微软的代码越来越高深莫测了

//微软的代码越来越高深莫测了
private static int IndexOf(IEnumerable items, string parameterName)
{
    if (items != null)
    {
        int num = 0;
        foreach (SqlParameter parameter2 in items)
        {
            if (ADP.SrcCompare(parameterName, parameter2.ParameterName) == 0)
            {
                return num;
            }
            num++;
        }
        num = 0;
        foreach (SqlParameter parameter in items)
        {
            if (ADP.DstCompare(parameterName, parameter.ParameterName) == 0)
            {
                return num;
            }
            num++;
        }
    }
    return -1;
}

protected override DbParameter GetParameter(string parameterName)
{
    int index = this.IndexOf(parameterName);
    if (index < 0)
    {
        throw ADP.ParametersSourceIndex(parameterName, this, ItemType);
    }
    return this.InnerList[index];
}