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Lucene example source code file (SmallFloat.java)

This example Lucene source code file (SmallFloat.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lucene tags/keywords

smallfloat, smallfloat

The Lucene SmallFloat.java source code

package org.apache.lucene.util;
/**
 * Copyright 2005 The Apache Software Foundation
 *
 * 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.
 */


/** Floating point numbers smaller than 32 bits.
 *
 * @lucene.internal
 */
public class SmallFloat {

  /** 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.
   *
   * @param f the 32 bit float to be converted to an 8 bit float (byte)
   * @param numMantissaBits the number of mantissa bits to use in the byte, with the remainder to be used in the exponent
   * @param zeroExp the zero-point in the range of exponent values
   * @return the 8 bit float representation
   */
  public static byte 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)< (24-numMantissaBits);
    if (smallfloat <= fzero) {
      return (bits<=0) ?
        (byte)0   // negative numbers and zero both map to 0 byte
       :(byte)1;  // underflow is mapped to smallest non-zero number.
    } else if (smallfloat >= fzero + 0x100) {
      return -1;  // overflow maps to largest number
    } else {
      return (byte)(smallfloat - fzero);
    }
  }

  /** Converts an 8 bit float to a 32 bit float. */
  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 Float.intBitsToFloat(bits);
  }


  //
  // 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.
  //

  /** floatToByte(b, mantissaBits=3, zeroExponent=15)
   * <br>smallest non-zero value = 5.820766E-10
   * <br>largest value = 7.5161928E9
   * <br>epsilon = 0.125
   */
  public static byte floatToByte315(float f) {
    int bits = Float.floatToRawIntBits(f);
    int smallfloat = bits >> (24-3);
    if (smallfloat <= ((63-15)<<3)) {
      return (bits<=0) ? (byte)0 : (byte)1;
    }
    if (smallfloat >= ((63-15)<<3) + 0x100) {
      return -1;
    }
    return (byte)(smallfloat - ((63-15)<<3));
 }

  /** byteToFloat(b, mantissaBits=3, zeroExponent=15) */
  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 Float.intBitsToFloat(bits);
  }


  /** floatToByte(b, mantissaBits=5, zeroExponent=2)
   * <br>smallest nonzero value = 0.033203125
   * <br>largest value = 1984.0
   * <br>epsilon = 0.03125
   */
  public static byte floatToByte52(float f) {
    int bits = Float.floatToRawIntBits(f);
    int smallfloat = bits >> (24-5);
    if (smallfloat <= (63-2)<<5) {
      return (bits<=0) ? (byte)0 : (byte)1;
    }
    if (smallfloat >= ((63-2)<<5) + 0x100) {
      return -1;
    }
    return (byte)(smallfloat - ((63-2)<<5));
  }

  /** byteToFloat(b, mantissaBits=5, zeroExponent=2) */
  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 Float.intBitsToFloat(bits);
  }
}

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