Base93 - Integer Shortening in C#

This post will describe a technique of shortening an integer by approximately 50%.  For example, the approximate coordinate extent of continental United States in web Mercator can be expressed in the following JSON representation.
{"xmin":-15438951,"ymin":1852835,"xmax":-5420194,"ymax":7485635},

…or simplified to:
-15438951,1852835,-5420194,7485635

…or shortened to:
-ji5l,2sk},cGyR,70o#

The principle being employed here is that numbers are normally expressed using the decimal or base ten numerical system.  This system requires ten characters (or “digits”), 0 to 9, to formulate a number.  However, because ASCII has 95 printable characters we can encode numbers using base 93 which can result in printed strings that are 50% shorter than their decimal cousins.  For example:

-15438951 to –ji5l, or
1852835 to 2sk}

Why not use all 128 ASCII characters?  Well. 33 are non-printable and the characters “,” and “-“ are reserved for delimiter and negation respectively.

Lastly, to reduce the overall length of extents, the xmax is expressed as a width and ymax as a height.  At small scales the benefit of this technique is negligible (if any) but significant at large scales.

Please see below for source code and test method.

using System;
using System.Diagnostics;
using System.Globalization;
using System.Linq;

namespace ESRI.PrototypeLab.Base93 {
    public static class Base93Extension {
        private const string CHRS =
            "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ" +
            " !?\"'`^#$%@&*+=/.:;|\\_<>[]{}()~";
        public static string ToShortenedString(this int num) {
            string result = string.Empty;
            if (num < 0) {
                result += "-";
                num = Math.Abs(num);
            }
            int len = CHRS.Length;
            int index = 0;
            while (num >= Math.Pow(len, index)) {
                index++;
            }
            index--;
            while (index >= 0) {
                int pow = (int)Math.Pow(len, index);
                int div = num / pow;
                result += CHRS[div];
                num -= pow * div;
                index--;
            }
            return result;
        }
        public static int ToUncompressedInteger(this string s) {
            int result = 0;
            int len = CHRS.Length;
            int index = 0;
            var chars = s.ToCharArray();
            foreach (char c in chars.Reverse().Where(x => x != '-')) {
                int pow = (int)Math.Pow(len, index);
                int ind = CHRS.IndexOf(c);
                result += pow * ind;
                index++;
            }
            if (chars.First() == '-') {
                result *= -1;
            }
            return result;
        }
        internal static void Test() {
            int max = int.MaxValue;
            string com = max.ToShortenedString();
            int unc = com.ToUncompressedInteger();
            double x = (double)com.Length /
                       (double)max.ToString(CultureInfo.InvariantCulture).Length;
            Debug.WriteLine("Max Integer:  {0}", max);
            Debug.WriteLine("Compressed:   {0}", com);
            Debug.WriteLine("Uncompressed: {0}", unc);
            Debug.WriteLine("Compression:  {0:P}", 1 - x);
        }
    }
}