1brc contribution from mattiz (first attempt) (#567)

* Contribution from mattiz

* Formatted code

calculate_average_mattiz.sh

@@ -0,0 +1,19 @@
+#!/bin/sh
+#
+#  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.
+#
+
+JAVA_OPTS=""
+java $JAVA_OPTS --class-path target/average-1.0.0-SNAPSHOT.jar dev.morling.onebrc.CalculateAverage_mattiz

src/main/java/dev/morling/onebrc/CalculateAverage_mattiz.java

@@ -0,0 +1,324 @@
+/*
+ *  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.*;
+import java.nio.ByteBuffer;
+import java.nio.MappedByteBuffer;
+import java.nio.channels.FileChannel;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.nio.file.StandardOpenOption;
+import java.util.*;
+import static java.nio.channels.FileChannel.MapMode.READ_ONLY;
+
+public class CalculateAverage_mattiz {
+    private static final int TWO_BYTE_TO_INT = 480 + 48; // 48 is the ASCII code for '0'
+    private static final int THREE_BYTE_TO_INT = 4800 + 480 + 48;
+    private static final String FILE = "./measurements.txt";
+    public static final int PARTS = 8;
+
+    public static void main(String[] args) throws Exception {
+        var result = new CalculateAverage_mattiz().calculate(FILE, PARTS);
+        System.out.println(result);
+    }
+
+    StationList calculate(String file, int numParts) throws Exception {
+        var buffers = createBuffers(Paths.get(file), numParts);
+
+        return buffers
+                .parallelStream()
+                .map(this::aggregate)
+                .reduce(StationList::merge)
+                .orElseThrow();
+    }
+
+    record BufferAndSize(ByteBuffer buffer, long size) {
+    }
+
+    List<ByteBuffer> createBuffers(Path file, int numParts) throws IOException {
+        FileChannel fileChannel = FileChannel.open(file, StandardOpenOption.READ);
+
+        var fileSize = fileChannel.size();
+
+        if (fileSize < (1024 * 1024)) { // Only one core for small files
+            numParts = 1;
+        }
+
+        var chunkSize = fileSize / numParts;
+        var buffers = new ArrayList<ByteBuffer>();
+        long filePointer = 0;
+
+        for (int i = 0; i < numParts; i++) {
+            if (i != numParts - 1) { // not last element
+                var adjustedChunkSize = getBuffer(fileChannel, filePointer, chunkSize, true);
+                buffers.add(adjustedChunkSize.buffer());
+                filePointer += adjustedChunkSize.size();
+            }
+            else {
+                var adjustedChunkSize = getBuffer(fileChannel, filePointer, fileSize - filePointer, false);
+                buffers.add(adjustedChunkSize.buffer());
+            }
+        }
+
+        return buffers;
+    }
+
+    BufferAndSize getBuffer(FileChannel fileChannel, long start, long size, boolean adjust) throws IOException {
+        MappedByteBuffer buffer = fileChannel.map(READ_ONLY, start, size);
+
+        var actualSize = ((int) size);
+
+        if (adjust) {
+            while (buffer.get(actualSize - 1) != '\n') {
+                actualSize--;
+            }
+        }
+
+        buffer.limit(actualSize);
+
+        return new BufferAndSize(buffer, actualSize);
+    }
+
+    private StationList aggregate(ByteBuffer buffer) {
+        var measurements = new StationList();
+
+        while (buffer.hasRemaining()) {
+            int startPos = buffer.position();
+
+            byte b;
+            int hash = 0;
+            while ((b = buffer.get()) != ';') {
+                hash = ((hash << 5) - hash) + b;
+            }
+
+            if (hash < 0) {
+                hash = -hash;
+            }
+
+            int length = buffer.position() - startPos - 1;
+            byte[] station = new byte[length];
+            buffer.get(startPos, station);
+
+            int value = readValue(buffer);
+
+            measurements.update(station, length, hash, value);
+        }
+
+        return measurements;
+    }
+
+    /*
+     * Read decimal number from ascii characters (copied from arjenw)
+     *
+     * Example:
+     * If you have the decimal number 1.4,
+     * then byte 1 contain 49 (ascii code for '1')
+     * and byte 3 contain 52 (ascii code for '4')
+     * Subtract 480 + 48 (48 is the ASCII code for '0')
+     * to move number from ascii number to int
+     *
+     * 49 * 10 + 52 - 528 = 14
+     */
+    private static int readValue(ByteBuffer buffer) {
+        int value;
+        byte b1 = buffer.get();
+        byte b2 = buffer.get();
+        byte b3 = buffer.get();
+        byte b4 = buffer.get();
+
+        if (b2 == '.') {// value is n.n
+            value = (b1 * 10 + b3 - TWO_BYTE_TO_INT);
+        }
+        else {
+            if (b4 == '.') { // value is -nn.n
+                value = -(b2 * 100 + b3 * 10 + buffer.get() - THREE_BYTE_TO_INT);
+            }
+            else if (b1 == '-') { // value is -n.n
+                value = -(b2 * 10 + b4 - TWO_BYTE_TO_INT);
+            }
+            else { // value is nn.n
+                value = (b1 * 100 + b2 * 10 + b4 - THREE_BYTE_TO_INT);
+            }
+            buffer.get(); // new line
+        }
+        return value;
+    }
+}
+
+class CustomMap {
+    private static final int SIZE = 1024 * 64;
+    private final Station[] stationList = new Station[SIZE];
+
+    public void addOrUpdate(byte[] stationName, int length, int hash, int value) {
+        int slot = hash & (SIZE - 1);
+        var station = stationList[slot];
+
+        while (station != null
+                && station.getHash() != hash
+                && !Arrays.equals(
+                        station.getName(), 0, station.getName().length,
+                        stationName, 0, length)) {
+
+            slot = (slot + 1) & (SIZE - 1);
+            station = stationList[slot];
+        }
+
+        if (station == null) {
+            stationList[slot] = new Station(stationName, hash);
+        }
+
+        stationList[slot].add(value);
+    }
+
+    public Station get(byte[] stationName) {
+        return stationList[findSlot(stationName)];
+    }
+
+    public void put(byte[] stationName, Station newStation) {
+        stationList[findSlot(stationName)] = newStation;
+    }
+
+    private int findSlot(byte[] stationName) {
+        int hash = getHash(stationName);
+        int slot = hash & (SIZE - 1);
+        var station = stationList[slot];
+
+        while (station != null
+                && station.getHash() != hash
+                && !Arrays.equals(station.getName(), stationName)) {
+
+            slot = (slot + 1) & (SIZE - 1);
+            station = stationList[slot];
+        }
+
+        return slot;
+    }
+
+    private int getHash(byte[] key) {
+        int hash = 0;
+
+        for (byte b : key) {
+            hash = hash * 31 + b;
+        }
+
+        if (hash < 0) {
+            hash = -hash;
+        }
+
+        return hash;
+    }
+
+    public Set<Map.Entry<byte[], Station>> entrySet() {
+        var sorted = new HashMap<byte[], Station>();
+
+        for (var s : stationList) {
+            if (s != null) {
+                sorted.put(s.getName(), s);
+            }
+        }
+
+        return sorted.entrySet();
+    }
+
+    public Map<String, Station> sorted() {
+        var sorted = new TreeMap<String, Station>();
+
+        for (var s : stationList) {
+            if (s != null) {
+                sorted.put(new String(s.getName(), StandardCharsets.UTF_8), s);
+            }
+        }
+
+        return sorted;
+    }
+}
+
+class StationList {
+    private final CustomMap stations = new CustomMap();
+
+    public void update(byte[] stationName, int length, int hash, int value) {
+        stations.addOrUpdate(stationName, length, hash, value);
+    }
+
+    public StationList merge(StationList other) {
+        for (var aggregator : other.stations.entrySet()) {
+            var agg = stations.get(aggregator.getKey());
+
+            if (agg == null) {
+                stations.put(aggregator.getKey(), aggregator.getValue());
+            }
+            else {
+                agg.merge(aggregator.getValue());
+            }
+        }
+
+        return this;
+    }
+
+    @Override
+    public String toString() {
+        return stations.sorted().toString();
+    }
+}
+
+class Station {
+    private final byte[] name;
+    private final int hash;
+    private int min = Integer.MAX_VALUE;
+    private int max = Integer.MIN_VALUE;
+    private int sum;
+    private int count;
+
+    public Station(byte[] name, int hash) {
+        this.name = name;
+        this.hash = hash;
+    }
+
+    public void add(int max, int min, int sum, int count) {
+        this.max = Math.max(this.max, max);
+        this.min = Math.min(this.min, min);
+        this.sum += sum;
+        this.count += count;
+    }
+
+    public void add(int value) {
+        this.max = Math.max(this.max, value);
+        this.min = Math.min(this.min, value);
+        this.sum += value;
+        this.count++;
+    }
+
+    public void merge(Station other) {
+        this.max = Math.max(this.max, other.max);
+        this.min = Math.min(this.min, other.min);
+        this.sum += other.sum;
+        this.count += other.count;
+    }
+
+    public String toString() {
+        return (min / 10.0) + "/" + (Math.round(((double) sum) / count)) / 10.0 + "/" + (max / 10.0);
+    }
+
+    public byte[] getName() {
+        return name;
+    }
+
+    public int getHash() {
+        return hash;
+    }
+}