Decompilation issues

Hello all.

I found some significant issues in C# decompilation that prevents from understanding code
Here is one of them.

Assembly: mscorlib, Version=4.0.0.0
Declaring Type: System.IO.StringReader
Method: public override string ReadLine();

Original code taken from http://referencesource.microsoft.com/#mscorlib/system/io/stringreader.cs

        // Reads a line. A line is defined as a sequence of characters followed by
        // a carriage return ('
'), a line feed ('
'), or a carriage return
        // immediately followed by a line feed. The resulting string does not
        // contain the terminating carriage return and/or line feed. The returned
        // value is null if the end of the underlying string has been reached.
        //
        public override String ReadLine() {
            if (_s == null)
                __Error.ReaderClosed();
            int i = _pos;
            while (i < _length) {
                char ch = _s[i];
                if (ch == '
' || ch == '
') {
                    String result = _s.Substring(_pos, i - _pos);
                    _pos = i + 1;
                    if (ch == '
' && _pos < _length && _s[_pos] == '
') _pos++;
                    return result;
                }
                i++;
            }
            if (i > _pos) {
                String result = _s.Substring(_pos, i - _pos);
                _pos = i;
                return result;
            }
            return null;
        }

Decompiled code

public override string ReadLine()
{
    if (this._s == null)
    {
        __Error.ReaderClosed();
    }
    int num = this._pos;
    while (num < this._length)
    {
        char ch = this._s[num];
        switch (ch)
        {
            case '
':
            case '
':
                this._pos = num + 1;
                if (((ch == '
') && (this._pos < this._length)) && (this._s[this._pos] == '
'))
                {
                    this._pos++;
                }
                return this._s.Substring(this._pos, num - this._pos);
        }
        num++;
    }
    if (num > this._pos)
    {
        this._pos = num;
        return this._s.Substring(this._pos, num - this._pos);
    }
    return null;
}