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/*
* Copyright (C) 2021 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 android.util;
/**
* SparseDoubleArrays map integers to doubles. Unlike a normal array of doubles,
* there can be gaps in the indices. It is intended to be more memory efficient
* than using a HashMap to map Integers to Doubles, both because it avoids
* auto-boxing keys and values and its data structure doesn't rely on an extra entry object
* for each mapping.
*
* <p>Note that this container keeps its mappings in an array data structure,
* using a binary search to find keys. The implementation is not intended to be appropriate for
* data structures
* that may contain large numbers of items. It is generally slower than a traditional
* HashMap, since lookups require a binary search and adds and removes require inserting
* and deleting entries in the array. For containers holding up to hundreds of items,
* the performance difference is not significant, less than 50%.</p>
*
* <p>It is possible to iterate over the items in this container using
* {@link #keyAt(int)} and {@link #valueAt(int)}. Iterating over the keys using
* <code>keyAt(int)</code> with ascending values of the index will return the
* keys in ascending order, or the values corresponding to the keys in ascending
* order in the case of <code>valueAt(int)</code>.</p>
*
* @see SparseLongArray
*
* @hide
*/
public class SparseDoubleArray implements Cloneable {
/**
* The int->double map, but storing the doubles as longs using
* {@link Double#doubleToRawLongBits(double)}.
*/
private SparseLongArray mValues;
/** Creates a new SparseDoubleArray containing no mappings. */
public SparseDoubleArray() {
this(10);
}
/**
* Creates a new SparseDoubleArray, containing no mappings, that will not
* require any additional memory allocation to store the specified
* number of mappings. If you supply an initial capacity of 0, the
* sparse array will be initialized with a light-weight representation
* not requiring any additional array allocations.
*/
public SparseDoubleArray(int initialCapacity) {
mValues = new SparseLongArray(initialCapacity);
}
@Override
public SparseDoubleArray clone() {
SparseDoubleArray clone = null;
try {
clone = (SparseDoubleArray) super.clone();
clone.mValues = mValues.clone();
} catch (CloneNotSupportedException cnse) {
/* ignore */
}
return clone;
}
/**
* Gets the double mapped from the specified key, or <code>0</code>
* if no such mapping has been made.
*/
public double get(int key) {
final int index = mValues.indexOfKey(key);
if (index < 0) {
return 0.0d;
}
return valueAt(index);
}
/**
* Adds a mapping from the specified key to the specified value,
* replacing the previous mapping from the specified key if there
* was one.
*/
public void put(int key, double value) {
mValues.put(key, Double.doubleToRawLongBits(value));
}
/**
* Adds a mapping from the specified key to the specified value,
* <b>adding</b> its value to the previous mapping from the specified key if there
* was one.
*
* <p>This differs from {@link #put} because instead of replacing any previous value, it adds
* (in the numerical sense) to it.
*/
public void add(int key, double summand) {
final double oldValue = get(key);
put(key, oldValue + summand);
}
/** Returns the number of key-value mappings that this SparseDoubleArray currently stores. */
public int size() {
return mValues.size();
}
/**
* Given an index in the range <code>0...size()-1</code>, returns
* the key from the <code>index</code>th key-value mapping that this
* SparseDoubleArray stores.
*
* @see SparseLongArray#keyAt(int)
*/
public int keyAt(int index) {
return mValues.keyAt(index);
}
/**
* Given an index in the range <code>0...size()-1</code>, returns
* the value from the <code>index</code>th key-value mapping that this
* SparseDoubleArray stores.
*
* @see SparseLongArray#valueAt(int)
*/
public double valueAt(int index) {
return Double.longBitsToDouble(mValues.valueAt(index));
}
/**
* {@inheritDoc}
*
* <p>This implementation composes a string by iterating over its mappings.
*/
@Override
public String toString() {
if (size() <= 0) {
return "{}";
}
StringBuilder buffer = new StringBuilder(size() * 34);
buffer.append('{');
for (int i = 0; i < size(); i++) {
if (i > 0) {
buffer.append(", ");
}
int key = keyAt(i);
buffer.append(key);
buffer.append('=');
double value = valueAt(i);
buffer.append(value);
}
buffer.append('}');
return buffer.toString();
}
}
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