Repo created

libs/base/rolling_hash.hpp

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+#pragma once
+
+#include "base/assert.hpp"
+#include "base/math.hpp"
+
+#ifdef DEBUG
+#include <queue>
+#endif
+
+template <typename T, typename HashT>
+class RabinKarpRollingHasher
+{
+public:
+  using value_type = T;
+  using hash_type = HashT;
+
+  explicit RabinKarpRollingHasher(HashT multiplier) : m_multiplier(multiplier) {}
+
+  template <typename Iter>
+  hash_type Init(Iter it, uint64_t windowSize)
+  {
+    ASSERT_GREATER(m_windowSize, 0, ());
+    m_windowSize = windowSize;
+    m_removeMultiplier = math::PowUint(m_multiplier, m_windowSize - 1);
+#ifdef DEBUG
+    while (!m_queue.empty())
+      m_queue.pop();
+#endif
+    m_hash = 0;
+    for (uint64_t i = 0; i < m_windowSize; ++it, ++i)
+    {
+      m_hash = m_hash * m_multiplier + *it;
+#ifdef DEBUG
+      m_queue.push(*it);
+#endif
+    }
+    return m_hash;
+  }
+
+  hash_type Scroll(T const remove, T const add)
+  {
+    ASSERT_NOT_EQUAL(m_removeMultiplier, 0, (m_multiplier, m_windowSize, remove, add));
+    ASSERT_NOT_EQUAL(m_windowSize, 0, (m_multiplier, remove, add));
+#ifdef DEBUG
+    ASSERT_EQUAL(m_queue.front(), remove, ());
+    m_queue.pop();
+    m_queue.push(add);
+#endif
+    m_hash -= m_removeMultiplier * remove;
+    m_hash = m_hash * m_multiplier + add;
+    return m_hash;
+  }
+
+private:
+  hash_type m_hash = 0;
+  hash_type m_multiplier = 1;
+  hash_type m_removeMultiplier = 1;
+  uint64_t m_windowSize = 1;
+
+#ifdef DEBUG
+  std::queue<value_type> m_queue;
+#endif
+};
+
+class RabinKarpRollingHasher32 : public RabinKarpRollingHasher<uint32_t, uint32_t>
+{
+public:
+  RabinKarpRollingHasher32() : RabinKarpRollingHasher(1103515245U) {}
+};
+
+class RabinKarpRollingHasher64 : public RabinKarpRollingHasher<uint64_t, uint64_t>
+{
+public:
+  RabinKarpRollingHasher64() : RabinKarpRollingHasher(6364136223846793005ULL) {}
+};
+
+using RollingHasher32 = RabinKarpRollingHasher32;
+using RollingHasher64 = RabinKarpRollingHasher64;