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 #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
  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
  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
 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
 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 << 20);
 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
 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
 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 }