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With inspiration from other libraries
/*
* 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.commons.math3.transform;
import java.util.Arrays;
import org.apache.commons.math3.complex.Complex;
import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.exception.MathIllegalArgumentException;
import org.apache.commons.math3.exception.util.LocalizedFormats;
/**
* Useful functions for the implementation of various transforms.
*
* @since 3.0
*/
public class TransformUtils {
/**
* Table of the powers of 2 to facilitate binary search lookup.
*
* @see #exactLog2(int)
*/
private static final int[] POWERS_OF_TWO = {
0x00000001, 0x00000002, 0x00000004, 0x00000008, 0x00000010, 0x00000020,
0x00000040, 0x00000080, 0x00000100, 0x00000200, 0x00000400, 0x00000800,
0x00001000, 0x00002000, 0x00004000, 0x00008000, 0x00010000, 0x00020000,
0x00040000, 0x00080000, 0x00100000, 0x00200000, 0x00400000, 0x00800000,
0x01000000, 0x02000000, 0x04000000, 0x08000000, 0x10000000, 0x20000000,
0x40000000
};
/** Private constructor. */
private TransformUtils() {
super();
}
/**
* Multiply every component in the given real array by the
* given real number. The change is made in place.
*
* @param f the real array to be scaled
* @param d the real scaling coefficient
* @return a reference to the scaled array
*/
public static double[] scaleArray(double[] f, double d) {
for (int i = 0; i < f.length; i++) {
f[i] *= d;
}
return f;
}
/**
* Multiply every component in the given complex array by the
* given real number. The change is made in place.
*
* @param f the complex array to be scaled
* @param d the real scaling coefficient
* @return a reference to the scaled array
*/
public static Complex[] scaleArray(Complex[] f, double d) {
for (int i = 0; i < f.length; i++) {
f[i] = new Complex(d * f[i].getReal(), d * f[i].getImaginary());
}
return f;
}
/**
* Builds a new two dimensional array of {@code double} filled with the real
* and imaginary parts of the specified {@link Complex} numbers. In the
* returned array {@code dataRI}, the data is laid out as follows
*
* - {@code dataRI[0][i] = dataC[i].getReal()},
* - {@code dataRI[1][i] = dataC[i].getImaginary()}.
*
*
* @param dataC the array of {@link Complex} data to be transformed
* @return a two dimensional array filled with the real and imaginary parts
* of the specified complex input
*/
public static double[][] createRealImaginaryArray(final Complex[] dataC) {
final double[][] dataRI = new double[2][dataC.length];
final double[] dataR = dataRI[0];
final double[] dataI = dataRI[1];
for (int i = 0; i < dataC.length; i++) {
final Complex c = dataC[i];
dataR[i] = c.getReal();
dataI[i] = c.getImaginary();
}
return dataRI;
}
/**
* Builds a new array of {@link Complex} from the specified two dimensional
* array of real and imaginary parts. In the returned array {@code dataC},
* the data is laid out as follows
*
* - {@code dataC[i].getReal() = dataRI[0][i]},
* - {@code dataC[i].getImaginary() = dataRI[1][i]}.
*
*
* @param dataRI the array of real and imaginary parts to be transformed
* @return an array of {@link Complex} with specified real and imaginary parts.
* @throws DimensionMismatchException if the number of rows of the specified
* array is not two, or the array is not rectangular
*/
public static Complex[] createComplexArray(final double[][] dataRI)
throws DimensionMismatchException{
if (dataRI.length != 2) {
throw new DimensionMismatchException(dataRI.length, 2);
}
final double[] dataR = dataRI[0];
final double[] dataI = dataRI[1];
if (dataR.length != dataI.length) {
throw new DimensionMismatchException(dataI.length, dataR.length);
}
final int n = dataR.length;
final Complex[] c = new Complex[n];
for (int i = 0; i < n; i++) {
c[i] = new Complex(dataR[i], dataI[i]);
}
return c;
}
/**
* Returns the base-2 logarithm of the specified {@code int}. Throws an
* exception if {@code n} is not a power of two.
*
* @param n the {@code int} whose base-2 logarithm is to be evaluated
* @return the base-2 logarithm of {@code n}
* @throws MathIllegalArgumentException if {@code n} is not a power of two
*/
public static int exactLog2(final int n)
throws MathIllegalArgumentException {
int index = Arrays.binarySearch(TransformUtils.POWERS_OF_TWO, n);
if (index < 0) {
throw new MathIllegalArgumentException(
LocalizedFormats.NOT_POWER_OF_TWO_CONSIDER_PADDING,
Integer.valueOf(n));
}
return index;
}
}