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