Second tuning for thomaswue
* Optimize checking for collisions by doing this a long at a time always. * Use a long at a time scanning for delimiter. * Minor tuning. Now below 0.80s on Intel i9-13900K. * Add number parsing code from Quan Anh Mai. Fix name length issue. * Include suggestion from Alfonso Peterssen for another 1.5%. * Optimize hash collision check compare for ~4% gain. * Add perf stats based on latest version.
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Thomas Wuerthinger
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GitHub
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2bfd8f90bc
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af66ac145f
@@ -30,28 +30,30 @@ import java.util.stream.IntStream;
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/**
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* Simple solution that memory maps the input file, then splits it into one segment per available core and uses
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* sun.misc.Unsafe to directly access the mapped memory.
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*
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* Runs in 0.92s on my Intel i9-13900K
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* sun.misc.Unsafe to directly access the mapped memory. Uses a long at a time when checking for collision.
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* <p>
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* Runs in 0.70s on my Intel i9-13900K
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* Perf stats:
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* 65,004,666,383 cpu_core/cycles/
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* 71,141,249,972 cpu_atom/cycles/
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* 40,622,862,783 cpu_core/cycles/
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* 48,241,929,925 cpu_atom/cycles/
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*/
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public class CalculateAverage_thomaswue {
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private static final String FILE = "./measurements.txt";
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// Holding the current result for a single city.
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private static class Result {
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short min;
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short max;
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final long nameAddress;
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long lastNameLong;
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int remainingShift;
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int min;
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int max;
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long sum;
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int count;
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final long nameAddress;
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private Result(long nameAddress, int value) {
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this.nameAddress = nameAddress;
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this.min = (short) value;
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this.max = (short) value;
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this.min = value;
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this.max = value;
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this.sum = value;
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this.count = 1;
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}
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@@ -66,8 +68,8 @@ public class CalculateAverage_thomaswue {
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// Accumulate another result into this one.
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private void add(Result other) {
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min = (short) Math.min(min, other.min);
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max = (short) Math.max(max, other.max);
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min = Math.min(min, other.min);
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max = Math.max(max, other.max);
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sum += other.sum;
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count += other.count;
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}
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@@ -81,8 +83,7 @@ public class CalculateAverage_thomaswue {
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// Parallel processing of segments.
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List<HashMap<String, Result>> allResults = IntStream.range(0, chunks.length - 1).mapToObj(chunkIndex -> {
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HashMap<String, Result> cities = HashMap.newHashMap(1 << 10);
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Result[] results = new Result[1 << 18];
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parseLoop(chunks[chunkIndex], chunks[chunkIndex + 1], results, cities);
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parseLoop(chunks[chunkIndex], chunks[chunkIndex + 1], cities);
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return cities;
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}).parallel().toList();
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@@ -114,69 +115,60 @@ public class CalculateAverage_thomaswue {
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}
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}
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private static void parseLoop(long chunkStart, long chunkEnd, Result[] results, HashMap<String, Result> cities) {
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private static void parseLoop(long chunkStart, long chunkEnd, HashMap<String, Result> cities) {
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Result[] results = new Result[1 << 18];
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long scanPtr = chunkStart;
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byte b;
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while (scanPtr < chunkEnd) {
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long nameAddress = scanPtr;
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int hash = 0;
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long hash = 0;
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// Skip first letter.
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scanPtr++;
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// Scan for ';' delimiter, always 4 bytes at a time.
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while (true) {
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int nextVal = UNSAFE.getInt(scanPtr);
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if ((nextVal & 0x3B) == 0x3B) {
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scanPtr++;
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break;
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// Search for ';', one long at a time.
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long word = UNSAFE.getLong(scanPtr);
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int pos = findDelimiter(word);
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if (pos != 8) {
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scanPtr += pos;
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word = word & (-1L >>> ((8 - pos - 1) << 3));
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hash ^= word;
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}
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else {
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scanPtr += 8;
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hash ^= word;
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while (true) {
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word = UNSAFE.getLong(scanPtr);
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pos = findDelimiter(word);
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if (pos != 8) {
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scanPtr += pos;
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word = word & (-1L >>> ((8 - pos - 1) << 3));
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hash ^= word;
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break;
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}
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else {
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scanPtr += 8;
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hash ^= word;
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}
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}
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else if ((nextVal & 0x3B00) == 0x3B00) {
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scanPtr += 2;
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hash = hash ^ (nextVal & 0xFF);
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break;
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}
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else if ((nextVal & 0x3B0000) == 0x3B0000) {
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scanPtr += 3;
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hash = hash ^ (nextVal & 0xFFFF);
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break;
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}
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else if (((nextVal & 0x3B000000) == 0x3B000000)) {
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scanPtr += 4;
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hash = hash ^ (nextVal & 0xFFFFFF);
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break;
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}
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scanPtr += 4;
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hash = hash ^ nextVal;
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}
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// Save length of name for later.
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int nameLength = (int) (scanPtr - nameAddress - 1);
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int nameLength = (int) (scanPtr - nameAddress);
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scanPtr++;
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// Parse number.
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int number;
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byte sign = UNSAFE.getByte(scanPtr++);
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if (sign == '-') {
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number = UNSAFE.getByte(scanPtr++) - '0';
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if ((b = UNSAFE.getByte(scanPtr++)) != '.') {
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number = number * 10 + (b - '0');
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scanPtr++;
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}
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number = number * 10 + (UNSAFE.getByte(scanPtr++) - '0');
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number = -number;
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}
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else {
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number = sign - '0';
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if ((b = UNSAFE.getByte(scanPtr++)) != '.') {
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number = number * 10 + (b - '0');
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scanPtr++;
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}
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number = number * 10 + (UNSAFE.getByte(scanPtr++) - '0');
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}
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long numberWord = UNSAFE.getLong(scanPtr);
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// The 4th binary digit of the ascii of a digit is 1 while
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// that of the '.' is 0. This finds the decimal separator
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// The value can be 12, 20, 28
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int decimalSepPos = Long.numberOfTrailingZeros(~numberWord & 0x10101000);
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int number = convertIntoNumber(decimalSepPos, numberWord);
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// Skip past new line.
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// scanPtr++;
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scanPtr += (decimalSepPos >>> 3) + 3;
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// Final calculation for index into hash table.
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int tableIndex = (((hash ^ (hash >>> 18)) & (results.length - 1)));
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while (true) {
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int hashAsInt = (int) (hash ^ (hash >>> 32));
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int finalHash = (hashAsInt ^ (hashAsInt >>> 18));
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int tableIndex = (finalHash & (results.length - 1));
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outer: while (true) {
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Result existingResult = results[tableIndex];
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if (existingResult == null) {
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newEntry(results, cities, nameAddress, number, tableIndex, nameLength);
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@@ -184,35 +176,16 @@ public class CalculateAverage_thomaswue {
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}
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else {
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// Check for collision.
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boolean result = true;
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int i = 0;
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if ((long) nameLength >= 8) {
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if (UNSAFE.getLong(existingResult.nameAddress) != UNSAFE.getLong(nameAddress)) {
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result = false;
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}
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else {
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i += 8;
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for (; i < nameLength + 1 - 8; i += 8) {
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if (UNSAFE.getLong(existingResult.nameAddress + i) != UNSAFE.getLong(nameAddress + i)) {
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tableIndex = (tableIndex + 1) & (results.length - 1);
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continue outer;
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}
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}
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else if ((long) nameLength >= 4) {
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if (UNSAFE.getInt(existingResult.nameAddress) != UNSAFE.getInt(nameAddress)) {
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result = false;
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}
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else {
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i += 4;
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}
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}
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if (result) {
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for (; i < (long) nameLength; ++i) {
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if (UNSAFE.getByte(existingResult.nameAddress + i) != UNSAFE.getByte(nameAddress + i)) {
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result = false;
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break;
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}
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}
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}
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if (result) {
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existingResult.min = (short) Math.min(existingResult.min, number);
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existingResult.max = (short) Math.max(existingResult.max, number);
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if (((existingResult.lastNameLong ^ UNSAFE.getLong(nameAddress + i)) << existingResult.remainingShift) == 0) {
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existingResult.min = Math.min(existingResult.min, number);
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existingResult.max = Math.max(existingResult.max, number);
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existingResult.sum += number;
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existingResult.count++;
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break;
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@@ -223,18 +196,52 @@ public class CalculateAverage_thomaswue {
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}
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}
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}
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// Skip new line.
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scanPtr++;
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}
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}
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// Special method to convert a number in the specific format into an int value without branches created by
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// Quan Anh Mai.
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private static int convertIntoNumber(int decimalSepPos, long numberWord) {
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int shift = 28 - decimalSepPos;
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// signed is -1 if negative, 0 otherwise
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long signed = (~numberWord << 59) >> 63;
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long designMask = ~(signed & 0xFF);
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// Align the number to a specific position and transform the ascii code
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// to actual digit value in each byte
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long digits = ((numberWord & designMask) << shift) & 0x0F000F0F00L;
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// Now digits is in the form 0xUU00TTHH00 (UU: units digit, TT: tens digit, HH: hundreds digit)
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// 0xUU00TTHH00 * (100 * 0x1000000 + 10 * 0x10000 + 1) =
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// 0x000000UU00TTHH00 +
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// 0x00UU00TTHH000000 * 10 +
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// 0xUU00TTHH00000000 * 100
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// Now TT * 100 has 2 trailing zeroes and HH * 100 + TT * 10 + UU < 0x400
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// This results in our value lies in the bit 32 to 41 of this product
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// That was close :)
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long absValue = ((digits * 0x640a0001) >>> 32) & 0x3FF;
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long value = (absValue ^ signed) - signed;
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return (int) value;
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}
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private static int findDelimiter(long word) {
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long input = word ^ 0x3B3B3B3B3B3B3B3BL;
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long tmp = (input - 0x0101010101010101L) & ~input & 0x8080808080808080L;
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return Long.numberOfTrailingZeros(tmp) >>> 3;
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}
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private static void newEntry(Result[] results, HashMap<String, Result> cities, long nameAddress, int number, int hash, int nameLength) {
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Result r = new Result(nameAddress, number);
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results[hash] = r;
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byte[] bytes = new byte[nameLength];
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int i = 0;
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for (; i < nameLength + 1 - 8; i += 8) {
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}
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r.lastNameLong = UNSAFE.getLong(nameAddress + i);
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r.remainingShift = (64 - (nameLength + 1 - i) << 3);
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UNSAFE.copyMemory(null, nameAddress, bytes, Unsafe.ARRAY_BYTE_BASE_OFFSET, nameLength);
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cities.put(new String(bytes, StandardCharsets.UTF_8), r);
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String nameAsString = new String(bytes, StandardCharsets.UTF_8);
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cities.put(nameAsString, r);
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}
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private static long[] getSegments(int numberOfChunks) throws IOException {
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