csv.java

import java.nio.file.*;
import java.io.*;
import java.util.*;
import java.nio.charset.StandardCharsets;

class csv {

    // i don't want all my fucking int array elements boxed.
    static class IntArray {
        int cnt;
        int[] data;

        IntArray(int init_cap) { data = new int[init_cap]; cnt = 0; }
        void reset() { cnt = 0; }
        int get(int i) { return data[i]; }
        void put(int v) {
            // grow array
            if (cnt == data.length) {
                int[] new_data = new int[cnt * 2];
                System.arraycopy(data, 0, new_data, 0, cnt);
                data = new_data;
            }
            data[cnt++] = v;
        }
    }

    static class CSV {
        // points into data to show where rows start
        IntArray rows;
        // represent slices:
        //   data[parsed[i*2 + 0] .. parsed[i*2 + 1])
        IntArray parsed;
        // Actual file bytes
        byte[] data;

        CSV() {
            rows = new IntArray(2*1024*1024);
            parsed = new IntArray(2*1024*1024);
        }

        void parse(byte data[]) {
            this.data = data;
            rows.reset();
            parsed.reset();

            // for each line
            int i = 0;
            while (i < data.length) {
                rows.put(parsed.cnt);
                parsed.put(i);

                do {
                    byte c = data[i++];
                    if (c == '\r' || c == '\n') {
                        // line break (CRLF included)
                        if (i < data.length && c + data[i] == '\r' + '\n') {
                            i += 1;
                        }
                        break;
                    } else if (c == ',') {
                        parsed.put(i);
                    } else if (c == '"') {
                        while (data[i++] != '"') {}
                    }
                } while (i < data.length);
            }

            // write out EOF
            rows.put(parsed.cnt);
            parsed.put(data.length);
        }

        int row_len(int i) { return rows.get(i + 1) - rows.get(i); }
        String entry(int i, int j) {
            int k     = rows.get(i);
            int start = parsed.get(k+j);
            int end   = parsed.get(k+j+1) - 1;
            return new String(data, start, end - start, StandardCharsets.UTF_8);
        }
    };

    public static void main(String[] args) throws IOException {
        if (args[0].equals("-single")) {
            // single test
            byte[] data = Files.readAllBytes(Paths.get(args[1]));
            var csv = new CSV();
            csv.parse(data);
            System.out.println(csv.entry(csv.rows.cnt - 2, 2));
        } else {
            byte[] data = Files.readAllBytes(Paths.get(args[0]));
            var csv = new CSV();

            long avg = 0;
            for (int i = 0; i < 10; i++) {
                long start = System.nanoTime();
                csv.parse(data);
                long elapsed = System.nanoTime() - start;
                avg += elapsed / 10;

                double sec = elapsed / 1000000000.0;
                double bw = (double) data.length / sec;
                bw /= 1048576.0f;

                System.out.printf("Run %d: %f MB/s (avg %f seconds)\n", 1+i, bw, sec, csv.entry(csv.rows.cnt - 2, 2));
            }

            double sec = avg / 1000000000.0;
            double bw = ((double) data.length / sec);
            bw /= 1048576.0f;

            System.out.printf("Average nanos: %f MB/s (avg %f seconds)", bw, sec);
        }
    }
}