jellyfin/MediaBrowser.Providers/Photos/PhotoHelper.cs

using System;
using System.Text;

namespace MediaBrowser.Providers.Photos
{
    public static class PhotoHelper
    {
        public static string Dec2Frac(double dbl)
        {
            char neg = ' ';
            double dblDecimal = dbl;
            if (dblDecimal == (int)dblDecimal) return dblDecimal.ToString(); //return no if it's not a decimal
            if (dblDecimal < 0)
            {
                dblDecimal = Math.Abs(dblDecimal);
                neg = '-';
            }
            var whole = (int)Math.Truncate(dblDecimal);
            string decpart = dblDecimal.ToString().Replace(Math.Truncate(dblDecimal) + ".", "");
            double rN = Convert.ToDouble(decpart);
            double rD = Math.Pow(10, decpart.Length);

            string rd = Recur(decpart);
            int rel = Convert.ToInt32(rd);
            if (rel != 0)
            {
                rN = rel;
                rD = (int)Math.Pow(10, rd.Length) - 1;
            }
            //just a few prime factors for testing purposes
            var primes = new[] { 47, 43, 37, 31, 29, 23, 19, 17, 13, 11, 7, 5, 3, 2 };
            foreach (int i in primes) ReduceNo(i, ref rD, ref rN);

            rN = rN + (whole * rD);
            return string.Format("{0}{1}/{2}", neg, rN, rD);
        }

        /// <summary>
        /// Finds out the recurring decimal in a specified number
        /// </summary>
        /// <param name="db">Number to check</param>
        /// <returns></returns>
        private static string Recur(string db)
        {
            if (db.Length < 13) return "0";
            var sb = new StringBuilder();
            for (int i = 0; i < 7; i++)
            {
                sb.Append(db[i]);
                int dlength = (db.Length / sb.ToString().Length);
                int occur = Occurence(sb.ToString(), db);
                if (dlength == occur || dlength == occur - sb.ToString().Length)
                {
                    return sb.ToString();
                }
            }
            return "0";
        }

        /// <summary>
        /// Checks for number of occurence of specified no in a number
        /// </summary>
        /// <param name="s">The no to check occurence times</param>
        /// <param name="check">The number where to check this</param>
        /// <returns></returns>
        private static int Occurence(string s, string check)
        {
            int i = 0;
            int d = s.Length;
            string ds = check;
            for (int n = (ds.Length / d); n > 0; n--)
            {
                if (ds.Contains(s))
                {
                    i++;
                    ds = ds.Remove(ds.IndexOf(s, System.StringComparison.Ordinal), d);
                }
            }
            return i;
        }

        /// <summary>
        /// Reduces a fraction given the numerator and denominator
        /// </summary>
        /// <param name="i">Number to use in an attempt to reduce fraction</param>
        /// <param name="rD">the Denominator</param>
        /// <param name="rN">the Numerator</param>
        private static void ReduceNo(int i, ref double rD, ref double rN)
        {
            //keep reducing until divisibility ends
            while ((rD % i) < 1e-10 && (rN % i) < 1e-10)
            {
                rN = rN / i;
                rD = rD / i;
            }
        }
    }
}