Euler 1-5

project_euler/sieve.h

@@ -0,0 +1,56 @@
+#ifndef SIEVE_H
+#define SIEVE_H
+
+#include <array>
+#include <concepts>
+#include <cstdint>
+
+template <std::uint64_t Max>
+class Sieve
+{
+    std::array<bool, Max> _primes{};
+
+    public:
+        Sieve()
+        {
+            for (bool& primeness : _primes)
+                primeness = true;
+
+            for (std::size_t idx = 3; idx < static_cast<std::size_t>(std::sqrt(Max)); idx += 2)
+            {
+                if (!_primes[index(idx)])
+                    continue;
+
+                for (std::size_t value = (2 * idx); value < Max; value += idx)
+                {
+                    if (value % 2 == 0)
+                        continue;
+                    _primes[index(value)] = false;
+                }
+            }
+        }
+
+        bool is_prime(std::uint64_t number) const noexcept
+        {
+            if (number == 2)
+                return true;
+            
+            if ((number == 0) || (number >= Max) || (number % 2 == 0))
+                return false;
+
+            return _primes[index(number)];
+        }
+
+        std::uint64_t size() const noexcept
+        {
+            return Max;
+        }
+
+    private:
+        std::size_t index(std::int64_t number) const noexcept
+        {
+            return (number - 1) / 2;
+        }
+};
+
+#endif