1 //
2 // Copyright 2013 The ANGLE Project Authors. All rights reserved.
3 // Use of this source code is governed by a BSD-style license that can be
4 // found in the LICENSE file.
5 //
6
7 // mathutil.cpp: Math and bit manipulation functions.
8
9 #include "common/mathutil.h"
10
11 #include <math.h>
12 #include <algorithm>
13
14 namespace gl
15 {
16
17 namespace
18 {
19
20 struct RGB9E5Data
21 {
22 unsigned int R : 9;
23 unsigned int G : 9;
24 unsigned int B : 9;
25 unsigned int E : 5;
26 };
27
28 // B is the exponent bias (15)
29 constexpr int g_sharedexp_bias = 15;
30
31 // N is the number of mantissa bits per component (9)
32 constexpr int g_sharedexp_mantissabits = 9;
33
34 // number of mantissa bits per component pre-biased
35 constexpr int g_sharedexp_biased_mantissabits = g_sharedexp_bias + g_sharedexp_mantissabits;
36
37 // Emax is the maximum allowed biased exponent value (31)
38 constexpr int g_sharedexp_maxexponent = 31;
39
40 constexpr float g_sharedexp_max =
41 ((static_cast<float>(1 << g_sharedexp_mantissabits) - 1) /
42 static_cast<float>(1 << g_sharedexp_mantissabits)) *
43 static_cast<float>(1 << (g_sharedexp_maxexponent - g_sharedexp_bias));
44
45 } // anonymous namespace
46
convertRGBFloatsTo999E5(float red,float green,float blue)47 unsigned int convertRGBFloatsTo999E5(float red, float green, float blue)
48 {
49 const float red_c = std::max<float>(0, std::min(g_sharedexp_max, red));
50 const float green_c = std::max<float>(0, std::min(g_sharedexp_max, green));
51 const float blue_c = std::max<float>(0, std::min(g_sharedexp_max, blue));
52
53 const float max_c = std::max<float>(std::max<float>(red_c, green_c), blue_c);
54 const float exp_p =
55 std::max<float>(-g_sharedexp_bias - 1, floor(log(max_c))) + 1 + g_sharedexp_bias;
56 const int max_s = static_cast<int>(
57 floor((max_c / (pow(2.0f, exp_p - g_sharedexp_biased_mantissabits))) + 0.5f));
58 const int exp_s =
59 static_cast<int>((max_s < pow(2.0f, g_sharedexp_mantissabits)) ? exp_p : exp_p + 1);
60 const float pow2_exp = pow(2.0f, static_cast<float>(exp_s) - g_sharedexp_biased_mantissabits);
61
62 RGB9E5Data output;
63 output.R = static_cast<unsigned int>(floor((red_c / pow2_exp) + 0.5f));
64 output.G = static_cast<unsigned int>(floor((green_c / pow2_exp) + 0.5f));
65 output.B = static_cast<unsigned int>(floor((blue_c / pow2_exp) + 0.5f));
66 output.E = exp_s;
67
68 return bitCast<unsigned int>(output);
69 }
70
convert999E5toRGBFloats(unsigned int input,float * red,float * green,float * blue)71 void convert999E5toRGBFloats(unsigned int input, float *red, float *green, float *blue)
72 {
73 const RGB9E5Data *inputData = reinterpret_cast<const RGB9E5Data *>(&input);
74
75 const float pow2_exp =
76 pow(2.0f, static_cast<float>(inputData->E) - g_sharedexp_biased_mantissabits);
77
78 *red = inputData->R * pow2_exp;
79 *green = inputData->G * pow2_exp;
80 *blue = inputData->B * pow2_exp;
81 }
82
83 } // namespace gl
84