1 files changed, 104 insertions, 0 deletions
diff --git a/src/include/common/hashfn.h b/src/include/common/hashfn.h
new file mode 100644
index 0000000..c634cc0
--- /dev/null
+++ b/src/include/common/hashfn.h
@@ -0,0 +1,104 @@
+/*
+ * Utilities for working with hash values.
+ *
+ * Portions Copyright (c) 2017-2021, PostgreSQL Global Development Group
+ */
+
+#ifndef HASHFN_H
+#define HASHFN_H
+
+
+/*
+ * Rotate the high 32 bits and the low 32 bits separately.  The standard
+ * hash function sometimes rotates the low 32 bits by one bit when
+ * combining elements.  We want extended hash functions to be compatible with
+ * that algorithm when the seed is 0, so we can't just do a normal rotation.
+ * This works, though.
+ */
+#define ROTATE_HIGH_AND_LOW_32BITS(v) \
+	((((v) << 1) & UINT64CONST(0xfffffffefffffffe)) | \
+	(((v) >> 31) & UINT64CONST(0x100000001)))
+
+
+extern uint32 hash_bytes(const unsigned char *k, int keylen);
+extern uint64 hash_bytes_extended(const unsigned char *k,
+								  int keylen, uint64 seed);
+extern uint32 hash_bytes_uint32(uint32 k);
+extern uint64 hash_bytes_uint32_extended(uint32 k, uint64 seed);
+
+#ifndef FRONTEND
+static inline Datum
+hash_any(const unsigned char *k, int keylen)
+{
+	return UInt32GetDatum(hash_bytes(k, keylen));
+}
+
+static inline Datum
+hash_any_extended(const unsigned char *k, int keylen, uint64 seed)
+{
+	return UInt64GetDatum(hash_bytes_extended(k, keylen, seed));
+}
+
+static inline Datum
+hash_uint32(uint32 k)
+{
+	return UInt32GetDatum(hash_bytes_uint32(k));
+}
+
+static inline Datum
+hash_uint32_extended(uint32 k, uint64 seed)
+{
+	return UInt64GetDatum(hash_bytes_uint32_extended(k, seed));
+}
+#endif
+
+extern uint32 string_hash(const void *key, Size keysize);
+extern uint32 tag_hash(const void *key, Size keysize);
+extern uint32 uint32_hash(const void *key, Size keysize);
+
+#define oid_hash uint32_hash	/* Remove me eventually */
+
+/*
+ * Combine two 32-bit hash values, resulting in another hash value, with
+ * decent bit mixing.
+ *
+ * Similar to boost's hash_combine().
+ */
+static inline uint32
+hash_combine(uint32 a, uint32 b)
+{
+	a ^= b + 0x9e3779b9 + (a << 6) + (a >> 2);
+	return a;
+}
+
+/*
+ * Combine two 64-bit hash values, resulting in another hash value, using the
+ * same kind of technique as hash_combine().  Testing shows that this also
+ * produces good bit mixing.
+ */
+static inline uint64
+hash_combine64(uint64 a, uint64 b)
+{
+	/* 0x49a0f4dd15e5a8e3 is 64bit random data */
+	a ^= b + UINT64CONST(0x49a0f4dd15e5a8e3) + (a << 54) + (a >> 7);
+	return a;
+}
+
+/*
+ * Simple inline murmur hash implementation hashing a 32 bit integer, for
+ * performance.
+ */
+static inline uint32
+murmurhash32(uint32 data)
+{
+	uint32		h = data;
+
+	h ^= h >> 16;
+	h *= 0x85ebca6b;
+	h ^= h >> 13;
+	h *= 0xc2b2ae35;
+	h ^= h >> 16;
+	return h;
+}
+
+#endif							/* HASHFN_H */