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perf(std): 4x unroll Hash.hashMem64 main loop #13

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perf(std): 4x unroll Hash.hashMem64 main loop #13

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12 changes: 12 additions & 0 deletions core/src/main/java/io/questdb/std/Hash.java
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Original file line number Diff line number Diff line change
Expand Up @@ -107,6 +107,18 @@ public static long hashLong64(long k) {
public static long hashMem64(long p, long len) {
long h = 0;
long i = 0;
// Unroll main loop by factor of 4 for better ILP
for (; i + 31 < len; i += 32) {
long v1 = Unsafe.getUnsafe().getLong(p + i);
long v2 = Unsafe.getUnsafe().getLong(p + i + 8);
long v3 = Unsafe.getUnsafe().getLong(p + i + 16);
long v4 = Unsafe.getUnsafe().getLong(p + i + 24);
h = h * M2 + v1;
h = h * M2 + v2;
h = h * M2 + v3;
h = h * M2 + v4;
}
// Handle remaining 8-byte chunks
for (; i + 7 < len; i += 8) {
h = h * M2 + Unsafe.getUnsafe().getLong(p + i);
}
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