Resolves #102 and Code Optimizations

1 files changed, 106 insertions, 44 deletions

diff --git a/src/main/java/dev/morling/onebrc/CalculateAverage_kuduwa_keshavram.java b/src/main/java/dev/morling/onebrc/CalculateAverage_kuduwa_keshavram.java
index 49c77c0..d9da874 100644
--- a/src/main/java/dev/morling/onebrc/CalculateAverage_kuduwa_keshavram.java
+++ b/src/main/java/dev/morling/onebrc/CalculateAverage_kuduwa_keshavram.java
@@ -18,62 +18,124 @@ package dev.morling.onebrc;
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.util.DoubleSummaryStatistics;
 import java.util.Map;
-import java.util.concurrent.ConcurrentHashMap;
+import java.util.function.Function;
+import java.util.function.ToDoubleFunction;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 public class CalculateAverage_kuduwa_keshavram {
 
     private static final String FILE = "./measurements.txt";
+    private static final Function<String, String> KEY_MAPPER = line -> {
+        int pivot = line.indexOf(";");
+        return line.substring(0, pivot);
+    };
+    private static final ToDoubleFunction<String> VALUE_MAPPER = line -> {
+        int pivot = line.indexOf(";");
+        return toDouble(line.substring(pivot + 1));
+    };
 
-  private record Measurement(double min, double max, double sum, long count) {
-
-    Measurement(double initialMeasurement) {
-      this(initialMeasurement, initialMeasurement, initialMeasurement, 1);
+    public static void main(String[] args) throws IOException, InterruptedException {
+        try (Stream<String> lines = Files.lines(Path.of(FILE))) {
+            Map<String, DoubleSummaryStatistics> resultMap = lines
+                    .parallel()
+                    .collect(
+                            Collectors.groupingBy(KEY_MAPPER, Collectors.summarizingDouble(VALUE_MAPPER)));
+            System.out.println(
+                    resultMap.entrySet().stream()
+                            .sorted(Map.Entry.comparingByKey())
+                            .map(
+                                    entry -> String.format(
+                                            "%s=%.1f/%.1f/%.1f",
+                                            entry.getKey(),
+                                            entry.getValue().getMin(),
+                                            entry.getValue().getAverage(),
+                                            entry.getValue().getMax()))
+                            .collect(Collectors.joining(", ", "{", "}")));
+        }
     }
 
-    public static Measurement combineWith(Measurement m1, Measurement m2) {
-      return new Measurement(
-          m1.min < m2.min ? m1.min : m2.min,
-          m1.max > m2.max ? m1.max : m2.max,
-          m1.sum + m2.sum,
-          m1.count + m2.count);
-    }
+    private static final long MAX_VALUE_DIVIDE_10 = Long.MAX_VALUE / 10;
 
-    public String toString() {
-      return round(min) + "/" + round(sum / count) + "/" + round(max);
-    }
+    private static double toDouble(String num) {
+        long value = 0;
+        int exp = 0;
+        boolean negative = false;
+        int decimalPlaces = Integer.MIN_VALUE;
+        for (byte ch : num.getBytes()) {
+            if (ch >= '0' && ch <= '9') {
+                value = value * 10 + (ch - '0');
+                decimalPlaces++;
+            }
+            else if (ch == '-') {
+                negative = true;
+            }
+            else if (ch == '.') {
+                decimalPlaces = 0;
+            }
+            else {
+                break;
+            }
+        }
 
-    private double round(double value) {
-      return Math.round(value * 10.0) / 10.0;
+        return asDouble(value, exp, negative, decimalPlaces);
     }
-  }
 
-    public static void main(String[] args) throws IOException {
-        // long before = System.currentTimeMillis();
-        Map<String, Measurement> resultMap = new ConcurrentHashMap<>();
-        Files.lines(Path.of(FILE))
-                .parallel()
-                .forEach(
-                        line -> {
-                            int pivot = line.indexOf(";");
-                            String key = line.substring(0, pivot);
-                            Measurement measured = new Measurement(Double.parseDouble(line.substring(pivot + 1)));
-                            Measurement existingMeasurement = resultMap.get(key);
-                            if (existingMeasurement != null) {
-                                resultMap.put(key, Measurement.combineWith(existingMeasurement, measured));
-                            }
-                            else {
-                                resultMap.put(key, measured);
-                            }
-                        });
-        System.out.print("{");
-        System.out.print(
-                resultMap.entrySet().stream()
-                        .map(Object::toString)
-                        .sorted()
-                        .collect(Collectors.joining(", ")));
-        System.out.println("}");
-        // System.out.println("Took: " + (System.currentTimeMillis() - before));
+    private static double asDouble(long value, int exp, boolean negative, int decimalPlaces) {
+        if (decimalPlaces > 0 && value < Long.MAX_VALUE / 2) {
+            if (value < Long.MAX_VALUE / (1L << 32)) {
+                exp -= 32;
+                value <<= 32;
+            }
+            if (value < Long.MAX_VALUE / (1L << 16)) {
+                exp -= 16;
+                value <<= 16;
+            }
+            if (value < Long.MAX_VALUE / (1L << 8)) {
+                exp -= 8;
+                value <<= 8;
+            }
+            if (value < Long.MAX_VALUE / (1L << 4)) {
+                exp -= 4;
+                value <<= 4;
+            }
+            if (value < Long.MAX_VALUE / (1L << 2)) {
+                exp -= 2;
+                value <<= 2;
+            }
+            if (value < Long.MAX_VALUE / (1L << 1)) {
+                exp -= 1;
+                value <<= 1;
+            }
+        }
+        for (; decimalPlaces > 0; decimalPlaces--) {
+            exp--;
+            long mod = value % 5;
+            value /= 5;
+            int modDiv = 1;
+            if (value < Long.MAX_VALUE / (1L << 4)) {
+                exp -= 4;
+                value <<= 4;
+                modDiv <<= 4;
+            }
+            if (value < Long.MAX_VALUE / (1L << 2)) {
+                exp -= 2;
+                value <<= 2;
+                modDiv <<= 2;
+            }
+            if (value < Long.MAX_VALUE / (1L << 1)) {
+                exp -= 1;
+                value <<= 1;
+                modDiv <<= 1;
+            }
+            if (decimalPlaces > 1)
+                value += modDiv * mod / 5;
+            else
+                value += (modDiv * mod + 4) / 5;
+        }
+        final double d = Math.scalb((double) value, exp);
+        return negative ? -d : d;
     }
 }