Custom sort function

[Sripra deep]

Hi Team,
  I wrote a custom sort function that will read the field value and parse
and returns a float value that will be used for sorting. this field is
indexed, stored and docvalues enabled. my latency increases drastically
from 10ms when the filter loads 50 documents and 200ms when it loads 250
documents and 1sec when it loads 1000 documents.

This is my function:

@Override
public FunctionValues getValues(Map context, LeafReaderContext reader)
throws IOException {
final FunctionValues vals = source.getValues(context, reader);
return new FunctionValues() {
        public float floatVal(int doc) {
        float toRet = isasc ? Float.MAX_VALUE : Float.MIN_VALUE;
        /*
        My custom logic in reading a string array and returning a value out
of some condition checks
        */
        }
    }
}

Can you suggest me some suggestions on this ?

Thanks,
Sripradeep P