src/util/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 static inline int rgb9e5_ClampRange(float x)
  61 {
  62    float754 f;
  63    float754 max;
  64    f.value = x;
  65    max.value = MAX_RGB9E5;
  66
  67    if (f.raw > 0x7f800000)
  68   /* catches neg, NaNs */
  69       return 0;
  70    else if (f.raw >= max.raw)
  71       return max.raw;
  72    else
  73       return f.raw;
  74 }
  75
  76 static inline unsigned int float3_to_rgb9e5(const float rgb[3])
  77 {
  78    int rm, gm, bm, exp_shared;
  79    float754 revdenom = {0};
  80    float754 rc, bc, gc, maxrgb;
  81
  82    rc.raw = rgb9e5_ClampRange(rgb[0]);
  83    gc.raw = rgb9e5_ClampRange(rgb[1]);
  84    bc.raw = rgb9e5_ClampRange(rgb[2]);
  85    maxrgb.raw = MAX3(rc.raw, gc.raw, bc.raw);
  86
  87    /*
  88     * Compared to what the spec suggests, instead of conditionally adjusting
  89     * the exponent after the fact do it here by doing the equivalent of +0.5 -
  90     * the int add will spill over into the exponent in this case.
  91     */
  92    maxrgb.raw += maxrgb.raw & (1 << (23-9));
  93    exp_shared = MAX2((maxrgb.raw >> 23), -RGB9E5_EXP_BIAS - 1 + 127) +
  94                 1 + RGB9E5_EXP_BIAS - 127;
  95    revdenom.field.biasedexponent = 127 - (exp_shared - RGB9E5_EXP_BIAS -
  96                                           RGB9E5_MANTISSA_BITS) + 1;
  97    assert(exp_shared <= RGB9E5_MAX_VALID_BIASED_EXP);
  98
  99    /*
 100     * The spec uses strict round-up behavior (d3d10 disagrees, but in any case
 101     * must match what is done above for figuring out exponent).
 102     * We avoid the doubles ((int) rc * revdenom + 0.5) by doing the rounding
 103     * ourselves (revdenom was adjusted by +1, above).
 104     */
 105    rm = (int) (rc.value * revdenom.value);
 106    gm = (int) (gc.value * revdenom.value);
 107    bm = (int) (bc.value * revdenom.value);
 108    rm = (rm & 1) + (rm >> 1);
 109    gm = (gm & 1) + (gm >> 1);
 110    bm = (bm & 1) + (bm >> 1);
 111
 112    assert(rm <= MAX_RGB9E5_MANTISSA);
 113    assert(gm <= MAX_RGB9E5_MANTISSA);
 114    assert(bm <= MAX_RGB9E5_MANTISSA);
 115    assert(rm >= 0);
 116    assert(gm >= 0);
 117    assert(bm >= 0);
 118
 119    return (exp_shared << 27) | (bm << 18) | (gm << 9) | rm;
 120 }
 121
 122 static inline void rgb9e5_to_float3(unsigned rgb, float retval[3])
 123 {
 124    int exponent;
 125    float754 scale = {0};
 126
 127    exponent = (rgb >> 27) - RGB9E5_EXP_BIAS - RGB9E5_MANTISSA_BITS;
 128    scale.field.biasedexponent = exponent + 127;
 129
 130    retval[0] = ( rgb        & 0x1ff) * scale.value;
 131    retval[1] = ((rgb >> 9)  & 0x1ff) * scale.value;
 132    retval[2] = ((rgb >> 18) & 0x1ff) * scale.value;
 133 }
 134
 135 #endif