1 files changed, 131 insertions, 0 deletions
diff --git a/src/main/java/dev/morling/onebrc/CalculateAverage_ddimtirov.java b/src/main/java/dev/morling/onebrc/CalculateAverage_ddimtirov.java
new file mode 100644
index 0000000..285ab00
--- /dev/null
+++ b/src/main/java/dev/morling/onebrc/CalculateAverage_ddimtirov.java
@@ -0,0 +1,131 @@
+/*
+ *  Copyright 2023 The original authors
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package dev.morling.onebrc;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.TreeMap;
+import java.util.stream.Collector;
+
+import static java.util.stream.Collectors.groupingByConcurrent;
+
+// gunnar morling - 2:10
+// roy van rijn -   1:01
+//                  0:53
+
+public class CalculateAverage_ddimtirov {
+    public record InputLine(String station, int value) {
+
+        public static InputLine fromLine(String line) {
+            int endOfText = line.indexOf(";");
+
+            String station = line.substring(0, endOfText);
+
+            int startOfWhole = endOfText + 1;
+            int sign;
+            if (line.charAt(startOfWhole) == '-') {
+                sign = -1;
+                startOfWhole++;
+            } else {
+                sign = 1;
+            }
+
+            int endOfWhole = line.lastIndexOf(".");
+            var whole = unsafeParsePositiveInt(line, startOfWhole, endOfWhole);
+            var decimal = unsafeParsePositiveInt(line,endOfWhole+1, line.length());
+            int fixpoint10 = (whole * 10  + decimal) * sign;
+
+            return new InputLine(station, fixpoint10);
+        }
+
+        static int unsafeParsePositiveInt(String s, int start, int end) {
+            int acc = 0;
+            for (int i = start; i<end; i++) {
+                if (acc != 0) acc *= 10;
+                char c = s.charAt(i);
+                var v = c - '0';
+                assert v>=0 && v<=9 : String.format("Character '%s', value %,d", c, v);
+                acc += v;
+            }
+            return acc;
+        }
+    }
+
+    private static class OutputMetrics {
+        private int min = Integer.MAX_VALUE;
+        private int max = Integer.MIN_VALUE;
+        private long sum;
+        private long count;
+
+        @SuppressWarnings("ManualMinMaxCalculation")
+        public OutputMetrics combine(OutputMetrics o) {
+            var r = new OutputMetrics();
+            r.min = min < o.min ? min : o.min;
+            r.max = max > o.max ? max : o.max;
+            r.sum = sum + o.sum;
+            r.count = count + o.count;
+            return r;
+        }
+
+        public void accumulate(InputLine m) {
+            if (m.value < min) min = m.value;
+            if (m.value > max) max = m.value;
+            sum += m.value;
+            count++;
+        }
+
+        @Override
+        public String toString() {
+            var min = this.min / 10.0;
+            var mean = Math.round(this.sum / (double) count) / 10.0;
+            var max = this.max / 10.0;
+            return min + "/" + mean + "/" + max;
+        }
+    }
+
+    public static void main(String[] args) throws IOException {
+//         var start = Instant.now();
+        Instant start = null;
+        var path = Path.of("./measurements.txt");
+        var buffer = 8192 * 20;
+
+        // Files.lines() is optimized for files that can be indexed by int
+        // For larger files it falls back to buffered reader, which we now
+        // use directly to be able to tweak the buffer size.
+        try (var reader = new BufferedReader(new InputStreamReader(Files.newInputStream(path)), buffer)) {
+            var stationsToMetrics = reader.lines()
+                    .map(InputLine::fromLine)
+                    .parallel()
+                    .collect(groupingByConcurrent(InputLine::station, Collector.of(
+                            OutputMetrics::new,
+                            OutputMetrics::accumulate,
+                            OutputMetrics::combine,
+                            OutputMetrics::toString
+                    )));
+            System.out.println(new TreeMap<>(stationsToMetrics));
+            assert Files.readAllLines(Path.of("expected_result.txt")).getFirst().equals(new TreeMap<>(stationsToMetrics).toString());
+        }
+
+        //noinspection ConstantValue
+        if (start!=null) System.err.println(Duration.between(start, Instant.now()));
+    }
+
+}