1 files changed, 53 insertions, 0 deletions
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