net.algart.matrices.spectra.RootsOfUnity Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of algart Show documentation
Show all versions of algart Show documentation
Open-source Java libraries, supporting generalized smart arrays and matrices with elements
of any types, including a wide set of 2D-, 3D- and multidimensional image processing
and other algorithms, working with arrays and matrices.
/*
* The MIT License (MIT)
*
* Copyright (c) 2007-2024 Daniel Alievsky, AlgART Laboratory (http://algart.net)
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
package net.algart.matrices.spectra;
class RootsOfUnity {
public static final int LOG_CACHE_SIZE = 20;
public static final int HALF_CACHE_SIZE = 1 << (LOG_CACHE_SIZE - 1);
public static final int CACHE_SIZE = 2 * HALF_CACHE_SIZE;
public static final double[] SINE_CACHE = new double[HALF_CACHE_SIZE + 1];
public static final double[] LOGARITHMICAL_SINE_CACHE = new double[65];
static {
SINE_CACHE[0] = 0.0;
for (int k = 1; k < HALF_CACHE_SIZE; k++) {
SINE_CACHE[k] = StrictMath.sin(0.5 * StrictMath.PI * k / HALF_CACHE_SIZE);
}
SINE_CACHE[HALF_CACHE_SIZE] = 1.0;
}
static {
LOGARITHMICAL_SINE_CACHE[0] = 0.0; // sin(PI)
LOGARITHMICAL_SINE_CACHE[1] = 1.0; // sin(PI/2)
double angle = 0.25 * StrictMath.PI;
for (int log = 2; log <= 64; log++) {
LOGARITHMICAL_SINE_CACHE[log] = StrictMath.sin(angle);
angle *= 0.5;
}
}
/**
* Returns sin φ, φ = π*angleIndex/{@link #CACHE_SIZE}.
* The angleIndex must be in range 0<=angleIndex<={@link #CACHE_SIZE},
* so 0≤φ≤π.
*
* @param angleIndex the angle φ, measured in π/{@link #CACHE_SIZE} units
* (φ = π*angleIndex/{@link #CACHE_SIZE}).
* @return sin φ.
* @throws IndexOutOfBoundsException if angleIndex is not
* in 0..{@link #CACHE_SIZE} range.
*/
public static double quickSin(int angleIndex) {
return angleIndex < HALF_CACHE_SIZE ?
SINE_CACHE[angleIndex] :
SINE_CACHE[2 * HALF_CACHE_SIZE - angleIndex];
}
/**
* Returns cos φ, φ = π*angleIndex/{@link #CACHE_SIZE}.
* The angleIndex must be in range 0<=angleIndex<={@link #CACHE_SIZE},
* so 0≤φ≤π.
*
* @param angleIndex the angle φ, measured in π/{@link #CACHE_SIZE} units
* (φ = π*angleIndex/{@link #CACHE_SIZE}).
* @return cos φ.
* @throws IndexOutOfBoundsException if angleIndex is not
* in 0..{@link #CACHE_SIZE} range.
*/
public static double quickCos(int angleIndex) {
return angleIndex < HALF_CACHE_SIZE ?
SINE_CACHE[HALF_CACHE_SIZE - angleIndex] :
-SINE_CACHE[angleIndex - HALF_CACHE_SIZE];
}
}