RealNeGate · November 27, 2023 11:41 · Nov 27, 2023 · Nov 25, 2023
diff --git a/csv.java b/csv.java
@@ -60,8 +60,7 @@ void parse(byte data[]) {
                     } else if (c == ',') {
                         parsed.put(i);
                     } else if (c == '"') {
-                        while (data[i] != '"') { i++; }
-                        i += 1;
+                        while (data[i++] != '"') {}
                     }
                 } while (i < data.length);
             }

diff --git a/csv.java b/csv.java
@@ -0,0 +1,115 @@
+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] != '"') { i++; }
+                        i += 1;
+                    }
+                } 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);
+        }
+    }
+}