/*
 * Author: Andrey Pokidov
 * License: Apache-2.0
 * Date: 12 Nov 2024
 */

namespace BGC
{
    public class UtilityFP64
    {
        public const double EPSYLON = 4.996003611E-14;
        public const double SQUARE_EPSYLON = EPSYLON * EPSYLON;
        
        public const double EPSYLON_EFFECTIVENESS_LIMIT = 1.0;

        public const double ONE_THIRD = 0.333333333333333333;
        public const double ONE_SIXTH = 0.166666666666666667;
        public const double ONE_NINETH = 0.111111111111111111;

        public const double GOLDEN_RATIO_HIGH = 1.61803398874989485;
        public const double GOLDEN_RATIO_LOW = 0.61803398874989485;

        public static bool IsZero(double value)
        {
            return -EPSYLON <= value && value <= EPSYLON;
        }

        public static bool IsUnit(double value)
        {
            return (1.0 - EPSYLON) <= value && value <= (1.0 + EPSYLON);
        }

        public static bool IsSqareUnit(double square)
        {
            return (1.0 - 2.0 * EPSYLON) <= square && square <= (1.0 + 2.0 * EPSYLON);
        }

        public static bool AreClose(double value1, double value2)
        {
            double difference = value1 - value2;
            double squareValue1 = value1 * value1;
            double squareValue2 = value2 * value2;
            double squareDifference = difference * difference;

            if (squareValue1 <= EPSYLON_EFFECTIVENESS_LIMIT || squareValue2 <= EPSYLON_EFFECTIVENESS_LIMIT) {
                return squareDifference <= SQUARE_EPSYLON;
            }

            return squareDifference <= SQUARE_EPSYLON * squareValue1 && squareDifference <= SQUARE_EPSYLON * squareValue2;
        }
    }
}