source: binary-improvements2/7dtd-server-fixes/src/JSON/JSONNumber.cs@ 392

using System;
using System.Text;

namespace AllocsFixes.JSON {
        public class JsonNumber : JsonValue {
                private readonly double value;

                public JsonNumber (double _value) {
                        value = _value;
                }

                public double GetDouble () {
                        return value;
                }

                public int GetInt () {
                        return (int) Math.Round (value);
                }

                public override void ToString (StringBuilder _stringBuilder, bool _prettyPrint = false, int _currentLevel = 0) {
                        _stringBuilder.Append (value.ToCultureInvariantString ());
                }

                public static JsonNumber Parse (string _json, ref int _offset) {
                        //Log.Out ("ParseNumber enter (" + offset + ")");
                        StringBuilder sbNum = new StringBuilder ();
                        StringBuilder sbExp = null;
                        bool hasDec = false;
                        bool hasExp = false;
                        while (_offset < _json.Length) {
                                if (_json [_offset] >= '0' && _json [_offset] <= '9') {
                                        if (hasExp) {
                                                sbExp.Append (_json [_offset]);
                                        } else {
                                                sbNum.Append (_json [_offset]);
                                        }
                                } else if (_json [_offset] == '.') {
                                        if (hasExp) {
                                                throw new MalformedJsonException ("Decimal separator in exponent");
                                        }

                                        if (hasDec) {
                                                throw new MalformedJsonException ("Multiple decimal separators in number found");
                                        }

                                        if (sbNum.Length == 0) {
                                                throw new MalformedJsonException ("No leading digits before decimal separator found");
                                        }

                                        sbNum.Append ('.');
                                        hasDec = true;
                                } else if (_json [_offset] == '-') {
                                        if (hasExp) {
                                                if (sbExp.Length > 0) {
                                                        throw new MalformedJsonException ("Negative sign in exponent after digits");
                                                }

                                                sbExp.Append (_json [_offset]);
                                        } else {
                                                if (sbNum.Length > 0) {
                                                        throw new MalformedJsonException ("Negative sign in mantissa after digits");
                                                }

                                                sbNum.Append (_json [_offset]);
                                        }
                                } else if (_json [_offset] == 'e' || _json [_offset] == 'E') {
                                        if (hasExp) {
                                                throw new MalformedJsonException ("Multiple exponential markers in number found");
                                        }

                                        if (sbNum.Length == 0) {
                                                throw new MalformedJsonException ("No leading digits before exponential marker found");
                                        }

                                        sbExp = new StringBuilder ();
                                        hasExp = true;
                                } else if (_json [_offset] == '+') {
                                        if (hasExp) {
                                                if (sbExp.Length > 0) {
                                                        throw new MalformedJsonException ("Positive sign in exponent after digits");
                                                }

                                                sbExp.Append (_json [_offset]);
                                        } else {
                                                throw new MalformedJsonException ("Positive sign in mantissa found");
                                        }
                                } else {
                                        if (!StringParsers.TryParseDouble (sbNum.ToString (), out double number)) {
                                                throw new MalformedJsonException ("Mantissa is not a valid decimal (\"" + sbNum + "\")");
                                        }

                                        if (hasExp) {
                                                if (!int.TryParse (sbExp.ToString (), out int exp)) {
                                                        throw new MalformedJsonException ("Exponent is not a valid integer (\"" + sbExp + "\")");
                                                }

                                                number *= Math.Pow (10, exp);
                                        }

                                        //Log.Out ("JSON:Parsed Number: " + number.ToString ());
                                        return new JsonNumber (number);
                                }

                                _offset++;
                        }

                        throw new MalformedJsonException ("End of JSON reached before parsing number finished");
                }

                public override string AsString => value.ToCultureInvariantString ();
                public override int AsInt => GetInt ();
                public override double AsDouble => value;
        }
}