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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