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Lucene example source code file (BitUtil.java)

This example Lucene source code file (BitUtil.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

a, a, b, b, bitutil, bitutil

The Lucene BitUtil.java source code

/**
 * 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.
 */

package org.apache.lucene.util; // from org.apache.solr.util rev 555343

/**  A variety of high efficiency bit twiddling routines.
 * @lucene.internal
 */
public final class BitUtil {

  private BitUtil() {} // no instance

  /** Returns the number of bits set in the long */
  public static int pop(long x) {
  /* Hacker's Delight 32 bit pop function:
   * http://www.hackersdelight.org/HDcode/newCode/pop_arrayHS.cc
   *
  int pop(unsigned x) {
     x = x - ((x >> 1) & 0x55555555);
     x = (x & 0x33333333) + ((x >> 2) & 0x33333333);
     x = (x + (x >> 4)) & 0x0F0F0F0F;
     x = x + (x >> 8);
     x = x + (x >> 16);
     return x & 0x0000003F;
    }
  ***/

    // 64 bit java version of the C function from above
    x = x - ((x >>> 1) & 0x5555555555555555L);
    x = (x & 0x3333333333333333L) + ((x >>>2 ) & 0x3333333333333333L);
    x = (x + (x >>> 4)) & 0x0F0F0F0F0F0F0F0FL;
    x = x + (x >>> 8);
    x = x + (x >>> 16);
    x = x + (x >>> 32);
    return ((int)x) & 0x7F;
  }

  /*** Returns the number of set bits in an array of longs. */
  public static long pop_array(long A[], int wordOffset, int numWords) {
    /*
    * Robert Harley and David Seal's bit counting algorithm, as documented
    * in the revisions of Hacker's Delight
    * http://www.hackersdelight.org/revisions.pdf
    * http://www.hackersdelight.org/HDcode/newCode/pop_arrayHS.cc
    *
    * This function was adapted to Java, and extended to use 64 bit words.
    * if only we had access to wider registers like SSE from java...
    *
    * This function can be transformed to compute the popcount of other functions
    * on bitsets via something like this:
    * sed 's/A\[\([^]]*\)\]/\(A[\1] \& B[\1]\)/g'
    *
    */
    int n = wordOffset+numWords;
    long tot=0, tot8=0;
    long ones=0, twos=0, fours=0;

    int i;
    for (i = wordOffset; i <= n - 8; i+=8) {
      /***  C macro from Hacker's Delight
       #define CSA(h,l, a,b,c) \
       {unsigned u = a ^ b; unsigned v = c; \
       h = (a & b) | (u & v); l = u ^ v;}
       ***/

      long twosA,twosB,foursA,foursB,eights;

      // CSA(twosA, ones, ones, A[i], A[i+1])
      {
        long b=A[i], c=A[i+1];
        long u=ones ^ b;
        twosA=(ones & b)|( u & c);
        ones=u^c;
      }
      // CSA(twosB, ones, ones, A[i+2], A[i+3])
      {
        long b=A[i+2], c=A[i+3];
        long u=ones^b;
        twosB =(ones&b)|(u&c);
        ones=u^c;
      }
      //CSA(foursA, twos, twos, twosA, twosB)
      {
        long u=twos^twosA;
        foursA=(twos&twosA)|(u&twosB);
        twos=u^twosB;
      }
      //CSA(twosA, ones, ones, A[i+4], A[i+5])
      {
        long b=A[i+4], c=A[i+5];
        long u=ones^b;
        twosA=(ones&b)|(u&c);
        ones=u^c;
      }
      // CSA(twosB, ones, ones, A[i+6], A[i+7])
      {
        long b=A[i+6], c=A[i+7];
        long u=ones^b;
        twosB=(ones&b)|(u&c);
        ones=u^c;
      }
      //CSA(foursB, twos, twos, twosA, twosB)
      {
        long u=twos^twosA;
        foursB=(twos&twosA)|(u&twosB);
        twos=u^twosB;
      }

      //CSA(eights, fours, fours, foursA, foursB)
      {
        long u=fours^foursA;
        eights=(fours&foursA)|(u&foursB);
        fours=u^foursB;
      }
      tot8 += pop(eights);
    }

    // handle trailing words in a binary-search manner...
    // derived from the loop above by setting specific elements to 0.
    // the original method in Hackers Delight used a simple for loop:
    //   for (i = i; i < n; i++)      // Add in the last elements
    //  tot = tot + pop(A[i]);

    if (i<=n-4) {
      long twosA, twosB, foursA, eights;
      {
        long b=A[i], c=A[i+1];
        long u=ones ^ b;
        twosA=(ones & b)|( u & c);
        ones=u^c;
      }
      {
        long b=A[i+2], c=A[i+3];
        long u=ones^b;
        twosB =(ones&b)|(u&c);
        ones=u^c;
      }
      {
        long u=twos^twosA;
        foursA=(twos&twosA)|(u&twosB);
        twos=u^twosB;
      }
      eights=fours&foursA;
      fours=fours^foursA;

      tot8 += pop(eights);
      i+=4;
    }

    if (i<=n-2) {
      long b=A[i], c=A[i+1];
      long u=ones ^ b;
      long twosA=(ones & b)|( u & c);
      ones=u^c;

      long foursA=twos&twosA;
      twos=twos^twosA;

      long eights=fours&foursA;
      fours=fours^foursA;

      tot8 += pop(eights);
      i+=2;
    }

    if (i<n) {
      tot += pop(A[i]);
    }

    tot += (pop(fours)<<2)
            + (pop(twos)<<1)
            + pop(ones)
            + (tot8<<3);

    return tot;
  }

  /** Returns the popcount or cardinality of the two sets after an intersection.
   * Neither array is modified.
   */
  public static long pop_intersect(long A[], long B[], int wordOffset, int numWords) {
    // generated from pop_array via sed 's/A\[\([^]]*\)\]/\(A[\1] \& B[\1]\)/g'
    int n = wordOffset+numWords;
    long tot=0, tot8=0;
    long ones=0, twos=0, fours=0;

    int i;
    for (i = wordOffset; i <= n - 8; i+=8) {
      long twosA,twosB,foursA,foursB,eights;

      // CSA(twosA, ones, ones, (A[i] & B[i]), (A[i+1] & B[i+1]))
      {
        long b=(A[i] & B[i]), c=(A[i+1] & B[i+1]);
        long u=ones ^ b;
        twosA=(ones & b)|( u & c);
        ones=u^c;
      }
      // CSA(twosB, ones, ones, (A[i+2] & B[i+2]), (A[i+3] & B[i+3]))
      {
        long b=(A[i+2] & B[i+2]), c=(A[i+3] & B[i+3]);
        long u=ones^b;
        twosB =(ones&b)|(u&c);
        ones=u^c;
      }
      //CSA(foursA, twos, twos, twosA, twosB)
      {
        long u=twos^twosA;
        foursA=(twos&twosA)|(u&twosB);
        twos=u^twosB;
      }
      //CSA(twosA, ones, ones, (A[i+4] & B[i+4]), (A[i+5] & B[i+5]))
      {
        long b=(A[i+4] & B[i+4]), c=(A[i+5] & B[i+5]);
        long u=ones^b;
        twosA=(ones&b)|(u&c);
        ones=u^c;
      }
      // CSA(twosB, ones, ones, (A[i+6] & B[i+6]), (A[i+7] & B[i+7]))
      {
        long b=(A[i+6] & B[i+6]), c=(A[i+7] & B[i+7]);
        long u=ones^b;
        twosB=(ones&b)|(u&c);
        ones=u^c;
      }
      //CSA(foursB, twos, twos, twosA, twosB)
      {
        long u=twos^twosA;
        foursB=(twos&twosA)|(u&twosB);
        twos=u^twosB;
      }

      //CSA(eights, fours, fours, foursA, foursB)
      {
        long u=fours^foursA;
        eights=(fours&foursA)|(u&foursB);
        fours=u^foursB;
      }
      tot8 += pop(eights);
    }


    if (i<=n-4) {
      long twosA, twosB, foursA, eights;
      {
        long b=(A[i] & B[i]), c=(A[i+1] & B[i+1]);
        long u=ones ^ b;
        twosA=(ones & b)|( u & c);
        ones=u^c;
      }
      {
        long b=(A[i+2] & B[i+2]), c=(A[i+3] & B[i+3]);
        long u=ones^b;
        twosB =(ones&b)|(u&c);
        ones=u^c;
      }
      {
        long u=twos^twosA;
        foursA=(twos&twosA)|(u&twosB);
        twos=u^twosB;
      }
      eights=fours&foursA;
      fours=fours^foursA;

      tot8 += pop(eights);
      i+=4;
    }

    if (i<=n-2) {
      long b=(A[i] & B[i]), c=(A[i+1] & B[i+1]);
      long u=ones ^ b;
      long twosA=(ones & b)|( u & c);
      ones=u^c;

      long foursA=twos&twosA;
      twos=twos^twosA;

      long eights=fours&foursA;
      fours=fours^foursA;

      tot8 += pop(eights);
      i+=2;
    }

    if (i<n) {
      tot += pop((A[i] & B[i]));
    }

    tot += (pop(fours)<<2)
            + (pop(twos)<<1)
            + pop(ones)
            + (tot8<<3);

    return tot;
  }

  /** Returns the popcount or cardinality of the union of two sets.
    * Neither array is modified.
    */
   public static long pop_union(long A[], long B[], int wordOffset, int numWords) {
     // generated from pop_array via sed 's/A\[\([^]]*\)\]/\(A[\1] \| B[\1]\)/g'
     int n = wordOffset+numWords;
     long tot=0, tot8=0;
     long ones=0, twos=0, fours=0;

     int i;
     for (i = wordOffset; i <= n - 8; i+=8) {
       /***  C macro from Hacker's Delight
        #define CSA(h,l, a,b,c) \
        {unsigned u = a ^ b; unsigned v = c; \
        h = (a & b) | (u & v); l = u ^ v;}
        ***/

       long twosA,twosB,foursA,foursB,eights;

       // CSA(twosA, ones, ones, (A[i] | B[i]), (A[i+1] | B[i+1]))
       {
         long b=(A[i] | B[i]), c=(A[i+1] | B[i+1]);
         long u=ones ^ b;
         twosA=(ones & b)|( u & c);
         ones=u^c;
       }
       // CSA(twosB, ones, ones, (A[i+2] | B[i+2]), (A[i+3] | B[i+3]))
       {
         long b=(A[i+2] | B[i+2]), c=(A[i+3] | B[i+3]);
         long u=ones^b;
         twosB =(ones&b)|(u&c);
         ones=u^c;
       }
       //CSA(foursA, twos, twos, twosA, twosB)
       {
         long u=twos^twosA;
         foursA=(twos&twosA)|(u&twosB);
         twos=u^twosB;
       }
       //CSA(twosA, ones, ones, (A[i+4] | B[i+4]), (A[i+5] | B[i+5]))
       {
         long b=(A[i+4] | B[i+4]), c=(A[i+5] | B[i+5]);
         long u=ones^b;
         twosA=(ones&b)|(u&c);
         ones=u^c;
       }
       // CSA(twosB, ones, ones, (A[i+6] | B[i+6]), (A[i+7] | B[i+7]))
       {
         long b=(A[i+6] | B[i+6]), c=(A[i+7] | B[i+7]);
         long u=ones^b;
         twosB=(ones&b)|(u&c);
         ones=u^c;
       }
       //CSA(foursB, twos, twos, twosA, twosB)
       {
         long u=twos^twosA;
         foursB=(twos&twosA)|(u&twosB);
         twos=u^twosB;
       }

       //CSA(eights, fours, fours, foursA, foursB)
       {
         long u=fours^foursA;
         eights=(fours&foursA)|(u&foursB);
         fours=u^foursB;
       }
       tot8 += pop(eights);
     }


     if (i<=n-4) {
       long twosA, twosB, foursA, eights;
       {
         long b=(A[i] | B[i]), c=(A[i+1] | B[i+1]);
         long u=ones ^ b;
         twosA=(ones & b)|( u & c);
         ones=u^c;
       }
       {
         long b=(A[i+2] | B[i+2]), c=(A[i+3] | B[i+3]);
         long u=ones^b;
         twosB =(ones&b)|(u&c);
         ones=u^c;
       }
       {
         long u=twos^twosA;
         foursA=(twos&twosA)|(u&twosB);
         twos=u^twosB;
       }
       eights=fours&foursA;
       fours=fours^foursA;

       tot8 += pop(eights);
       i+=4;
     }

     if (i<=n-2) {
       long b=(A[i] | B[i]), c=(A[i+1] | B[i+1]);
       long u=ones ^ b;
       long twosA=(ones & b)|( u & c);
       ones=u^c;

       long foursA=twos&twosA;
       twos=twos^twosA;

       long eights=fours&foursA;
       fours=fours^foursA;

       tot8 += pop(eights);
       i+=2;
     }

     if (i<n) {
       tot += pop((A[i] | B[i]));
     }

     tot += (pop(fours)<<2)
             + (pop(twos)<<1)
             + pop(ones)
             + (tot8<<3);

     return tot;
   }

  /** Returns the popcount or cardinality of A & ~B
   * Neither array is modified.
   */
  public static long pop_andnot(long A[], long B[], int wordOffset, int numWords) {
    // generated from pop_array via sed 's/A\[\([^]]*\)\]/\(A[\1] \& ~B[\1]\)/g'
    int n = wordOffset+numWords;
    long tot=0, tot8=0;
    long ones=0, twos=0, fours=0;

    int i;
    for (i = wordOffset; i <= n - 8; i+=8) {
      /***  C macro from Hacker's Delight
       #define CSA(h,l, a,b,c) \
       {unsigned u = a ^ b; unsigned v = c; \
       h = (a & b) | (u & v); l = u ^ v;}
       ***/

      long twosA,twosB,foursA,foursB,eights;

      // CSA(twosA, ones, ones, (A[i] & ~B[i]), (A[i+1] & ~B[i+1]))
      {
        long b=(A[i] & ~B[i]), c=(A[i+1] & ~B[i+1]);
        long u=ones ^ b;
        twosA=(ones & b)|( u & c);
        ones=u^c;
      }
      // CSA(twosB, ones, ones, (A[i+2] & ~B[i+2]), (A[i+3] & ~B[i+3]))
      {
        long b=(A[i+2] & ~B[i+2]), c=(A[i+3] & ~B[i+3]);
        long u=ones^b;
        twosB =(ones&b)|(u&c);
        ones=u^c;
      }
      //CSA(foursA, twos, twos, twosA, twosB)
      {
        long u=twos^twosA;
        foursA=(twos&twosA)|(u&twosB);
        twos=u^twosB;
      }
      //CSA(twosA, ones, ones, (A[i+4] & ~B[i+4]), (A[i+5] & ~B[i+5]))
      {
        long b=(A[i+4] & ~B[i+4]), c=(A[i+5] & ~B[i+5]);
        long u=ones^b;
        twosA=(ones&b)|(u&c);
        ones=u^c;
      }
      // CSA(twosB, ones, ones, (A[i+6] & ~B[i+6]), (A[i+7] & ~B[i+7]))
      {
        long b=(A[i+6] & ~B[i+6]), c=(A[i+7] & ~B[i+7]);
        long u=ones^b;
        twosB=(ones&b)|(u&c);
        ones=u^c;
      }
      //CSA(foursB, twos, twos, twosA, twosB)
      {
        long u=twos^twosA;
        foursB=(twos&twosA)|(u&twosB);
        twos=u^twosB;
      }

      //CSA(eights, fours, fours, foursA, foursB)
      {
        long u=fours^foursA;
        eights=(fours&foursA)|(u&foursB);
        fours=u^foursB;
      }
      tot8 += pop(eights);
    }


    if (i<=n-4) {
      long twosA, twosB, foursA, eights;
      {
        long b=(A[i] & ~B[i]), c=(A[i+1] & ~B[i+1]);
        long u=ones ^ b;
        twosA=(ones & b)|( u & c);
        ones=u^c;
      }
      {
        long b=(A[i+2] & ~B[i+2]), c=(A[i+3] & ~B[i+3]);
        long u=ones^b;
        twosB =(ones&b)|(u&c);
        ones=u^c;
      }
      {
        long u=twos^twosA;
        foursA=(twos&twosA)|(u&twosB);
        twos=u^twosB;
      }
      eights=fours&foursA;
      fours=fours^foursA;

      tot8 += pop(eights);
      i+=4;
    }

    if (i<=n-2) {
      long b=(A[i] & ~B[i]), c=(A[i+1] & ~B[i+1]);
      long u=ones ^ b;
      long twosA=(ones & b)|( u & c);
      ones=u^c;

      long foursA=twos&twosA;
      twos=twos^twosA;

      long eights=fours&foursA;
      fours=fours^foursA;

      tot8 += pop(eights);
      i+=2;
    }

    if (i<n) {
      tot += pop((A[i] & ~B[i]));
    }

    tot += (pop(fours)<<2)
            + (pop(twos)<<1)
            + pop(ones)
            + (tot8<<3);

    return tot;
  }

  public static long pop_xor(long A[], long B[], int wordOffset, int numWords) {
    int n = wordOffset+numWords;
    long tot=0, tot8=0;
    long ones=0, twos=0, fours=0;

    int i;
    for (i = wordOffset; i <= n - 8; i+=8) {
      /***  C macro from Hacker's Delight
       #define CSA(h,l, a,b,c) \
       {unsigned u = a ^ b; unsigned v = c; \
       h = (a & b) | (u & v); l = u ^ v;}
       ***/

      long twosA,twosB,foursA,foursB,eights;

      // CSA(twosA, ones, ones, (A[i] ^ B[i]), (A[i+1] ^ B[i+1]))
      {
        long b=(A[i] ^ B[i]), c=(A[i+1] ^ B[i+1]);
        long u=ones ^ b;
        twosA=(ones & b)|( u & c);
        ones=u^c;
      }
      // CSA(twosB, ones, ones, (A[i+2] ^ B[i+2]), (A[i+3] ^ B[i+3]))
      {
        long b=(A[i+2] ^ B[i+2]), c=(A[i+3] ^ B[i+3]);
        long u=ones^b;
        twosB =(ones&b)|(u&c);
        ones=u^c;
      }
      //CSA(foursA, twos, twos, twosA, twosB)
      {
        long u=twos^twosA;
        foursA=(twos&twosA)|(u&twosB);
        twos=u^twosB;
      }
      //CSA(twosA, ones, ones, (A[i+4] ^ B[i+4]), (A[i+5] ^ B[i+5]))
      {
        long b=(A[i+4] ^ B[i+4]), c=(A[i+5] ^ B[i+5]);
        long u=ones^b;
        twosA=(ones&b)|(u&c);
        ones=u^c;
      }
      // CSA(twosB, ones, ones, (A[i+6] ^ B[i+6]), (A[i+7] ^ B[i+7]))
      {
        long b=(A[i+6] ^ B[i+6]), c=(A[i+7] ^ B[i+7]);
        long u=ones^b;
        twosB=(ones&b)|(u&c);
        ones=u^c;
      }
      //CSA(foursB, twos, twos, twosA, twosB)
      {
        long u=twos^twosA;
        foursB=(twos&twosA)|(u&twosB);
        twos=u^twosB;
      }

      //CSA(eights, fours, fours, foursA, foursB)
      {
        long u=fours^foursA;
        eights=(fours&foursA)|(u&foursB);
        fours=u^foursB;
      }
      tot8 += pop(eights);
    }


    if (i<=n-4) {
      long twosA, twosB, foursA, eights;
      {
        long b=(A[i] ^ B[i]), c=(A[i+1] ^ B[i+1]);
        long u=ones ^ b;
        twosA=(ones & b)|( u & c);
        ones=u^c;
      }
      {
        long b=(A[i+2] ^ B[i+2]), c=(A[i+3] ^ B[i+3]);
        long u=ones^b;
        twosB =(ones&b)|(u&c);
        ones=u^c;
      }
      {
        long u=twos^twosA;
        foursA=(twos&twosA)|(u&twosB);
        twos=u^twosB;
      }
      eights=fours&foursA;
      fours=fours^foursA;

      tot8 += pop(eights);
      i+=4;
    }

    if (i<=n-2) {
      long b=(A[i] ^ B[i]), c=(A[i+1] ^ B[i+1]);
      long u=ones ^ b;
      long twosA=(ones & b)|( u & c);
      ones=u^c;

      long foursA=twos&twosA;
      twos=twos^twosA;

      long eights=fours&foursA;
      fours=fours^foursA;

      tot8 += pop(eights);
      i+=2;
    }

    if (i<n) {
      tot += pop((A[i] ^ B[i]));
    }

    tot += (pop(fours)<<2)
            + (pop(twos)<<1)
            + pop(ones)
            + (tot8<<3);

    return tot;
  }

  /* python code to generate ntzTable
  def ntz(val):
    if val==0: return 8
    i=0
    while (val&0x01)==0:
      i = i+1
      val >>= 1
    return i
  print ','.join([ str(ntz(i)) for i in range(256) ])
  ***/
  /** table of number of trailing zeros in a byte */
  public static final byte[] ntzTable = {8,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,5,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,6,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,5,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,7,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,5,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,6,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,5,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0};


  /** Returns number of trailing zeros in a 64 bit long value. */
  public static int ntz(long val) {
    // A full binary search to determine the low byte was slower than
    // a linear search for nextSetBit().  This is most likely because
    // the implementation of nextSetBit() shifts bits to the right, increasing
    // the probability that the first non-zero byte is in the rhs.
    //
    // This implementation does a single binary search at the top level only
    // so that all other bit shifting can be done on ints instead of longs to
    // remain friendly to 32 bit architectures.  In addition, the case of a
    // non-zero first byte is checked for first because it is the most common
    // in dense bit arrays.

    int lower = (int)val;
    int lowByte = lower & 0xff;
    if (lowByte != 0) return ntzTable[lowByte];

    if (lower!=0) {
      lowByte = (lower>>>8) & 0xff;
      if (lowByte != 0) return ntzTable[lowByte] + 8;
      lowByte = (lower>>>16) & 0xff;
      if (lowByte != 0) return ntzTable[lowByte] + 16;
      // no need to mask off low byte for the last byte in the 32 bit word
      // no need to check for zero on the last byte either.
      return ntzTable[lower>>>24] + 24;
    } else {
      // grab upper 32 bits
      int upper=(int)(val>>32);
      lowByte = upper & 0xff;
      if (lowByte != 0) return ntzTable[lowByte] + 32;
      lowByte = (upper>>>8) & 0xff;
      if (lowByte != 0) return ntzTable[lowByte] + 40;
      lowByte = (upper>>>16) & 0xff;
      if (lowByte != 0) return ntzTable[lowByte] + 48;
      // no need to mask off low byte for the last byte in the 32 bit word
      // no need to check for zero on the last byte either.
      return ntzTable[upper>>>24] + 56;
    }
  }

  /** Returns number of trailing zeros in a 32 bit int value. */
  public static int ntz(int val) {
    // This implementation does a single binary search at the top level only.
    // In addition, the case of a non-zero first byte is checked for first
    // because it is the most common in dense bit arrays.

    int lowByte = val & 0xff;
    if (lowByte != 0) return ntzTable[lowByte];
    lowByte = (val>>>8) & 0xff;
    if (lowByte != 0) return ntzTable[lowByte] + 8;
    lowByte = (val>>>16) & 0xff;
    if (lowByte != 0) return ntzTable[lowByte] + 16;
    // no need to mask off low byte for the last byte.
    // no need to check for zero on the last byte either.
    return ntzTable[val>>>24] + 24;
  }

  /** returns 0 based index of first set bit
   * (only works for x!=0)
   * <br/> This is an alternate implementation of ntz()
   */
  public static int ntz2(long x) {
   int n = 0;
   int y = (int)x;
   if (y==0) {n+=32; y = (int)(x>>>32); }   // the only 64 bit shift necessary
   if ((y & 0x0000FFFF) == 0) { n+=16; y>>>=16; }
   if ((y & 0x000000FF) == 0) { n+=8; y>>>=8; }
   return (ntzTable[ y & 0xff ]) + n;
  }

  /** returns 0 based index of first set bit
   * <br/> This is an alternate implementation of ntz()
   */
  public static int ntz3(long x) {
   // another implementation taken from Hackers Delight, extended to 64 bits
   // and converted to Java.
   // Many 32 bit ntz algorithms are at http://www.hackersdelight.org/HDcode/ntz.cc
   int n = 1;

   // do the first step as a long, all others as ints.
   int y = (int)x;
   if (y==0) {n+=32; y = (int)(x>>>32); }
   if ((y & 0x0000FFFF) == 0) { n+=16; y>>>=16; }
   if ((y & 0x000000FF) == 0) { n+=8; y>>>=8; }
   if ((y & 0x0000000F) == 0) { n+=4; y>>>=4; }
   if ((y & 0x00000003) == 0) { n+=2; y>>>=2; }
   return n - (y & 1);
  }

  /** table of number of leading zeros in a byte */
  public static final byte[] nlzTable = {8,7,6,6,5,5,5,5,4,4,4,4,4,4,4,4,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};

  /** Returns the number of leading zero bits.
   */
  public static int nlz(long x) {
   int n = 0;
   // do the first step as a long
   int y = (int)(x>>>32);
   if (y==0) {n+=32; y = (int)(x); }
   if ((y & 0xFFFF0000) == 0) { n+=16; y<<=16; }
   if ((y & 0xFF000000) == 0) { n+=8; y<<=8; }
   return n + nlzTable[y >>> 24];
 /* implementation without table:
   if ((y & 0xF0000000) == 0) { n+=4; y<<=4; }
   if ((y & 0xC0000000) == 0) { n+=2; y<<=2; }
   if ((y & 0x80000000) == 0) { n+=1; y<<=1; }
   if ((y & 0x80000000) == 0) { n+=1;}
   return n;
  */
  }


  /** returns true if v is a power of two or zero*/
  public static boolean isPowerOfTwo(int v) {
    return ((v & (v-1)) == 0);
  }

  /** returns true if v is a power of two or zero*/
  public static boolean isPowerOfTwo(long v) {
    return ((v & (v-1)) == 0);
  }

  /** returns the next highest power of two, or the current value if it's already a power of two or zero*/
  public static int nextHighestPowerOfTwo(int v) {
    v--;
    v |= v >> 1;
    v |= v >> 2;
    v |= v >> 4;
    v |= v >> 8;
    v |= v >> 16;
    v++;
    return v;
  }

  /** returns the next highest power of two, or the current value if it's already a power of two or zero*/
   public static long nextHighestPowerOfTwo(long v) {
    v--;
    v |= v >> 1;
    v |= v >> 2;
    v |= v >> 4;
    v |= v >> 8;
    v |= v >> 16;
    v |= v >> 32;
    v++;
    return v;
  }

}

Other Lucene examples (source code examples)

Here is a short list of links related to this Lucene BitUtil.java source code file:



my book on functional programming

 

new blog posts

 

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