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    }
  90    else if (exponent > -15) { /* Representable value */
  91       exponent += UF11_EXPONENT_BIAS;
  92       mantissa >>= UF11_MANTISSA_SHIFT;
  93       uf11 = exponent << UF11_EXPONENT_SHIFT | mantissa;
  94    }
  95
  96    return uf11;
  97 }
  98
  99 static inline float uf11_to_f32(uint16_t val)
 100 {
 101    union {
 102       float f;
 103       uint32_t ui;
 104    } f32;
 105
 106    int exponent = (val & 0x07c0) >> UF11_EXPONENT_SHIFT;
 107    int mantissa = (val & 0x003f);
 108
 109    f32.f = 0.0;
 110
 111    if (exponent == 0) {
 112       if (mantissa != 0) {
 113          const float scale = 1.0 / (1 << 20);
 114          f32.f = scale * mantissa;
 115       }
 116    }
 117    else if (exponent == 31) {
 118       f32.ui = F32_INFINITY | mantissa;
 119    }
 120    else {
 121       float scale, decimal;
 122       exponent -= 15;
 123       if (exponent < 0) {
 124          scale = 1.0f / (1 << -exponent);
 125       }
 126       else {
 127          scale = (float) (1 << exponent);
 128       }
 129       decimal = 1.0f + (float) mantissa / 64;
 130       f32.f = scale * decimal;
 131    }
 132
 133    return f32.f;
 134 }
 135
 136 static inline uint32_t f32_to_uf10(float val)
 137 {
 138    union {
 139       float f;
 140       uint32_t ui;
 141    } f32 = {val};
 142
 143    uint16_t uf10 = 0;
 144
 145    /* Decode little-endian 32-bit floating-point value */
 146    int sign = (f32.ui >> 16) & 0x8000;
 147    /* Map exponent to the range [-127,128] */
 148    int exponent = ((f32.ui >> 23) & 0xff) - 127;
 149    int mantissa = f32.ui & 0x007fffff;
 150
 151    if (exponent == 128) {
 152       /* From the GL_EXT_packed_float spec:
 153        *
 154        *     "Additionally: negative infinity is converted to zero; positive
 155        *      infinity is converted to positive infinity; and both positive and
 156        *      negative NaN are converted to positive NaN."
 157        */
 158       uf10 = UF10_MAX_EXPONENT;
 159       if (mantissa) {
 160          uf10 |= 1; /* NaN */
 161       } else {
 162          if (sign)
 163             uf10 = 0; /* 0.0 */
 164       }
 165    } else if (sign) {
 166       return 0;
 167    } else if (val > 64512.0f) {
 168       /* From the GL_EXT_packed_float spec:
 169        *
 170        *     "Likewise, finite positive values greater than 64512 (the maximum
 171        *      finite representable unsigned 10-bit floating-point value) are
 172        *      converted to 64512."
 173        */
 174       uf10 = UF10(30, 31);
 175    }
 176    else if (exponent > -15) { /* Representable value */
 177       exponent += UF10_EXPONENT_BIAS;
 178       mantissa >>= UF10_MANTISSA_SHIFT;
 179       uf10 = exponent << UF10_EXPONENT_SHIFT | mantissa;
 180    }
 181
 182    return uf10;
 183 }
 184
 185 static inline float uf10_to_f32(uint16_t val)
 186 {
 187    union {
 188       float f;
 189       uint32_t ui;
 190    } f32;
 191
 192    int exponent = (val & 0x03e0) >> UF10_EXPONENT_SHIFT;
 193    int mantissa = (val & 0x001f);
 194
 195    f32.f = 0.0;
 196
 197    if (exponent == 0) {
 198       if (mantissa != 0) {
 199          const float scale = 1.0 / (1 << 20);
 200          f32.f = scale * mantissa;
 201       }
 202    }
 203    else if (exponent == 31) {
 204       f32.ui = F32_INFINITY | mantissa;
 205    }
 206    else {
 207       float scale, decimal;
 208       exponent -= 15;
 209       if (exponent < 0) {
 210          scale = 1.0f / (1 << -exponent);
 211       }
 212       else {
 213          scale = (float) (1 << exponent);
 214       }
 215       decimal = 1.0f + (float) mantissa / 32;
 216       f32.f = scale * decimal;
 217    }
 218
 219    return f32.f;
 220 }
 221
 222 static inline uint32_t float3_to_r11g11b10f(const float rgb[3])
 223 {
 224    return ( f32_to_uf11(rgb[0]) & 0x7ff) |
 225           ((f32_to_uf11(rgb[1]) & 0x7ff) << 11) |
 226           ((f32_to_uf10(rgb[2]) & 0x3ff) << 22);
 227 }
 228
 229 static inline void r11g11b10f_to_float3(uint32_t rgb, float retval[3])
 230 {
 231    retval[0] = uf11_to_f32( rgb        & 0x7ff);
 232    retval[1] = uf11_to_f32((rgb >> 11) & 0x7ff);
 233    retval[2] = uf10_to_f32((rgb >> 22) & 0x3ff);
 234 }