half_float.h

/*
**  ClanLib SDK
**  Copyright (c) 1997-2020 The ClanLib Team
**
**  This software is provided 'as-is', without any express or implied
**  warranty.  In no event will the authors be held liable for any damages
**  arising from the use of this software.
**
**  Permission is granted to anyone to use this software for any purpose,
**  including commercial applications, and to alter it and redistribute it
**  freely, subject to the following restrictions:
**
**  1. The origin of this software must not be misrepresented; you must not
**     claim that you wrote the original software. If you use this software
**     in a product, an acknowledgment in the product documentation would be
**     appreciated but is not required.
**  2. Altered source versions must be plainly marked as such, and must not be
**     misrepresented as being the original software.
**  3. This notice may not be removed or altered from any source distribution.
**
**  Note: Some of the libraries ClanLib may link to may have additional
**  requirements or restrictions.
**
**  File Author(s):
**
**    Magnus Norddahl
*/

#pragma once

namespace clan
{

        class HalfFloat
        {
        public:
                HalfFloat() : value(0)
                {
                }

                HalfFloat(const HalfFloat &other) = default;

                HalfFloat(float v) : value(float_to_half(v))
                {
                }

                HalfFloat &operator =(const HalfFloat &other) = default;

                HalfFloat &operator =(const float v)
                {
                        return from_float(v);
                }

                operator float() const
                {
                        return to_float();
                }

                float to_float() const
                {
                        return half_to_float(value);
                }

                HalfFloat &from_float(float v)
                {
                        value = float_to_half(v);
                        return *this;
                }

                static float half_to_float_simple(unsigned short hf)
                {
                        unsigned int float_value = ((hf & 0x8000) << 16) | (((hf & 0x7c00) + 0x1C000) << 13) | ((hf & 0x03FF) << 13);
                        void *ptr = static_cast<void*>(&float_value);
                        return *static_cast<float*>(ptr);
                }

                static unsigned short float_to_half_simple(float float_value)
                {
                        void *ptr = static_cast<void*>(&float_value);
                        unsigned int f = *static_cast<unsigned int*>(ptr);
                        return ((f >> 16) & 0x8000) | ((((f & 0x7f800000) - 0x38000000) >> 13) & 0x7c00) | ((f >> 13) & 0x03ff);
                }

                static float half_to_float(unsigned short hf)
                {
                        unsigned int float_value = mantissa_table[offset_table[hf >> 10] + (hf & 0x3ff)] + exponent_table[hf >> 10];
                        void *ptr = static_cast<void*>(&float_value);
                        return *static_cast<float*>(ptr);
                }

                static unsigned short float_to_half(float float_value)
                {
                        void *ptr = static_cast<void*>(&float_value);
                        unsigned int f = *static_cast<unsigned int*>(ptr);
                        return base_table[(f >> 23) & 0x1ff] + ((f & 0x007fffff) >> shift_table[(f >> 23) & 0x1ff]);
                }

        private:
                unsigned short value;

                static unsigned int mantissa_table[2048];
                static unsigned int exponent_table[64];
                static unsigned short offset_table[64];

                static unsigned short base_table[512];
                static unsigned char shift_table[512];
        };

}