src/gallium/auxiliary/util/u_format_rgb9e5.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 /* Copied from EXT_texture_shared_exponent and edited, getting rid of
  25  * expensive float math bits too. */
  26
  27 #ifndef RGB9E5_H
  28 #define RGB9E5_H
  29
  30 #include <assert.h>
  31
  32 #include "c99_math.h"
  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
  44 typedef union {
  45    unsigned int raw;
  46    float value;
  47    struct {
  48 #if defined(MESA_BIG_ENDIAN) || defined(PIPE_ARCH_BIG_ENDIAN)
  49       unsigned int negative:1;
  50       unsigned int biasedexponent:8;
  51       unsigned int mantissa:23;
  52 #else
  53       unsigned int mantissa:23;
  54       unsigned int biasedexponent:8;
  55       unsigned int negative:1;
  56 #endif
  57    } field;
  58 } float754;
  59
  60 typedef union {
  61    unsigned int raw;
  62    struct {
  63 #if defined(MESA_BIG_ENDIAN) || defined(PIPE_ARCH_BIG_ENDIAN)
  64       unsigned int biasedexponent:RGB9E5_EXPONENT_BITS;
  65       unsigned int b:RGB9E5_MANTISSA_BITS;
  66       unsigned int g:RGB9E5_MANTISSA_BITS;
  67       unsigned int r:RGB9E5_MANTISSA_BITS;
  68 #else
  69       unsigned int r:RGB9E5_MANTISSA_BITS;
  70       unsigned int g:RGB9E5_MANTISSA_BITS;
  71       unsigned int b:RGB9E5_MANTISSA_BITS;
  72       unsigned int biasedexponent:RGB9E5_EXPONENT_BITS;
  73 #endif
  74    } field;
  75 } rgb9e5;
  76
  77
  78 static inline int rgb9e5_ClampRange(float x)
  79 {
  80    float754 f;
  81    float754 max;
  82    f.value = x;
  83    max.value = MAX_RGB9E5;
  84
  85    if (f.raw > 0x7f800000)
  86   /* catches neg, NaNs */
  87       return 0;
  88    else if (f.raw >= max.raw)
  89       return max.raw;
  90    else
  91       return f.raw;
  92 }
  93
  94 static inline unsigned float3_to_rgb9e5(const float rgb[3])
  95 {
  96    rgb9e5 retval;
  97    int rm, gm, bm, exp_shared;
  98    float754 revdenom = {0};
  99    float754 rc, bc, gc, maxrgb;
 100
 101    rc.raw = rgb9e5_ClampRange(rgb[0]);
 102    gc.raw = rgb9e5_ClampRange(rgb[1]);
 103    bc.raw = rgb9e5_ClampRange(rgb[2]);
 104    maxrgb.raw = MAX3(rc.raw, gc.raw, bc.raw);
 105
 106    /*
 107     * Compared to what the spec suggests, instead of conditionally adjusting
 108     * the exponent after the fact do it here by doing the equivalent of +0.5 -
 109     * the int add will spill over into the exponent in this case.
 110     */
 111    maxrgb.raw += maxrgb.raw & (1 << (23-9));
 112    exp_shared = MAX2((maxrgb.raw >> 23), -RGB9E5_EXP_BIAS - 1 + 127) +
 113                 1 + RGB9E5_EXP_BIAS - 127;
 114    revdenom.field.biasedexponent = 127 - (exp_shared - RGB9E5_EXP_BIAS -
 115                                           RGB9E5_MANTISSA_BITS) + 1;
 116    assert(exp_shared <= RGB9E5_MAX_VALID_BIASED_EXP);
 117
 118    /*
 119     * The spec uses strict round-up behavior (d3d10 disagrees, but in any case
 120     * must match what is done above for figuring out exponent).
 121     * We avoid the doubles ((int) rc * revdenom + 0.5) by doing the rounding
 122     * ourselves (revdenom was adjusted by +1, above).
 123     */
 124    rm = (int) (rc.value * revdenom.value);
 125    gm = (int) (gc.value * revdenom.value);
 126    bm = (int) (bc.value * revdenom.value);
 127    rm = (rm & 1) + (rm >> 1);
 128    gm = (gm & 1) + (gm >> 1);
 129    bm = (bm & 1) + (bm >> 1);
 130
 131    assert(rm <= MAX_RGB9E5_MANTISSA);
 132    assert(gm <= MAX_RGB9E5_MANTISSA);
 133    assert(bm <= MAX_RGB9E5_MANTISSA);
 134    assert(rm >= 0);
 135    assert(gm >= 0);
 136    assert(bm >= 0);
 137
 138    retval.field.r = rm;
 139    retval.field.g = gm;
 140    retval.field.b = bm;
 141    retval.field.biasedexponent = exp_shared;
 142
 143    return retval.raw;
 144 }
 145
 146 static inline void rgb9e5_to_float3(unsigned rgb, float retval[3])
 147 {
 148    rgb9e5 v;
 149    int exponent;
 150    float754 scale = {0};
 151
 152    v.raw = rgb;
 153    exponent = v.field.biasedexponent - RGB9E5_EXP_BIAS - RGB9E5_MANTISSA_BITS;
 154    scale.field.biasedexponent = exponent + 127;
 155
 156    retval[0] = v.field.r * scale.value;
 157    retval[1] = v.field.g * scale.value;
 158    retval[2] = v.field.b * scale.value;
 159 }
 160
 161 #endif