/* parse string options */
ampspec_parse_string(str, func)
{
        local frange = "single";

        if (isstring(str))
        {
                if (strlen(str) > 0)
                {
                        str = tolower(str);

                        switch (str)
                        {
                                case "onesided":
                                case "half":
                                case "single":
                                        frange = "single";
                                        break;

                                case "twosided":
                                case "whole":
                                case "double":
                                        frange = "double";
                                        break;

                                case "center":
                                case "centered":
                                case "centerdc":
                                case "shift":
                                        frange = "shift";
                                        break;

                                default:
                                        error(sprintf("%s - unknown flag '%s'", func, str));
                        }
                }
        }

        return(frange);
}