1 //
2 // Copyright (c) 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 <algorithm>
12 #include <math.h>
13
14 namespace gl
15 {
16
17 struct RGB9E5Data
18 {
19 unsigned int R : 9;
20 unsigned int G : 9;
21 unsigned int B : 9;
22 unsigned int E : 5;
23 };
24
25 // B is the exponent bias (15)
26 static const int g_sharedexp_bias = 15;
27
28 // N is the number of mantissa bits per component (9)
29 static const int g_sharedexp_mantissabits = 9;
30
31 // Emax is the maximum allowed biased exponent value (31)
32 static const int g_sharedexp_maxexponent = 31;
33
34 static const float g_sharedexp_max = ((pow(2.0f, g_sharedexp_mantissabits) - 1) /
35 pow(2.0f, g_sharedexp_mantissabits)) *
36 pow(2.0f, g_sharedexp_maxexponent - g_sharedexp_bias);
37
convertRGBFloatsTo999E5(float red,float green,float blue)38 unsigned int convertRGBFloatsTo999E5(float red, float green, float blue)
39 {
40 const float red_c = std::max<float>(0, std::min(g_sharedexp_max, red));
41 const float green_c = std::max<float>(0, std::min(g_sharedexp_max, green));
42 const float blue_c = std::max<float>(0, std::min(g_sharedexp_max, blue));
43
44 const float max_c = std::max<float>(std::max<float>(red_c, green_c), blue_c);
45 const float exp_p = std::max<float>(-g_sharedexp_bias - 1, floor(log(max_c))) + 1 + g_sharedexp_bias;
46 const int max_s = floor((max_c / (pow(2.0f, exp_p - g_sharedexp_bias - g_sharedexp_mantissabits))) + 0.5f);
47 const int exp_s = (max_s < pow(2.0f, g_sharedexp_mantissabits)) ? exp_p : exp_p + 1;
48
49 RGB9E5Data output;
50 output.R = floor((red_c / (pow(2.0f, exp_s - g_sharedexp_bias - g_sharedexp_mantissabits))) + 0.5f);
51 output.G = floor((green_c / (pow(2.0f, exp_s - g_sharedexp_bias - g_sharedexp_mantissabits))) + 0.5f);
52 output.B = floor((blue_c / (pow(2.0f, exp_s - g_sharedexp_bias - g_sharedexp_mantissabits))) + 0.5f);
53 output.E = exp_s;
54
55 return *reinterpret_cast<unsigned int*>(&output);
56 }
57
convert999E5toRGBFloats(unsigned int input,float * red,float * green,float * blue)58 void convert999E5toRGBFloats(unsigned int input, float *red, float *green, float *blue)
59 {
60 const RGB9E5Data *inputData = reinterpret_cast<const RGB9E5Data*>(&input);
61
62 *red = inputData->R * pow(2.0f, (int)inputData->E - g_sharedexp_bias - g_sharedexp_mantissabits);
63 *green = inputData->G * pow(2.0f, (int)inputData->E - g_sharedexp_bias - g_sharedexp_mantissabits);
64 *blue = inputData->B * pow(2.0f, (int)inputData->E - g_sharedexp_bias - g_sharedexp_mantissabits);
65 }
66
67 }
68