From 9971cd1d55b0481a2af74a7694b6dcf686176c7c Mon Sep 17 00:00:00 2001
From: Morph <39850852+Morph1984@users.noreply.github.com>
Date: Sat, 25 Mar 2023 22:43:55 -0400
Subject: common: Port boost's hash_value implementation

Ports a small subset of boost's hash_value implementation (<= 1.80.0).
---
 src/common/container_hash.h | 91 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)
 create mode 100644 src/common/container_hash.h

(limited to 'src/common/container_hash.h')

diff --git a/src/common/container_hash.h b/src/common/container_hash.h
new file mode 100644
index 000000000..cfc5dfea8
--- /dev/null
+++ b/src/common/container_hash.h
@@ -0,0 +1,91 @@
+// SPDX-FileCopyrightText: 2005-2014 Daniel James
+// SPDX-FileCopyrightText: 2016 Austin Appleby
+// SPDX-License-Identifier: BSL-1.0
+
+#include <array>
+#include <cstdint>
+#include <limits>
+#include <type_traits>
+#include <vector>
+
+namespace Common {
+
+namespace detail {
+
+template <typename T>
+    requires std::is_unsigned_v<T>
+inline std::size_t HashValue(T val) {
+    const unsigned int size_t_bits = std::numeric_limits<std::size_t>::digits;
+    const unsigned int length =
+        (std::numeric_limits<T>::digits - 1) / static_cast<unsigned int>(size_t_bits);
+
+    std::size_t seed = 0;
+
+    for (unsigned int i = length * size_t_bits; i > 0; i -= size_t_bits) {
+        seed ^= static_cast<size_t>(val >> i) + (seed << 6) + (seed >> 2);
+    }
+
+    seed ^= static_cast<size_t>(val) + (seed << 6) + (seed >> 2);
+
+    return seed;
+}
+
+template <size_t Bits>
+struct HashCombineImpl {
+    template <typename T>
+    static inline T fn(T seed, T value) {
+        seed ^= value + 0x9e3779b9 + (seed << 6) + (seed >> 2);
+        return seed;
+    }
+};
+
+template <>
+struct HashCombineImpl<64> {
+    static inline std::uint64_t fn(std::uint64_t h, std::uint64_t k) {
+        const std::uint64_t m = (std::uint64_t(0xc6a4a793) << 32) + 0x5bd1e995;
+        const int r = 47;
+
+        k *= m;
+        k ^= k >> r;
+        k *= m;
+
+        h ^= k;
+        h *= m;
+
+        // Completely arbitrary number, to prevent 0's
+        // from hashing to 0.
+        h += 0xe6546b64;
+
+        return h;
+    }
+};
+
+} // namespace detail
+
+template <typename T>
+inline void HashCombine(std::size_t& seed, const T& v) {
+    seed = detail::HashCombineImpl<sizeof(std::size_t) * CHAR_BIT>::fn(seed, detail::HashValue(v));
+}
+
+template <typename It>
+inline std::size_t HashRange(It first, It last) {
+    std::size_t seed = 0;
+
+    for (; first != last; ++first) {
+        HashCombine<typename std::iterator_traits<It>::value_type>(seed, *first);
+    }
+
+    return seed;
+}
+
+template <typename T, size_t Size>
+std::size_t HashValue(const std::array<T, Size>& v) {
+    return HashRange(v.cbegin(), v.cend());
+}
+
+template <typename T, typename Allocator>
+std::size_t HashValue(const std::vector<T, Allocator>& v) {
+    return HashRange(v.cbegin(), v.cend());
+}
+
+} // namespace Common
-- 
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