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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*/
using System;
namespace Lucene.Net.Util
{
/// <summary>Floating point numbers smaller than 32 bits.
///
/// </summary>
/// <version> $Id$
/// </version>
public class SmallFloat
{
/// <summary>Converts a 32 bit float to an 8 bit float.
/// <br/>Values less than zero are all mapped to zero.
/// <br/>Values are truncated (rounded down) to the nearest 8 bit value.
/// <br/>Values between zero and the smallest representable value
/// are rounded up.
///
/// </summary>
/// <param name="f">the 32 bit float to be converted to an 8 bit float (byte)
/// </param>
/// <param name="numMantissaBits">the number of mantissa bits to use in the byte, with the remainder to be used in the exponent
/// </param>
/// <param name="zeroExp">the zero-point in the range of exponent values
/// </param>
/// <returns> the 8 bit float representation
/// </returns>
public static sbyte FloatToByte(float f, int numMantissaBits, int zeroExp)
{
// Adjustment from a float zero exponent to our zero exponent,
// shifted over to our exponent position.
int fzero = (63 - zeroExp) << numMantissaBits;
int bits = System.BitConverter.ToInt32(System.BitConverter.GetBytes(f), 0);
int smallfloat = bits >> (24 - numMantissaBits);
if (smallfloat < fzero)
{
return (bits <= 0)?(sbyte) 0:(sbyte) 1; // underflow is mapped to smallest non-zero number.
}
else if (smallfloat >= fzero + 0x100)
{
return - 1; // overflow maps to largest number
}
else
{
return (sbyte) (smallfloat - fzero);
}
}
/// <summary>Converts an 8 bit float to a 32 bit float. </summary>
public static float ByteToFloat(byte b, int numMantissaBits, int zeroExp)
{
// on Java1.5 & 1.6 JVMs, prebuilding a decoding array and doing a lookup
// is only a little bit faster (anywhere from 0% to 7%)
if (b == 0)
return 0.0f;
int bits = (b & 0xff) << (24 - numMantissaBits);
bits += ((63 - zeroExp) << 24);
return BitConverter.ToSingle(BitConverter.GetBytes(bits), 0);
}
//
// Some specializations of the generic functions follow.
// The generic functions are just as fast with current (1.5)
// -server JVMs, but still slower with client JVMs.
//
/// <summary>floatToByte(b, mantissaBits=3, zeroExponent=15)
/// <br/>smallest non-zero value = 5.820766E-10
/// <br/>largest value = 7.5161928E9
/// <br/>epsilon = 0.125
/// </summary>
public static sbyte FloatToByte315(float f)
{
int bits = System.BitConverter.ToInt32(System.BitConverter.GetBytes(f), 0);
int smallfloat = bits >> (24 - 3);
if (smallfloat < (63 - 15) << 3)
{
return (bits <= 0)?(sbyte) 0:(sbyte) 1;
}
if (smallfloat >= ((63 - 15) << 3) + 0x100)
{
return - 1;
}
return (sbyte) (smallfloat - ((63 - 15) << 3));
}
/// <summary>byteToFloat(b, mantissaBits=3, zeroExponent=15) </summary>
public static float Byte315ToFloat(byte b)
{
// on Java1.5 & 1.6 JVMs, prebuilding a decoding array and doing a lookup
// is only a little bit faster (anywhere from 0% to 7%)
if (b == 0)
return 0.0f;
int bits = (b & 0xff) << (24 - 3);
bits += ((63 - 15) << 24);
return BitConverter.ToSingle(BitConverter.GetBytes(bits), 0);
}
/// <summary>floatToByte(b, mantissaBits=5, zeroExponent=2)
/// <br/>smallest nonzero value = 0.033203125
/// <br/>largest value = 1984.0
/// <br/>epsilon = 0.03125
/// </summary>
public static sbyte FloatToByte52(float f)
{
int bits = System.BitConverter.ToInt32(System.BitConverter.GetBytes(f), 0);
int smallfloat = bits >> (24 - 5);
if (smallfloat < (63 - 2) << 5)
{
return (bits <= 0)?(sbyte) 0:(sbyte) 1;
}
if (smallfloat >= ((63 - 2) << 5) + 0x100)
{
return - 1;
}
return (sbyte) (smallfloat - ((63 - 2) << 5));
}
/// <summary>byteToFloat(b, mantissaBits=5, zeroExponent=2) </summary>
public static float Byte52ToFloat(byte b)
{
// on Java1.5 & 1.6 JVMs, prebuilding a decoding array and doing a lookup
// is only a little bit faster (anywhere from 0% to 7%)
if (b == 0)
return 0.0f;
int bits = (b & 0xff) << (24 - 5);
bits += ((63 - 2) << 24);
return BitConverter.ToSingle(BitConverter.GetBytes(bits), 0);
}
}
}
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