From 159f38d4e12bbcc48799431f4b69321a445be8ca Mon Sep 17 00:00:00 2001
From: Steven Le Rouzic <steven.lerouzic@gmail.com>
Date: Sun, 5 Jan 2025 22:12:56 +0100
Subject: Add CityHash
---
asl/hash.hpp | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 53 insertions(+)
create mode 100644 asl/hash.hpp
(limited to 'asl/hash.hpp')
diff --git a/asl/hash.hpp b/asl/hash.hpp
new file mode 100644
index 0000000..6190e8f
--- /dev/null
+++ b/asl/hash.hpp
@@ -0,0 +1,53 @@
+#pragma once
+
+#include "asl/integers.hpp"
+
+namespace asl::city_hash
+{
+
+// All CityHash stuff below this point
+
+// Hash function for a byte array.
+uint64_t CityHash64(const char *s, size_t len);
+
+// Hash function for a byte array. For convenience, a 64-bit seed is also
+// hashed into the result.
+uint64_t CityHash64WithSeed(const char *s, size_t len, uint64_t seed);
+
+// Hash function for a byte array. For convenience, two seeds are also
+// hashed into the result.
+uint64_t CityHash64WithSeeds(const char *s, size_t len,
+ uint64_t seed0, uint64_t seed1);
+
+// Hash function for a byte array.
+uint128_t CityHash128(const char *s, size_t len);
+
+// Hash function for a byte array. For convenience, a 128-bit seed is also
+// hashed into the result.
+uint128_t CityHash128WithSeed(const char *s, size_t len, uint128_t seed);
+
+// Hash function for a byte array. Most useful in 32-bit binaries.
+uint32_t CityHash32(const char *s, size_t len);
+
+// Hash 128 input bits down to 64 bits of output.
+// This is intended to be a reasonably good hash function.
+constexpr uint64_t Hash128to64(uint64_t high, uint64_t low)
+{
+ // Murmur-inspired hashing.
+ const uint64_t kMul = 0x9ddfea08eb382d69ULL;
+ uint64_t a = (low ^ high) * kMul;
+ a ^= (a >> 47);
+ uint64_t b = (high ^ a) * kMul;
+ b ^= (b >> 47);
+ b *= kMul;
+ return b;
+}
+
+// Hash 128 input bits down to 64 bits of output.
+// This is intended to be a reasonably good hash function.
+constexpr uint64_t Hash128to64(const uint128_t& x)
+{
+ return Hash128to64(x.high, x.low);
+}
+
+} // namespace asl::city_hash
--
cgit