src/util/format_r11g11b10f.h

   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
  53 static 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
 101 static 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
 135 static 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
 183 static 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
 218 static 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
 225 static 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 */