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 // Emax is the maximum allowed biased exponent value (31)
35 constexpr int g_sharedexp_maxexponent = 31;
36
37 constexpr float g_sharedexp_max =
38 ((static_cast<float>(1 << g_sharedexp_mantissabits) - 1) /
39 static_cast<float>(1 << g_sharedexp_mantissabits)) *
40 static_cast<float>(1 << (g_sharedexp_maxexponent - g_sharedexp_bias));
41
42 } // anonymous namespace
43
convertRGBFloatsTo999E5(float red,float green,float blue)44 unsigned int convertRGBFloatsTo999E5(float red, float green, float blue)
45 {
46 const float red_c = std::max<float>(0, std::min(g_sharedexp_max, red));
47 const float green_c = std::max<float>(0, std::min(g_sharedexp_max, green));
48 const float blue_c = std::max<float>(0, std::min(g_sharedexp_max, blue));
49
50 const float max_c = std::max<float>(std::max<float>(red_c, green_c), blue_c);
51 const float exp_p =
52 std::max<float>(-g_sharedexp_bias - 1, floor(log(max_c))) + 1 + g_sharedexp_bias;
53 const int max_s = static_cast<int>(
54 floor((max_c / (pow(2.0f, exp_p - g_sharedexp_bias - g_sharedexp_mantissabits))) + 0.5f));
55 const int exp_s =
56 static_cast<int>((max_s < pow(2.0f, g_sharedexp_mantissabits)) ? exp_p : exp_p + 1);
57
58 RGB9E5Data output;
59 output.R = static_cast<unsigned int>(
60 floor((red_c / (pow(2.0f, exp_s - g_sharedexp_bias - g_sharedexp_mantissabits))) + 0.5f));
61 output.G = static_cast<unsigned int>(
62 floor((green_c / (pow(2.0f, exp_s - g_sharedexp_bias - g_sharedexp_mantissabits))) + 0.5f));
63 output.B = static_cast<unsigned int>(
64 floor((blue_c / (pow(2.0f, exp_s - g_sharedexp_bias - g_sharedexp_mantissabits))) + 0.5f));
65 output.E = exp_s;
66
67 return bitCast<unsigned int>(output);
68 }
69
convert999E5toRGBFloats(unsigned int input,float * red,float * green,float * blue)70 void convert999E5toRGBFloats(unsigned int input, float *red, float *green, float *blue)
71 {
72 const RGB9E5Data *inputData = reinterpret_cast<const RGB9E5Data *>(&input);
73
74 *red =
75 inputData->R * pow(2.0f, (int)inputData->E - g_sharedexp_bias - g_sharedexp_mantissabits);
76 *green =
77 inputData->G * pow(2.0f, (int)inputData->E - g_sharedexp_bias - g_sharedexp_mantissabits);
78 *blue =
79 inputData->B * pow(2.0f, (int)inputData->E - g_sharedexp_bias - g_sharedexp_mantissabits);
80 }
81
82 } // namespace gl
83