half_float.h

/*
**  UICore
**  Copyright (c) 1997-2015 The UICore 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 UICore may link to may have additional
**  requirements or restrictions.
**
**  File Author(s):
**
**    Magnus Norddahl
*/

#pragma once

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

        HalfFloat(const HalfFloat &other) : value(other.value)
        {
        }

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

        HalfFloat &operator =(const HalfFloat &other)
        {
            value = other.value;
            return *this;
        }

        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];
    };
}