Dandandan commented on a change in pull request #9116:
URL: https://github.com/apache/arrow/pull/9116#discussion_r554613147
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File path: rust/datafusion/src/physical_plan/hash_join.rs
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@@ -575,6 +542,199 @@ fn build_join_indexes(
}
}
}
+use core::hash::BuildHasher;
+
+/// `Hasher` that returns the same `u64` value as a hash, to avoid re-hashing
+/// it when inserting/indexing or regrowing the `HashMap`
+struct IdHasher {
+ hash: u64,
+}
+
+impl Hasher for IdHasher {
+ fn finish(&self) -> u64 {
+ self.hash
+ }
+
+ fn write_u64(&mut self, i: u64) {
+ self.hash = i;
+ }
+
+ fn write(&mut self, _bytes: &[u8]) {
+ unreachable!("IdHasher should only be used for u64 keys")
+ }
+}
+
+#[derive(Debug)]
+struct IdHashBuilder {}
+
+impl BuildHasher for IdHashBuilder {
+ type Hasher = IdHasher;
+
+ fn build_hasher(&self) -> Self::Hasher {
+ IdHasher { hash: 0 }
+ }
+}
+
+// Combines two hashes into one hash
+fn combine_hashes(l: u64, r: u64) -> u64 {
Review comment:
Just a simple hashing combination function. Source:
http://myeyesareblind.com/2017/02/06/Combine-hash-values/
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