content: 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)<<numMantissaBits;
      int bits = Float.floatToRawIntBits(f);
      int smallfloat = bits >> (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);
    }
  }
  