80 lines
1.4 KiB
C#
80 lines
1.4 KiB
C#
namespace PerfectNumbers.Core;
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public static class PrimesGenerator
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{
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private static uint[]? _primes;
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private static ulong[]? _primesPow2;
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public static readonly uint[] SmallPrimes = BuildSmallPrimesInternal();
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public static readonly ulong[] SmallPrimesPow2 = BuildSmallPrimesPow2Internal();
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private static uint[] BuildSmallPrimesInternal()
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{
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if (_primes == null)
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{
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BuildSmallPrimes();
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}
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return _primes!;
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}
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private static ulong[] BuildSmallPrimesPow2Internal()
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{
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if (_primesPow2 == null)
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{
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BuildSmallPrimes();
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}
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return _primesPow2!;
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}
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private static void BuildSmallPrimes()
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{
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uint limit = PerfectNumberConstants.PrimesLimit;
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var primes = new uint[limit];
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primes[0] = 2;
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var primesPow2 = new ulong[limit];
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primesPow2[0] = 4;
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int j;
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uint i = 3, p, sqrt;
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bool isPrime;
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int primeIndex = 1;
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for (; i <= limit; i += 2)
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{
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isPrime = true;
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sqrt = (uint)Math.Sqrt(i);
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for (j = 0; j < primeIndex; j++)
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{
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p = primes[j];
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if (p > sqrt)
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{
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break;
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}
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if (i % p == 0UL)
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{
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isPrime = false;
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break;
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}
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}
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if (isPrime)
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{
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primes[primeIndex] = i;
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primesPow2[primeIndex] = checked((ulong)i * i);
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primeIndex++;
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}
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}
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Array.Resize(ref primes, primeIndex);
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Array.Resize(ref primesPow2, primeIndex);
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_primes = primes;
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_primesPow2 = primesPow2;
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return;
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}
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} |