tests/util/rgb9e5.c

   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 /* Copied from EXT_texture_shared_exponent */
  25
  26 #include "rgb9e5.h"
  27 #include <math.h>
  28 #include <assert.h>
  29
  30 #define MAX2( A, B )   ( (A)>(B) ? (A) : (B) )
  31
  32 /* XXX assuming little endian */
  33
  34 #define RGB9E5_EXPONENT_BITS          5
  35 #define RGB9E5_MANTISSA_BITS          9
  36 #define RGB9E5_EXP_BIAS               15
  37 #define RGB9E5_MAX_VALID_BIASED_EXP   31
  38
  39 #define MAX_RGB9E5_EXP               (RGB9E5_MAX_VALID_BIASED_EXP - RGB9E5_EXP_BIAS)
  40 #define RGB9E5_MANTISSA_VALUES       (1<<RGB9E5_MANTISSA_BITS)
  41 #define MAX_RGB9E5_MANTISSA          (RGB9E5_MANTISSA_VALUES-1)
  42 #define MAX_RGB9E5                   (((float)MAX_RGB9E5_MANTISSA)/RGB9E5_MANTISSA_VALUES * (1<<MAX_RGB9E5_EXP))
  43 #define EPSILON_RGB9E5               ((1.0/RGB9E5_MANTISSA_VALUES) / (1<<RGB9E5_EXP_BIAS))
  44
  45 typedef struct {
  46 #ifdef __BIG_ENDIAN__
  47    unsigned int negative:1;
  48    unsigned int biasedexponent:8;
  49    unsigned int mantissa:23;
  50 #else
  51    unsigned int mantissa:23;
  52    unsigned int biasedexponent:8;
  53    unsigned int negative:1;
  54 #endif
  55 } BitsOfIEEE754;
  56
  57 typedef union {
  58    unsigned int raw;
  59    float value;
  60    BitsOfIEEE754 field;
  61 } float754;
  62
  63 typedef struct {
  64 #ifdef __BIG_ENDIAN__
  65    unsigned int biasedexponent:RGB9E5_EXPONENT_BITS;
  66    unsigned int b:RGB9E5_MANTISSA_BITS;
  67    unsigned int g:RGB9E5_MANTISSA_BITS;
  68    unsigned int r:RGB9E5_MANTISSA_BITS;
  69 #else
  70    unsigned int r:RGB9E5_MANTISSA_BITS;
  71    unsigned int g:RGB9E5_MANTISSA_BITS;
  72    unsigned int b:RGB9E5_MANTISSA_BITS;
  73    unsigned int biasedexponent:RGB9E5_EXPONENT_BITS;
  74 #endif
  75 } BitsOfRGB9E5;
  76
  77 typedef union {
  78    unsigned int raw;
  79    BitsOfRGB9E5 field;
  80 } rgb9e5;
  81
  82 static float ClampRange_for_rgb9e5(float x)
  83 {
  84    if (x > 0.0) {
  85       if (x >= MAX_RGB9E5) {
  86          return MAX_RGB9E5;
  87       } else {
  88          return x;
  89       }
  90    } else {
  91       /* NaN gets here too since comparisons with NaN always fail! */
  92       return 0.0;
  93    }
  94 }
  95
  96 static float MaxOf3(float x, float y, float z)
  97 {
  98    if (x > y) {
  99       return MAX2(x, z);
 100    } else {
 101       return MAX2(y, z);
 102    }
 103 }
 104
 105 /* Ok, FloorLog2 is not correct for the denorm and zero values, but we
 106    are going to do a max of this value with the minimum rgb9e5 exponent
 107    that will hide these problem cases. */
 108 static int FloorLog2(float x)
 109 {
 110    float754 f;
 111
 112    f.value = x;
 113    return (f.field.biasedexponent - 127);
 114 }
 115
 116 unsigned float3_to_rgb9e5(const float rgb[3])
 117 {
 118    rgb9e5 retval;
 119    float maxrgb;
 120    int rm, gm, bm;
 121    float rc, gc, bc;
 122    int exp_shared, maxm;
 123    double denom;
 124
 125    rc = ClampRange_for_rgb9e5(rgb[0]);
 126    gc = ClampRange_for_rgb9e5(rgb[1]);
 127    bc = ClampRange_for_rgb9e5(rgb[2]);
 128
 129    maxrgb = MaxOf3(rc, gc, bc);
 130    exp_shared = MAX2(-RGB9E5_EXP_BIAS-1, FloorLog2(maxrgb)) + 1 + RGB9E5_EXP_BIAS;
 131    assert(exp_shared <= RGB9E5_MAX_VALID_BIASED_EXP);
 132    assert(exp_shared >= 0);
 133    /* This pow function could be replaced by a table. */
 134    denom = pow(2, exp_shared - RGB9E5_EXP_BIAS - RGB9E5_MANTISSA_BITS);
 135
 136    maxm = (int) floor(maxrgb / denom + 0.5);
 137    if (maxm == MAX_RGB9E5_MANTISSA+1) {
 138       denom *= 2;
 139       exp_shared += 1;
 140       assert(exp_shared <= RGB9E5_MAX_VALID_BIASED_EXP);
 141    } else {
 142       assert(maxm <= MAX_RGB9E5_MANTISSA);
 143    }
 144
 145    rm = (int) floor(rc / denom + 0.5);
 146    gm = (int) floor(gc / denom + 0.5);
 147    bm = (int) floor(bc / denom + 0.5);
 148
 149    assert(rm <= MAX_RGB9E5_MANTISSA);
 150    assert(gm <= MAX_RGB9E5_MANTISSA);
 151    assert(bm <= MAX_RGB9E5_MANTISSA);
 152    assert(rm >= 0);
 153    assert(gm >= 0);
 154    assert(bm >= 0);
 155
 156    retval.field.r = rm;
 157    retval.field.g = gm;
 158    retval.field.b = bm;
 159    retval.field.biasedexponent = exp_shared;
 160
 161    return retval.raw;
 162 }
 163
 164 void rgb9e5_to_float3(unsigned rgb, float retval[3])
 165 {
 166    rgb9e5 v;
 167    int exponent;
 168    float scale;
 169
 170    v.raw = rgb;
 171    exponent = v.field.biasedexponent - RGB9E5_EXP_BIAS - RGB9E5_MANTISSA_BITS;
 172    scale = (float) pow(2, exponent);
 173
 174    retval[0] = v.field.r * scale;
 175    retval[1] = v.field.g * scale;
 176    retval[2] = v.field.b * scale;
 177 }