/*
* Copyright (C) 2007 The Android Open Source Project
*
* 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.
*/
package com.android.dx.util;
/**
* Utilities for treating {@code int[]}s as bit sets.
*/
public final class Bits {
/**
* This class is uninstantiable.
*/
private Bits() {
// This space intentionally left blank.
}
/**
* Constructs a bit set to contain bits up to the given index (exclusive).
*
* @param max {@code >= 0;} the maximum bit index (exclusive)
* @return {@code non-null;} an appropriately-constructed instance
*/
public static int[] makeBitSet(int max) {
int size = (max + 0x1f) >> 5;
return new int[size];
}
/**
* Gets the maximum index (exclusive) for the given bit set.
*
* @param bits {@code non-null;} bit set in question
* @return {@code >= 0;} the maximum index (exclusive) that may be set
*/
public static int getMax(int[] bits) {
return bits.length * 0x20;
}
/**
* Gets the value of the bit at the given index.
*
* @param bits {@code non-null;} bit set to operate on
* @param idx {@code >= 0, < getMax(set);} which bit
* @return the value of the indicated bit
*/
public static boolean get(int[] bits, int idx) {
int arrayIdx = idx >> 5;
int bit = 1 << (idx & 0x1f);
return (bits[arrayIdx] & bit) != 0;
}
/**
* Sets the given bit to the given value.
*
* @param bits {@code non-null;} bit set to operate on
* @param idx {@code >= 0, < getMax(set);} which bit
* @param value the new value for the bit
*/
public static void set(int[] bits, int idx, boolean value) {
int arrayIdx = idx >> 5;
int bit = 1 << (idx & 0x1f);
if (value) {
bits[arrayIdx] |= bit;
} else {
bits[arrayIdx] &= ~bit;
}
}
/**
* Sets the given bit to {@code true}.
*
* @param bits {@code non-null;} bit set to operate on
* @param idx {@code >= 0, < getMax(set);} which bit
*/
public static void set(int[] bits, int idx) {
int arrayIdx = idx >> 5;
int bit = 1 << (idx & 0x1f);
bits[arrayIdx] |= bit;
}
/**
* Sets the given bit to {@code false}.
*
* @param bits {@code non-null;} bit set to operate on
* @param idx {@code >= 0, < getMax(set);} which bit
*/
public static void clear(int[] bits, int idx) {
int arrayIdx = idx >> 5;
int bit = 1 << (idx & 0x1f);
bits[arrayIdx] &= ~bit;
}
/**
* Returns whether or not the given bit set is empty, that is, whether
* no bit is set to {@code true}.
*
* @param bits {@code non-null;} bit set to operate on
* @return {@code true} iff all bits are {@code false}
*/
public static boolean isEmpty(int[] bits) {
int len = bits.length;
for (int i = 0; i < len; i++) {
if (bits[i] != 0) {
return false;
}
}
return true;
}
/**
* Gets the number of bits set to {@code true} in the given bit set.
*
* @param bits {@code non-null;} bit set to operate on
* @return {@code >= 0;} the bit count (aka population count) of the set
*/
public static int bitCount(int[] bits) {
int len = bits.length;
int count = 0;
for (int i = 0; i < len; i++) {
count += Integer.bitCount(bits[i]);
}
return count;
}
/**
* Returns whether any bits are set to {@code true} in the
* specified range.
*
* @param bits {@code non-null;} bit set to operate on
* @param start {@code >= 0;} index of the first bit in the range (inclusive)
* @param end {@code >= 0;} index of the last bit in the range (exclusive)
* @return {@code true} if any bit is set to {@code true} in
* the indicated range
*/
public static boolean anyInRange(int[] bits, int start, int end) {
int idx = findFirst(bits, start);
return (idx >= 0) && (idx < end);
}
/**
* Finds the lowest-order bit set at or after the given index in the
* given bit set.
*
* @param bits {@code non-null;} bit set to operate on
* @param idx {@code >= 0;} minimum index to return
* @return {@code >= -1;} lowest-order bit set at or after {@code idx},
* or {@code -1} if there is no appropriate bit index to return
*/
public static int findFirst(int[] bits, int idx) {
int len = bits.length;
int minBit = idx & 0x1f;
for (int arrayIdx = idx >> 5; arrayIdx < len; arrayIdx++) {
int word = bits[arrayIdx];
if (word != 0) {
int bitIdx = findFirst(word, minBit);
if (bitIdx >= 0) {
return (arrayIdx << 5) + bitIdx;
}
}
minBit = 0;
}
return -1;
}
/**
* Finds the lowest-order bit set at or after the given index in the
* given {@code int}.
*
* @param value the value in question
* @param idx 0..31 the minimum bit index to return
* @return {@code >= -1;} lowest-order bit set at or after {@code idx},
* or {@code -1} if there is no appropriate bit index to return
*/
public static int findFirst(int value, int idx) {
value &= ~((1 << idx) - 1); // Mask off too-low bits.
int result = Integer.numberOfTrailingZeros(value);
return (result == 32) ? -1 : result;
}
/**
* Ors bit array {@code b} into bit array {@code a}.
* {@code a.length} must be greater than or equal to
* {@code b.length}.
*
* @param a {@code non-null;} int array to be ored with other argument. This
* argument is modified.
* @param b {@code non-null;} int array to be ored into {@code a}. This
* argument is not modified.
*/
public static void or(int[] a, int[] b) {
for (int i = 0; i < b.length; i++) {
a[i] |= b[i];
}
}
public static String toHuman(int[] bits) {
StringBuilder sb = new StringBuilder();
boolean needsComma = false;
sb.append('{');
int bitsLength = 32 * bits.length;
for (int i = 0; i < bitsLength; i++) {
if (Bits.get(bits, i)) {
if (needsComma) {
sb.append(',');
}
needsComma = true;
sb.append(i);
}
}
sb.append('}');
return sb.toString();
}
}