint32_t ui;
106   } f32;
107
108   int exponent = (val & 0x07c0) >> UF11_EXPONENT_SHIFT;
109   int mantissa = (val & 0x003f);
110
111   f32.f = 0.0;
112
113   if (exponent == 0) {
114      if (mantissa != 0) {
115         const float scale = 1.0 / (1 << 20);
116         f32.f = scale * mantissa;
117      }
118   } else if (exponent == 31) {
119      f32.ui = F32_INFINITY | mantissa;
120   } else {
121      float scale, decimal;
122      exponent -= 15;
123      if (exponent < 0) {
124         scale = 1.0f / (1 << -exponent);
125      } else {
126         scale = (float) (1 << exponent);
127      }
128      decimal = 1.0f + (float) mantissa / 64;
129      f32.f = scale * decimal;
130   }
131
132   return f32.f;
133}
134
135static inline uint32_t f32_to_uf10(float val)
136{
137   union {
138      float f;
139      uint32_t ui;
140   } f32 = {val};
141
142   uint16_t uf10 = 0;
143
144   /* Decode little-endian 32-bit floating-point value */
145   int sign = (f32.ui >> 16) & 0x8000;
146   /* Map exponent to the range [-127,128] */
147   int exponent = ((f32.ui >> 23) & 0xff) - 127;
148   int mantissa = f32.ui & 0x007fffff;
149
150   if (exponent == 128) {
151      /* From the GL_EXT_packed_float spec:
152       *
153       *     "Additionally: negative infinity is converted to zero; positive
154       *      infinity is converted to positive infinity; and both positive and
155       *      negative NaN are converted to positive NaN."
156       */
157      uf10 = UF10_MAX_EXPONENT;
158      if (mantissa) {
159         uf10 |= 1; /* NaN */
160      } else {
161         if (sign)
162            uf10 = 0; /* 0.0 */
163      }
164   } else if (sign) {
165      return 0;
166   } else if (val > 64512.0f) {
167      /* From the GL_EXT_packed_float spec:
168       *
169       *     "Likewise, finite positive values greater than 64512 (the maximum
170       *      finite representable unsigned 10-bit floating-point value) are
171       *      converted to 64512."
172       */
173      uf10 = UF10(30, 31);
174   } else if (exponent > -15) { /* Representable value */
175      exponent += UF10_EXPONENT_BIAS;
176      mantissa >>= UF10_MANTISSA_SHIFT;
177      uf10 = exponent << UF10_EXPONENT_SHIFT | mantissa;
178   }
179
180   return uf10;
181}
182
183static inline float uf10_to_f32(uint16_t val)
184{
185   union {
186      float f;
187      uint32_t ui;
188   } f32;
189
190   int exponent = (val & 0x03e0) >> UF10_EXPONENT_SHIFT;
191   int mantissa = (val & 0x001f);
192
193   f32.f = 0.0;
194
195   if (exponent == 0) {
196      if (mantissa != 0) {
197         const float scale = 1.0 / (1 << 19);
198         f32.f = scale * mantissa;
199      }
200   } else if (exponent == 31) {
201      f32.ui = F32_INFINITY | mantissa;
202   } else {
203      float scale, decimal;
204      exponent -= 15;
205      if (exponent < 0) {
206         scale = 1.0f / (1 << -exponent);
207      }
208      else {
209         scale = (float) (1 << exponent);
210      }
211      decimal = 1.0f + (float) mantissa / 32;
212      f32.f = scale * decimal;
213   }
214
215   return f32.f;
216}
217
218static inline uint32_t float3_to_r11g11b10f(const float rgb[3])
219{
220   return ( f32_to_uf11(rgb[0]) & 0x7ff) |
221          ((f32_to_uf11(rgb[1]) & 0x7ff) << 11) |
222          ((f32_to_uf10(rgb[2]) & 0x3ff) << 22);
223}
224
225static inline void r11g11b10f_to_float3(uint32_t rgb, float retval[3])
226{
227   retval[0] = uf11_to_f32( rgb        & 0x7ff);
228   retval[1] = uf11_to_f32((rgb >> 11) & 0x7ff);
229   retval[2] = uf10_to_f32((rgb >> 22) & 0x3ff);
230}
231
232#endif /* FORMAT_R11G11B10F_H */
233