From 48f7e22d9cc93989173afe2550fcc2f082c61773 Mon Sep 17 00:00:00 2001
From: Steven Le Rouzic <steven.lerouzic@gmail.com>
Date: Mon, 6 Jan 2025 00:33:50 +0100
Subject: Start work on hashing

---
 asl/hash.hpp             | 45 +++++++++++++++++++++++++++++++++++++++++++--
 asl/meta.hpp             |  7 +++++++
 asl/tests/meta_tests.cpp |  4 ++++
 3 files changed, 54 insertions(+), 2 deletions(-)

(limited to 'asl')

diff --git a/asl/hash.hpp b/asl/hash.hpp
index 6190e8f..5eb64f6 100644
--- a/asl/hash.hpp
+++ b/asl/hash.hpp
@@ -1,12 +1,12 @@
 #pragma once
 
 #include "asl/integers.hpp"
+#include "asl/meta.hpp"
+#include "asl/utility.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);
 
@@ -51,3 +51,44 @@ constexpr uint64_t Hash128to64(const uint128_t& x)
 }
 
 } // namespace asl::city_hash
+
+namespace asl
+{
+
+template<typename T, typename H>
+concept hashable_generic = requires(const T& value, H h)
+{
+    { AslHashValue(h, value) } -> same_as<H>;
+};
+
+struct HashState
+{
+    uint128_t state{};
+
+    constexpr HashState() = default;
+    explicit constexpr HashState(uint128_t s) : state{s} {}
+
+    static constexpr HashState combine(HashState h)
+    {
+        return h;
+    }
+
+    template<hashable_generic<HashState> Arg, hashable_generic<HashState>... Remaining>
+    static constexpr HashState combine(HashState h, const Arg& arg, const Remaining&... remaining)
+    {
+        return combine(AslHashValue(h, arg), remaining...);
+    }
+};
+
+template<typename T>
+concept hashable = hashable_generic<T, HashState>;
+
+template<typename H, uniquely_represented T>
+constexpr H AslHashValue(H h, const T& value)
+{
+    auto hashed = city_hash::CityHash128WithSeed(reinterpret_cast<const char*>(&value), size_of<T>, h.state);
+    return HashState{hashed};
+}
+
+} // namespace asl
+
diff --git a/asl/meta.hpp b/asl/meta.hpp
index 84616f4..c353b0f 100644
--- a/asl/meta.hpp
+++ b/asl/meta.hpp
@@ -189,6 +189,13 @@ template<>           struct _is_integer_helper<uint64_t> : true_type  {};
 
 template<typename T> concept is_integer = _is_integer_helper<un_cv_t<T>>::value;
 
+template<typename T> struct is_uniquely_represented : false_type {};
+template<is_integer T> struct is_uniquely_represented<T> : true_type {};
+template<> struct is_uniquely_represented<uint128_t> : true_type {};
+template<> struct is_uniquely_represented<byte> : true_type {};
+
+template<typename T> concept uniquely_represented = is_uniquely_represented<T>::value;
+
 template<typename T, typename U>
 concept equality_comparable_with = requires (const un_cvref_t<T>& a, const un_cvref_t<U>& b)
 {
diff --git a/asl/tests/meta_tests.cpp b/asl/tests/meta_tests.cpp
index 24e9754..4fedd71 100644
--- a/asl/tests/meta_tests.cpp
+++ b/asl/tests/meta_tests.cpp
@@ -232,3 +232,7 @@ static_assert(asl::is_floating_point<volatile double>);
 static_assert(!asl::is_floating_point<const float&>);
 static_assert(!asl::is_floating_point<int>);
 static_assert(!asl::is_floating_point<C>);
+
+static_assert(asl::uniquely_represented<int>);
+static_assert(asl::uniquely_represented<uint128_t>);
+static_assert(!asl::uniquely_represented<bool>);
-- 
cgit