From 61819966783db7f36c5e7a89edaff05052392381 Mon Sep 17 00:00:00 2001 From: Jason Nochlin <91577+hundredwatt@users.noreply.github.com> Date: Fri, 12 Jan 2024 01:03:31 -0700 Subject: hundredwatt - 2nd submission (#338) * check full hash before comparing * implement merykitty suggestions to simplify temperature masking; required refactoring to little-endian * standalone script for offline Perfect Hash seed searching * stop using an oversized hash table --------- Co-authored-by: Jason Nochlin --- .../onebrc/CalculateAverage_hundredwatt.java | 71 ++++++++-------------- 1 file changed, 25 insertions(+), 46 deletions(-) (limited to 'src/main/java/dev/morling/onebrc/CalculateAverage_hundredwatt.java') diff --git a/src/main/java/dev/morling/onebrc/CalculateAverage_hundredwatt.java b/src/main/java/dev/morling/onebrc/CalculateAverage_hundredwatt.java index 051de9c..9d935ff 100644 --- a/src/main/java/dev/morling/onebrc/CalculateAverage_hundredwatt.java +++ b/src/main/java/dev/morling/onebrc/CalculateAverage_hundredwatt.java @@ -17,6 +17,7 @@ package dev.morling.onebrc; import java.io.IOException; import java.nio.ByteBuffer; +import java.nio.ByteOrder; import java.nio.MappedByteBuffer; import java.nio.channels.FileChannel; import java.nio.file.Files; @@ -36,7 +37,7 @@ public class CalculateAverage_hundredwatt { private static final long FILE_CHUNK_SIZE = CHUNK_SIZE - MAX_ROW_SIZE; public static final int TEMPERATURE_SLOTS = 5003; // prime number private static final short[] TEMPERATURES = new short[TEMPERATURE_SLOTS]; - private static final long PERFECT_HASH_SEED = -5353381455852817461L; + private static final long PERFECT_HASH_SEED = -1982870890352534081L; // Construct a perfect hash function mapping temperatures encoded as longs (e.g., 0x2d342e3000000000 for -4.3) to // the corresponding short integer (e.g., -43). @@ -46,17 +47,17 @@ public class CalculateAverage_hundredwatt { Map decodeTemperatureMap = new HashMap<>(); for (short i = -999; i <= 999; i++) { long word = 0; - int shift = 56; + int shift = 0; if (i < 0) { word |= ((long) '-') << shift; - shift -= 8; + shift += 8; } if (Math.abs(i) >= 100) { int hh = Math.abs(i) / 100; int tt = (Math.abs(i) - hh * 100) / 10; word |= ((long) (hh + '0')) << shift; - shift -= 8; + shift += 8; word |= ((long) (tt + '0')) << shift; } else { @@ -64,9 +65,9 @@ public class CalculateAverage_hundredwatt { // convert to ascii word |= ((long) (tt + '0')) << shift; } - shift -= 8; + shift += 8; word |= ((long) '.') << shift; - shift -= 8; + shift += 8; int uu = Math.abs(i) % 10; word |= ((long) (uu + '0')) << shift; @@ -74,31 +75,6 @@ public class CalculateAverage_hundredwatt { decodeTemperatureMap.put(word, i); } - // Brute force to find seed: - // Random rand = new Random(System.nanoTime()); - // int max = 0; - // int attempts = 0; - // while (true) { - // BitSet bs = new BitSet(5003); - // var seed = rand.nextLong(); - // seed |= 0b1; // make sure it's odd - // for (var word : decodeTemperatureMap.keySet()) { - // var h = (word * seed) & ~(1L << 63); - // var pos = (int) (h % 5003); - // bs.set(pos); - // } - // ; - // var c = bs.cardinality(); - // if (c == decodeTemperatureMap.size()) { - // System.out.println("seed: " + seed + " cardinality: " + c + " max cardinality: " + max); - // break; - // } - // max = Math.max(max, c); - // if (attempts % 100_000 == 0) - // System.out.println("seed: " + seed + " cardinality: " + c + " max cardinality: " + max); - // attempts++; - // } - decodeTemperatureMap.entrySet().stream().forEach(e -> { var word = e.getKey(); var h = (word * PERFECT_HASH_SEED) & ~(1L << 63); @@ -144,11 +120,12 @@ public class CalculateAverage_hundredwatt { } static class HashTable { - private static final int INITIAL_SIZE = 128 * 1024; + private static final int INITIAL_SIZE = 16 * 1024; private static final float LOAD_FACTOR = 0.75f; private static final int GROW_FACTOR = 4; private final long[][] KEYS = new long[INITIAL_SIZE][]; private final Record[] VALUES = new Record[INITIAL_SIZE]; + private final long[] HASHES = new long[INITIAL_SIZE]; private int size = INITIAL_SIZE; public HashTable() { @@ -162,13 +139,14 @@ public class CalculateAverage_hundredwatt { // linear probing int i = 0; - while (KEYS[idx] != null && (0 != Arrays.compareUnsigned(KEYS[idx], 0, KEYS[idx].length, key, 0, length))) { + while (KEYS[idx] != null && (HASHES[idx] != hash) && (0 != Arrays.compareUnsigned(KEYS[idx], 0, KEYS[idx].length, key, 0, length))) { i++; idx = (idx + 1) & (size - 1); } if (KEYS[idx] == null) { KEYS[idx] = Arrays.copyOf(key, length); + HASHES[idx] = hash; } VALUES[idx].updateWith(value); @@ -186,7 +164,7 @@ public class CalculateAverage_hundredwatt { } private static String keyToString(long[] key) { - ByteBuffer kb = ByteBuffer.allocate(8 * key.length); + ByteBuffer kb = ByteBuffer.allocate(8 * key.length).order(ByteOrder.LITTLE_ENDIAN); Arrays.stream(key).forEach(kb::putLong); // remove trailing '\0' bytes from kb and @@ -194,7 +172,7 @@ public class CalculateAverage_hundredwatt { byte b; int limit = kb.position() - 8; kb.position(limit); - while ((b = kb.get()) != 0 && b != ';') { + while ((b = kb.get()) != 0 && b != ';' && limit < kb.capacity() - 1) { limit++; } @@ -202,7 +180,7 @@ public class CalculateAverage_hundredwatt { byte[] bytes = new byte[limit]; kb.get(bytes); - return new String(bytes).replace("\0", ""); + return new String(bytes); } private static Record merge(Record v, Record value) { @@ -215,6 +193,7 @@ public class CalculateAverage_hundredwatt { } private static int processChunk(ByteBuffer bb, HashTable hashTable, long start, long size) { + bb.order(ByteOrder.LITTLE_ENDIAN); // Find first entry while (start != 0 && bb.get() != '\n') { } @@ -228,6 +207,7 @@ public class CalculateAverage_hundredwatt { long temperature_hash; int temperature_pos; short temperature_value; + int hashInt; int i = 0; int end = (int) (size - MAX_ROW_SIZE); @@ -258,29 +238,28 @@ public class CalculateAverage_hundredwatt { hasvalue = (op1 & op2 & 0x8080808080808080L); } hash ^= key[offset]; // unset last word since it will be updated - key[offset] = key[offset] & (-hasvalue); // ';' == 0x3b and -hasvalue is something like 0xff8000..., we can ignore the 0x80 byte since 0x3b & 0x80 == 0 + key[offset] = key[offset] & ~(-(hasvalue >> 7)); hash ^= key[offset]; - position = position + offset * 8 + (Long.numberOfLeadingZeros(hasvalue)) / 8 + 1; // +1 for \n + position = position + offset * 8 + Long.numberOfTrailingZeros(hasvalue) / 8 + 1; // +1 for \n // Parse temperature word = bb.getLong(position); - arg = (word) ^ 0x0101010101010101L * ('\n'); - op1 = (arg - 0x0101010101010101L); - op2 = ~(arg); - hasvalue = (op1 & op2 & 0x8080808080808080L); - word = word & ((-hasvalue)); + hasvalue = (word - 0x0B0B0B0B0B0B0B0BL) & 0x8080808080808080L; + int newlinePos = Long.numberOfTrailingZeros(hasvalue) - 8; + + word = word & (~(-(1L << newlinePos))); // Perfect hash lookup for temperature temperature_hash = (word * PERFECT_HASH_SEED) & ~(1L << 63); temperature_pos = (int) (temperature_hash % TEMPERATURE_SLOTS); temperature_value = TEMPERATURES[temperature_pos]; - position = position + (Long.numberOfLeadingZeros(hasvalue)) / 8 + 1; // +1 for \n + position = position + newlinePos / 8 + 2; // +1 for \n - int hash2 = (int) (hash ^ (hash >> 32)); + hashInt = (int) (hash ^ (hash >> 32)); - hashTable.putOrMerge(hash2, offset + 1, key, temperature_value); + hashTable.putOrMerge(hashInt, offset + 1, key, temperature_value); } return i; } -- cgit v1.2.3