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Entry for abhinav-upadhyay #696

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Entry for abhinav-upadhyay #696

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a110004
Add entry for GH user abhinav-upadhyay.
abhinav-upadhyay Jan 31, 2024
3a1d351
Fix output
abhinav-upadhyay Jan 31, 2024
baca219
Remove extra calls to min and max
abhinav-upadhyay Jan 31, 2024
10c68a1
Rename the script
abhinav-upadhyay Jan 31, 2024
833ff01
Hanle hash collisions
abhinav-upadhyay Jan 31, 2024
3429050
Fix the handling of hash collisions
abhinav-upadhyay Feb 1, 2024
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19 changes: 16 additions & 3 deletions src/main/java/dev/morling/onebrc/CalculateAverage_abhinavupadhyay.java
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Original file line number Diff line number Diff line change
Expand Up @@ -60,7 +60,6 @@ private static class Table {

public void put(long cityStartOffset, long cityLength, long nameHash, int temperature) {
final long uhash = nameHash ^ (nameHash >> 29);
// final long uhash = nameHash;
int index = (int) uhash & TABLE_MASK;
Row row = table[index];
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You'll need to handle collisions, otherwise you'd aggregate the values from several stations with the same hash.

if (row == null) {
Expand All @@ -72,7 +71,21 @@ public void put(long cityStartOffset, long cityLength, long nameHash, int temper
for (; i < cityLength; i++) {
array[i] = UNSAFE.getByte(cityStartOffset++);
}
table[index] = new Row(new String(array, 0, i), temperature, temperature, 1, temperature, (int) uhash);
table[index] = new Row(new String(array, 0, i), temperature, temperature, 1, temperature, uhash);
return;
}

while (row.hash != uhash) {
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Just checking the hash isn't enough, you'll need to compare the actual name to differentiate between multiple stations with the same hash.

index = (int) ((index + (uhash)) & TABLE_MASK);
int i = 0;
for (; i < cityLength - 1;) {
array[i++] = UNSAFE.getByte(cityStartOffset++);
array[i++] = UNSAFE.getByte(cityStartOffset++);
}
for (; i < cityLength; i++) {
array[i] = UNSAFE.getByte(cityStartOffset++);
}
table[index] = new Row(new String(array, 0, i), temperature, temperature, 1, temperature, uhash);
return;
}

Expand Down Expand Up @@ -214,7 +227,7 @@ public static void main(String[] args) throws IOException {
final long fileSize = fc.size();
final long startAddress = fc.map(FileChannel.MapMode.READ_ONLY, 0, fileSize, Arena.global()).address();
final long endAddress = startAddress + fileSize;
final long[][] segments = findSegments(startAddress, endAddress, fileSize, fileSize > 1024 * 1024 * 1024 ? 8 : 1);
final long[][] segments = findSegments(startAddress, endAddress, fileSize, fileSize > 1024 * 1024 * 1024 ? 12 : 1);
final List<Table> collect = Arrays.stream(segments).parallel().map(s -> readFile(s[0], s[1])).toList();
Map<String, Row> finalMap = new TreeMap<>();
for (final Table t : collect) {
Expand Down
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