//

// Copyright (c) 2013 The ANGLE Project Authors. All rights reserved.

// Use of this source code is governed by a BSD-style license that can be

// found in the LICENSE file.

//

// mathutil.cpp: Math and bit manipulation functions.

#include "common/mathutil.h"

#include <algorithm>

#include <math.h>

namespace gl

{

namespace

{

struct RGB9E5Data

{

    unsigned int R : 9;

    unsigned int G : 9;

    unsigned int B : 9;

    unsigned int E : 5;

};

// B is the exponent bias (15)

constexpr int g_sharedexp_bias = 15;

// N is the number of mantissa bits per component (9)

constexpr int g_sharedexp_mantissabits = 9;

// Emax is the maximum allowed biased exponent value (31)

constexpr int g_sharedexp_maxexponent = 31;

constexpr float g_sharedexp_max =

    ((static_cast<float>(1 << g_sharedexp_mantissabits) - 1) /

     static_cast<float>(1 << g_sharedexp_mantissabits)) *

    static_cast<float>(1 << (g_sharedexp_maxexponent - g_sharedexp_bias));

}  // anonymous namespace

unsigned int convertRGBFloatsTo999E5(float red, float green, float blue)

{

    const float red_c = std::max<float>(0, std::min(g_sharedexp_max, red));

    const float green_c = std::max<float>(0, std::min(g_sharedexp_max, green));

    const float blue_c = std::max<float>(0, std::min(g_sharedexp_max, blue));

    const float max_c = std::max<float>(std::max<float>(red_c, green_c), blue_c);

    const float exp_p = std::max<float>(-g_sharedexp_bias - 1, floor(log(max_c))) + 1 + g_sharedexp_bias;

    const int max_s = static_cast<int>(floor((max_c / (pow(2.0f, exp_p - g_sharedexp_bias - g_sharedexp_mantissabits))) + 0.5f));

    const int exp_s = static_cast<int>((max_s < pow(2.0f, g_sharedexp_mantissabits)) ? exp_p : exp_p + 1);

    RGB9E5Data output;

    output.R = static_cast<unsigned int>(floor((red_c / (pow(2.0f, exp_s - g_sharedexp_bias - g_sharedexp_mantissabits))) + 0.5f));

    output.G = static_cast<unsigned int>(floor((green_c / (pow(2.0f, exp_s - g_sharedexp_bias - g_sharedexp_mantissabits))) + 0.5f));

    output.B = static_cast<unsigned int>(floor((blue_c / (pow(2.0f, exp_s - g_sharedexp_bias - g_sharedexp_mantissabits))) + 0.5f));

    output.E = exp_s;

    return bitCast<unsigned int>(output);

}

void convert999E5toRGBFloats(unsigned int input, float *red, float *green, float *blue)

{

    const RGB9E5Data *inputData = reinterpret_cast<const RGB9E5Data*>(&input);

    *red = inputData->R * pow(2.0f, (int)inputData->E - g_sharedexp_bias - g_sharedexp_mantissabits);

    *green = inputData->G * pow(2.0f, (int)inputData->E - g_sharedexp_bias - g_sharedexp_mantissabits);

    *blue = inputData->B * pow(2.0f, (int)inputData->E - g_sharedexp_bias - g_sharedexp_mantissabits);

}

}  // namespace gl