Merge pull request #20 from mlemanczyk/codex/modify-evenperfectbitscanner-to-iterate-primes

Use prime merge iteration for EvenPerfectBitScanner

EvenPerfectBitScanner/EvenPerfectBitScanner.csproj

@@ -12,4 +12,8 @@
       <_Parameter1>EvenPerfectBitScanner.Tests</_Parameter1>
     </AssemblyAttribute>
   </ItemGroup>
+  <ItemGroup>
+    <PackageReference Include="Open.Numeric" Version="3.0.1" />
+    <PackageReference Include="Open.Numeric.Primes" Version="4.0.4" />
+  </ItemGroup>
 </Project>

EvenPerfectBitScanner/Program.cs

@@ -1,6 +1,7 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Text;
+using Open.Numeric.Primes;
 using PerfectNumbers.Core;
 using PerfectNumbers.Core.Gpu;
 
@@ -30,7 +31,13 @@ internal static class Program
         private static MersenneNumberDivisorGpuTester? _divisorTester;
         private static ulong? _orderWarmupLimitOverride;
         private static unsafe delegate*<ulong, ref ulong, ulong> _transformP;
-	private static long _state;
+        private static readonly object PrimeMergeSync = new();
+        private static readonly TrialDivision.U64.Memoized PrimeGenerator = new();
+        private static IEnumerator<ulong>? _primeEnumerator;
+        private static bool _hasNextPrime;
+        private static ulong _nextPrime;
+        private static ulong _currentCandidate;
+        private static ulong _currentRemainder;
 	private static bool _limitReached;
 	private static string? _resultsDir;
 	private static string? _resultsPrefix;
@@ -569,7 +576,7 @@ internal static class Program
 		}
 
                 Console.WriteLine("Starting scan...");
-		_state = ((long)currentP << 3) | (long)remainder;
+                InitializePrimeMerge(currentP, remainder);
                 Task[] tasks = new Task[threadCount];
 
 		for (int i = 0; i < threadCount; i++)
@@ -736,39 +743,104 @@ internal static class Program
                 return $"even_perfect_bit_scan_inc-{inc}_thr-{threads}_blk-{block}_mers-{mers}_mersdev-{mersenneDevice}_ntt-{ntt}_red-{red}_primesdev-{primesDevice}_{order}_orderdev-{orderDevice}_{gcd}_{work}_gputh-{gpuPrimeThreads}_llslice-{llSlice}_scanb-{gpuScanBatch}_warm-{warmupLimit}.csv";
         }
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static void InitializePrimeMerge(ulong startCandidate, ulong startRemainder)
+        {
+                lock (PrimeMergeSync)
+                {
+                        _currentCandidate = startCandidate;
+                        _currentRemainder = startRemainder;
+                        InitializePrimeEnumerator(startCandidate);
+                }
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static void InitializePrimeEnumerator(ulong startValue)
+        {
+                (_primeEnumerator as IDisposable)?.Dispose();
+                ulong begin = startValue;
+                _primeEnumerator = PrimeGenerator.StartingAt(in begin).GetEnumerator();
+                _hasNextPrime = MoveToNextPrime();
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static bool MoveToNextPrime()
+        {
+                if (_primeEnumerator is null)
+                {
+                        return false;
+                }
+
+                if (_primeEnumerator.MoveNext())
+                {
+                        _nextPrime = _primeEnumerator.Current;
+                        return true;
+                }
+
+                Volatile.Write(ref _limitReached, true);
+                return false;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private static bool EnsurePrimeForCandidate(ulong candidate)
+        {
+                if (!_hasNextPrime)
+                {
+                        return false;
+                }
+
+                while (_hasNextPrime && _nextPrime < candidate)
+                {
+                        _hasNextPrime = MoveToNextPrime();
+                }
+
+                return _hasNextPrime;
+        }
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static unsafe int ReserveBlock(ulong[] buffer, int blockSize)
         {
                 Span<ulong> bufferSpan = new(buffer);
-		ulong p, remainder;
-		long state, newState, original;
-		int count;
-		while (true)
-		{
-			state = Volatile.Read(ref _state);
-			p = (ulong)state >> 3;
-			remainder = ((ulong)state) & 7UL;
+                int count = 0;
 
-			count = 0;
-			while (count < blockSize && !Volatile.Read(ref _limitReached))
+                lock (PrimeMergeSync)
                 {
-				bufferSpan[count++] = p;
-				p = _transformP(p, ref remainder);
-			}
-
-			if (count == 0)
+                        if (!_hasNextPrime && !MoveToNextPrime())
                         {
                                 return 0;
                         }
 
-			newState = ((long)p << 3) | (long)remainder;
-			original = Interlocked.CompareExchange(ref _state, newState, state);
-			if (original == state)
+                        while (count < blockSize && !Volatile.Read(ref _limitReached))
                         {
+                                ulong candidate = _currentCandidate;
+
+                                if (!EnsurePrimeForCandidate(candidate))
+                                {
+                                        break;
+                                }
+
+                                if (_hasNextPrime && _nextPrime == candidate)
+                                {
+                                        bufferSpan[count++] = candidate;
+                                        _hasNextPrime = MoveToNextPrime();
+                                        if (!_hasNextPrime)
+                                        {
+                                                _currentCandidate = _transformP(candidate, ref _currentRemainder);
+                                                break;
+                                        }
+                                }
+
+                                _currentCandidate = _transformP(candidate, ref _currentRemainder);
+
+                                if (Volatile.Read(ref _limitReached))
+                                {
+                                        break;
+                                }
+                        }
+                }
+
                 return count;
         }
-		}
-	}
 
 	[MethodImpl(MethodImplOptions.AggressiveInlining)]
 	private static void PrintResult(ulong currentP, bool searchedMersenne, bool detailedCheck, bool isPerfect)