A simple unix permission symbol parser

simple_unix_permission_symbol_parser.js

// http://jsperf.com/symbolmask

var symbolMask = function(am, ar, aa, as){
    var ir, ia, is, i, j, k,
        s = /[\+\,\s]/,
        m = 0, r = '', 
        l = 1, e = [];
    for(i=0; i<am.length; i++)
        if (s.test(am[i])) {
            (l = am[i] !== '+') && (r = []);
        } else if (l) {
            r = am[i] === 'a' ? ar : r+am[i];
        } else {
            if(as[0]===am[i])
                e[ar.length] |= 1;
            else {
                for(j=r.length;j--;){
                    if((ir = ar.indexOf(r[j])) === -1)
                        throw new Error('Incorret Role token [' + r[j] + ']');
                    if((ia = aa.indexOf(am[i])) === -1 && (is = as.indexOf(am[i])) === -1)
                        throw new Error('Incorret Flag token [' + am[i] + ']');
                    if(ia>-1)
                        e[ir] |= 1 << ia;
                    else
                        for(k=r.length;k--;){
                            e[ar.length] |= (is << (ar.indexOf(r[k])));
                        }
                };
            }
        };
    for(i=ar.length+1;i--;)
        m |= (e[i]||0) << i * aa.length;
    return m;
}


// Uage:
// symbolMask(symbolsPattern <string>, RolesMap <string>, AccessMap <string>, SpecialMap <string>);
// symbolMask('ug+rwxs,o+rwx,+t', 'ogu', 'xwr', 'ts') // 4095 === '7777';