Move src/backend/utils/hash/hashfn.c to src/common

This also involves renaming src/include/utils/hashutils.h, which
becomes src/include/common/hashfn.h. Perhaps an argument can be
made for keeping the hashutils.h name, but it seemed more
consistent to make it match the name of the file, and also more
descriptive of what is actually going on here.

Patch by me, reviewed by Suraj Kharage and Mark Dilger. Off-list
advice on how not to break the Windows build from Davinder Singh
and Amit Kapila.

Discussion: http://postgr.es/m/CA+TgmoaRiG4TXND8QuM6JXFRkM_1wL2ZNhzaUKsuec9-4yrkgw@mail.gmail.com

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 00000000000..6ecc864f840
--- /dev/null
+++ b/src/include/common/hashfn.h
@@ -0,0 +1,104 @@
+/*
+ * Utilities for working with hash values.
+ *
+ * Portions Copyright (c) 2017-2020, 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 */