src/Common/Half.cpp

// Copyright 2016 The SwiftShader Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "Half.hpp"

namespace sw
{
	half::half(float fp32)
	{
		unsigned int fp32i = *(unsigned int*)&fp32;
		unsigned int sign = (fp32i & 0x80000000) >> 16;
		unsigned int abs = fp32i & 0x7FFFFFFF;

		if(abs > 0x47FFEFFF)   // Infinity
		{
			fp16i = sign | 0x7FFF;
		}
		else if(abs < 0x38800000)   // Denormal
		{
			unsigned int mantissa = (abs & 0x007FFFFF) | 0x00800000;
			int e = 113 - (abs >> 23);

			if(e < 24)
			{
				abs = mantissa >> e;
			}
			else
			{
				abs = 0;
			}

			fp16i = sign | (abs + 0x00000FFF + ((abs >> 13) & 1)) >> 13;
		}
		else
		{
			fp16i = sign | (abs + 0xC8000000 + 0x00000FFF + ((abs >> 13) & 1)) >> 13;
		}
	}

	half::operator float() const
	{
		unsigned int fp32i;

		int s = (fp16i >> 15) & 0x00000001;
		int e = (fp16i >> 10) & 0x0000001F;
		int m =  fp16i        & 0x000003FF;

		if(e == 0)
		{
			if(m == 0)
			{
				fp32i = s << 31;

				return (float&)fp32i;
			}
			else
			{
				while(!(m & 0x00000400))
				{
					m <<= 1;
					e -=  1;
				}

				e += 1;
				m &= ~0x00000400;
			}
		}

		e = e + (127 - 15);
		m = m << 13;

		fp32i = (s << 31) | (e << 23) | m;

		return (float&)fp32i;
	}

	half &half::operator=(float f)
	{
		*this = half(f);

		return *this;
	}
}