Epsilon GC + a number of other small tweaks (#513)

* Version 3

* Use SWAR algorithm from netty for finding a symbol in a string

* Faster equals - store the remainder in a long field (- 0.5s)

* optimise parsing numbers - prep

* Keep tweaking parsing logic

* Rewrote number parsing

may be a tiby bit faster it at all

* Epsilon GC

calculate_average_roman-r-m.sh

@@ -16,4 +16,10 @@
 #
 
 JAVA_OPTS="--enable-preview -XX:+UseTransparentHugePages"
+
+# epsilon GC needs enough memory or it makes things worse
+# see https://stackoverflow.com/questions/58087596/why-are-repeated-memory-allocations-observed-to-be-slower-using-epsilon-vs-g1
+# 2GB seems to be the sweet spot
+JAVA_OPTS="$JAVA_OPTS -XX:+UnlockExperimentalVMOptions -XX:-EnableJVMCI -XX:+UseEpsilonGC -Xmx2G -Xms2G -XX:+AlwaysPreTouch"
+
 java $JAVA_OPTS --class-path target/average-1.0.0-SNAPSHOT.jar dev.morling.onebrc.CalculateAverage_roman_r_m

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

@@ -33,37 +33,35 @@ public class CalculateAverage_roman_r_m {
 
     private static Unsafe UNSAFE;
 
-    // based on http://0x80.pl/notesen/2023-03-06-swar-find-any.html
+    private static long broadcast(byte b) {
-    static long hasZeroByte(long l) {
-        return ((l - 0x0101010101010101L) & ~(l) & 0x8080808080808080L);
-    }
-
-    static long firstSetByteIndex(long l) {
-        return ((((l - 1) & 0x101010101010101L) * 0x101010101010101L) >> 56) - 1;
-    }
-
-    static long broadcast(byte b) {
         return 0x101010101010101L * b;
     }
 
-    static long SEMICOLON_MASK = broadcast((byte) ';');
+    private static final long SEMICOLON_MASK = broadcast((byte) ';');
-    static long LINE_END_MASK = broadcast((byte) '\n');
+    private static final long LINE_END_MASK = broadcast((byte) '\n');
+    private static final long DOT_MASK = broadcast((byte) '.');
 
-    static long find(long l, long mask) {
+    // from netty
-        long xor = l ^ mask;
+
-        long match = hasZeroByte(xor);
+    /**
-        return match != 0 ? firstSetByteIndex(match) : -1;
+     * Applies a compiled pattern to given word.
+     * Returns a word where each byte that matches the pattern has the highest bit set.
+     */
+    private static long applyPattern(final long word, final long pattern) {
+        long input = word ^ pattern;
+        long tmp = (input & 0x7F7F7F7F7F7F7F7FL) + 0x7F7F7F7F7F7F7F7FL;
+        return ~(tmp | input | 0x7F7F7F7F7F7F7F7FL);
     }
 
     static long nextNewline(long from, MemorySegment ms) {
         long start = from;
         long i;
         long next = ms.get(ValueLayout.JAVA_LONG_UNALIGNED, start);
-        while ((i = find(next, LINE_END_MASK)) < 0) {
+        while ((i = applyPattern(next, LINE_END_MASK)) == 0) {
             start += 8;
             next = ms.get(ValueLayout.JAVA_LONG_UNALIGNED, start);
         }
-        return start + i;
+        return start + Long.numberOfTrailingZeros(i) / 8;
     }
 
     static class Worker {
@@ -84,55 +82,53 @@ public class CalculateAverage_roman_r_m {
 
         private void parseName(ByteString station) {
             long start = offset;
-            long pos = -1;
+            long pattern;
-
-            while (end - offset > 8) {
             long next = UNSAFE.getLong(offset);
-                pos = find(next, SEMICOLON_MASK);
+            while ((pattern = applyPattern(next, SEMICOLON_MASK)) == 0) {
-                if (pos >= 0) {
-                    offset += pos;
-                    break;
-                }
-                else {
                 offset += 8;
+                next = UNSAFE.getLong(offset);
             }
-            }
+            int bytes = Long.numberOfTrailingZeros(pattern) / 8;
-            if (pos < 0) {
+            offset += bytes;
-                while (UNSAFE.getByte(offset++) != ';') {
-                }
-                offset--;
-            }
 
             int len = (int) (offset - start);
             station.offset = start;
             station.len = len;
             station.hash = 0;
+            station.tail = next & ((1L << (8 * bytes)) - 1);
 
             offset++;
         }
 
-        long parseNumberFast() {
+        int parseNumberFast() {
             long encodedVal = UNSAFE.getLong(offset);
 
-            var len = find(encodedVal, LINE_END_MASK);
+            int neg = 1 - Integer.bitCount((int) (encodedVal & 0x10));
-            offset += len + 1;
+            encodedVal >>>= 8 * neg;
+
+            var len = applyPattern(encodedVal, DOT_MASK);
+            len = Long.numberOfTrailingZeros(len) / 8;
 
             encodedVal ^= broadcast((byte) 0x30);
 
-            long c0 = len == 4 ? 100 : 10;
+            int intPart = (int) (encodedVal & ((1 << (8 * len)) - 1));
-            long c1 = 10 * (len - 3);
+            intPart <<= 8 * (2 - len);
-            long c2 = 4 - len;
+            intPart *= (100 * 256 + 10);
-            long c3 = len - 3;
+            intPart = (intPart & 0x3FF80) >>> 8;
-            long a = (encodedVal & 0xFF) * c0;
-            long b = ((encodedVal & 0xFF00) >>> 8) * c1;
-            long c = ((encodedVal & 0xFF0000L) >>> 16) * c2;
-            long d = ((encodedVal & 0xFF000000L) >>> 24) * c3;
 
-            return a + b + c + d;
+            int frac = (int) ((encodedVal >>> (8 * (len + 1))) & 0xFF);
+
+            offset += neg + len + 3; // 1 for . + 1 for fractional part + 1 for new line char
+            int sign = 1 - 2 * neg;
+            int val = intPart + frac;
+            return sign * val;
         }
 
-        long parseNumberSlow() {
+        int parseNumberSlow() {
-            long val = UNSAFE.getByte(offset++) - '0';
+            int neg = 1 - Integer.bitCount(UNSAFE.getByte(offset) & 0x10);
+            offset += neg;
+
+            int val = UNSAFE.getByte(offset++) - '0';
             byte b;
             while ((b = UNSAFE.getByte(offset++)) != '.') {
                 val = val * 10 + (b - '0');
@@ -140,24 +136,19 @@ public class CalculateAverage_roman_r_m {
             b = UNSAFE.getByte(offset);
             val = val * 10 + (b - '0');
             offset += 2;
-            return val;
-        }
-
-        long parseNumber() {
-            long val;
-            int neg = 1 - Integer.bitCount(UNSAFE.getByte(offset) & 0x10);
-            offset += neg;
-
-            if (end - offset > 8) {
-                val = parseNumberFast();
-            }
-            else {
-                val = parseNumberSlow();
-            }
             val *= 1 - 2 * neg;
             return val;
         }
 
+        int parseNumber() {
+            if (end - offset >= 8) {
+                return parseNumberFast();
+            }
+            else {
+                return parseNumberSlow();
+            }
+        }
+
         public TreeMap<String, ResultRow> run() {
             var resultStore = new ResultStore();
             var station = new ByteString(ms);
@@ -218,6 +209,7 @@ public class CalculateAverage_roman_r_m {
         private long offset;
         private int len = 0;
         private int hash = 0;
+        private long tail = 0L;
 
         ByteString(MemorySegment ms) {
             this.ms = ms;
@@ -235,6 +227,7 @@ public class CalculateAverage_roman_r_m {
             copy.offset = this.offset;
             copy.len = this.len;
             copy.hash = this.hash;
+            copy.tail = this.tail;
             return copy;
         }
 
@@ -259,19 +252,7 @@ public class CalculateAverage_roman_r_m {
                     return false;
                 }
             }
-            if (len >= 8) {
+            return this.tail == that.tail;
-                long l1 = UNSAFE.getLong(offset + len - 8);
-                long l2 = UNSAFE.getLong(that.offset + len - 8);
-                return l1 == l2;
-            }
-            for (; i < len; i++) {
-                byte i1 = UNSAFE.getByte(offset + i);
-                byte i2 = UNSAFE.getByte(that.offset + i);
-                if (i1 != i2) {
-                    return false;
-                }
-            }
-            return true;
         }
 
         @Override