package de.intevation.flys.utils;

import java.util.Arrays;

import de.intevation.flys.artifacts.math.Linear;


public class DoubleUtil
{
    public static final double DEFAULT_STEP_PRECISION = 1e6;

    private DoubleUtil() {
    }

    public static final double [] explode(double from, double to, double step) {
        return explode(from, to, step, DEFAULT_STEP_PRECISION);
    }

    public static final double round(double x, double precision) {
        return Math.round(x * precision)/precision;
    }

    public static final double round(double x) {
        return Math.round(x * DEFAULT_STEP_PRECISION)/DEFAULT_STEP_PRECISION;
    }

    public static final double [] explode(
        double from,
        double to,
        double step,
        double precision
    ) {
        double lower = from;

        double diff = to - from;
        double tmp  = diff / step;
        int    num = (int)Math.abs(Math.ceil(tmp)) + 1;

        double [] values = new double[num];

        if (from > to) {
            step = -step;
        }

        double max = Math.max(from, to);

        for (int idx = 0; idx < num; idx++) {
            if (lower > max) {
                return Arrays.copyOfRange(values, 0, idx);
            }

            values[idx] = round(lower, precision);
            lower      += step;
        }

        return values;
    }

    public static final double interpolateSorted(
        double [] xs,
        double [] ys,
        double x
    ) {
        int lo = 0, hi = xs.length-1;

        int mid = -1;

        while (lo <= hi) {
            mid = (lo + hi) >> 1;
            double mx = xs[mid];
                 if (x < mx) hi = mid - 1;
            else if (x > mx) lo = mid + 1;
            else return ys[mid];
        }
        if (mid < lo) {
            return lo >= xs.length
                ? Double.NaN
                : Linear.linear(x, xs[mid], xs[mid+1], ys[mid], ys[mid+1]);
        }
        return hi < 0
            ? Double.NaN
            : Linear.linear(x, xs[mid-1], xs[mid], ys[mid-1], ys[mid]);
    }
}
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