Java floor floor10(double a)

Description

Returns the largest (closest to positive infinity) double value that is a power of 10 not greater than the argument.

License

BSD License

Parameter

Parameter	Description
a	a number greater than 0.0

Return

the largest double value that is a power of 10 not greater than the argument

Declaration

public static double floor10(double a)

Method Source Code

//package com.java2s;
//License from project: BSD License 

public class Main {
    /** Natural log of 10, used in {@code log10} function. */
    public static final double L10 = Math.log(10.0);

    /**// w  ww. j a  v  a  2s  . c  o  m
     * Returns the largest (closest to positive infinity) double value
     * that is a power of 10 not greater than the argument.  Special
     * cases:
     * <ul>
     *   <li>If the argument value is already equal to a power of 10,
     *   then the result is the same as the argument.</li>
     *   <li>If the argument is NaN or an infinity or positive zero or
     *   negative zero, then the result is the same as the
     *   argument.</li>
     * </ul>
     *
     * @param a a number greater than 0.0
     * @return the largest double value that is a power of 10 not
     * greater than the argument
     */
    public static double floor10(double a) {
        return Math.pow(10, Math.floor(log10(a)));
    }

    /**
     * Raises first argument to the power of the second argument.
     *
     * @param x value to raise
     * @param y amount to raise to
     * @return <code>x<sup>y</sup></code>
     */
    public static float pow(float x, int y) {
        float val = 1.0f;
        for (int i = 0; i < Math.abs(y); i++) {
            val *= x;
        }
        if (y < 0) {
            return 1.0f / val;
        }
        return val;
    }

    /**
     * Returns the log base 10 of <code>a</code> double value.
     *
     * @param a a number greater than 0.0
     * @return the value {@code log<sub>10</sub>(a)}
     */
    public static double log10(double a) {
        return Math.log(a) / L10;
    }
}