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* Copyright (c) 2002 - 2006 IBM Corporation.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
*******************************************************************************/
/*******************************************************************************
* This file includes material derived from code released by the University of
* California under the terms listed below.
*
* Refinement Analysis Tools is Copyright (c) 2007 The Regents of the
* University of California (Regents). Provided that this notice and
* the following two paragraphs are included in any distribution of
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package com.ibm.wala.util.math;
import com.ibm.wala.util.debug.Assertions;
import com.ibm.wala.util.intset.Bits;
/**
* simple utilities with logarithms
*/
public class Logs {
/**
* @return true iff x == 2^n for some integer n
*/
public static boolean isPowerOf2(int x) {
if (x < 0) {
return false;
} else {
return Bits.populationCount(x) == 1;
}
}
/**
* @param x where x == 2^n for some integer n
*/
public static int log2(int x) throws IllegalArgumentException {
if (!isPowerOf2(x)) {
throw new IllegalArgumentException();
}
int test = 1;
for (int i = 0; i < 31; i++) {
if (test == x) {
return i;
}
test <<= 1;
}
Assertions.UNREACHABLE();
return -1;
}
/** Binary log: finds the smallest power k such that 2^k>=n */
public static int binaryLogUp(int n) {
int k = 0;
while ((1 << k) < n) {
k++;
}
return k;
}
/** Binary log: finds the smallest power k such that 2^k>=n */
public static int binaryLogUp(long n) {
int k = 0;
while ((1 << k) < n) {
k++;
}
return k;
}
}