FastMath.java

package com.artemis.utils;

public class FastMath {
	public static final double PI = Math.PI;
	public static final double SQUARED_PI = PI * PI;
	public static final double HALF_PI = 0.5 * PI;
	public static final double TWO_PI = 2.0 * PI;
	public static final double THREE_PI_HALVES = TWO_PI - HALF_PI;

	private static final double _sin_a = -4 / SQUARED_PI;
	private static final double _sin_b = 4 / PI;
	private static final double _sin_p = 9d / 40;

	private final static double _asin_a = -0.0481295276831013447d;
	private final static double _asin_b = -0.343835993947915197d;
	private final static double _asin_c = 0.962761848425913169d;
	private final static double _asin_d = 1.00138940860107040d;

	private final static double _atan_a = 0.280872d;

	public final static double cos(final double x) {
		return sin(x + ((x > HALF_PI) ? -THREE_PI_HALVES : HALF_PI));
	}

	public final static double sin(double x) {
		x = _sin_a * x * Math.abs(x) + _sin_b * x;
		return _sin_p * (x * Math.abs(x) - x) + x;
	}

	public final static double tan(final double x) {
		return sin(x) / cos(x);
	}

	public final static double asin(final double x) {
		return x * (Math.abs(x) * (Math.abs(x) * _asin_a + _asin_b) + _asin_c) + Math.signum(x) * (_asin_d - Math.sqrt(1 - x * x));
	}

	public final static double acos(final double x) {
		return HALF_PI - asin(x);
	}

	public final static double atan(final double x) {
		return (Math.abs(x) < 1) ? x / (1 + _atan_a * x * x) : Math.signum(x) * HALF_PI - x / (x * x + _atan_a);
	}

	public final static double inverseSqrt(double x) {
		final double xhalves = 0.5d * x;
		x = Double.longBitsToDouble(0x5FE6EB50C7B537AAl - (Double.doubleToRawLongBits(x) >> 1));
		return x * (1.5d - xhalves * x * x); // more iterations possible
	}

	public final static double sqrt(final double x) {
		return x * inverseSqrt(x);
	}

}