crc method
Implementation
Map<String,Function> crc() {
int c = -1;
return {
'p': (d) {
// closures have awful performance
int cr = c;
for (int i = 0; i < d.length; ++i){
cr = crct[(cr & 255) ^ d[i]] ^ (cr >>> 8);
}
c = cr;
},
'd': () { return ~c; }
};
}