BitUtils.java

// $Id: BitUtils.java,v 1.1 2004/07/29 03:45:31 Dave Exp $
/*
 * BitUtils.java
 * Copyright (C) 2003, 2004 David Clausen
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 *
 */
package net.dclausen.microfloat;

/**
 * Helper class providing bit-shift functions which are used internally by
 * the <code>Float</code> and <code>Double</code> classes.  
 */
final class BitUtils {

  private BitUtils() {
  }
  
  /**
   * Returns the number of contiguous 0 bits starting with the most significant
   * bit of x.
   */
  static int countLeadingZeros(int x) {
    if (x <= 0) {
      if (x == 0) {
        return 32;
      }
      return 0;
    }
    int count = 0;
    if ((x & 0xffff0000) == 0) {
      x <<= 16;
      count = 16;
    }
    if ((x & 0xff000000) == 0) {
      x <<= 8;
      count += 8;
    }
    while (x > 0) {
      count++;
      x <<= 1;
    }
    return count;
  }    

  /**
   * Returns the number of contiguous 0 bits starting with the most significant
   * bit of x.
   */
  static int countLeadingZeros(long x) {
    int c = countLeadingZeros((int) (x >> 32));
    if (c == 32) {
      return countLeadingZeros((int) x) + 32;
    }
    return c;
  }    

  /**
   * Right-shift x by count bits, and if any of the shifted-off bits are 1, 
   * set the least significant bit of the return value to 1.
   */
  static int stickyRightShift(int x, int count) {
    if (count >= 32) {
      return ((x == 0) ? 0 : 1);
    } else if ((x << (32 - count)) == 0) {
      return x >>> count;
    } else {
      return (x >>> count) | 1;
    }
  }

  /**
   * Right-shift x by count bits, and if any of the shifted-off bits are 1, 
   * set the least significant bit of the return value to 1.
   */
  static long stickyRightShift(long x, int count) {
    if (count >= 64) {
      return ((x == 0) ? 0 : 1);
    } else if ((x << (64 - count)) == 0) {
      return x >>> count;
    } else {
      return (x >>> count) | 1;
    }
  }

  /**
   * Right-shift x by count bits, and round the result using half-even rounding.
   */
  static int roundingRightShift(int x, int count) {
    int remainder;
    if (count > 32) {
      return 0;
    } else if (count == 32) {
      remainder = x;
      x = 0;
    } else {
      remainder = x << (32 - count);
      x >>>= count;
    }
    if ((remainder < 0) && ((remainder != 0x80000000) || ((x & 1) == 1))) {
      return x + 1;
    }
    return x;
  }

  /**
   * Right-shift x by count bits, and round the result using half-even rounding.
   */
  static long roundingRightShift(long x, int count) {
    long remainder;
    if (count > 64) {
      return 0;
    } else if (count == 64) {
      remainder = x;
      x = 0;
    } else {
      remainder = x << (64 - count);
      x >>>= count;
    }
    if ((remainder < 0) 
        && ((remainder != 0x8000000000000000L) || ((x & 1) == 1))) {
      return x + 1;
    }
    return x;
  }

}