Align bit transform comments with original implementation

EvenPerfectBitScanner/Candidates/Transforms/CandidateBitTransform.cs

@@ -0,0 +1,51 @@
+using System.Runtime.CompilerServices;
+using System.Threading;
+
+namespace EvenPerfectBitScanner.Candidates.Transforms;
+
+internal static class CandidateBitTransform
+{
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    internal static ulong Transform(ulong value, ref ulong remainder, ref bool limitReached)
+    {
+        ulong original = value;
+        if (value > (ulong.MaxValue >> 1))
+        {
+            Volatile.Write(ref limitReached, true);
+            return value;
+        }
+
+        ulong next = (value << 1) | 1UL;
+        remainder = (remainder << 1) + 1UL;
+        // Mod6 lookup loses to `%` in the benches; stick with subtraction + modulo for correctness and speed.
+        while (remainder >= 6UL)
+        {
+            remainder -= 6UL;
+        }
+
+        value = remainder switch
+        {
+            0UL => 1UL,
+            1UL => 0UL,
+            2UL => 5UL,
+            3UL => 4UL,
+            4UL => 3UL,
+            _ => 2UL,
+        }; // 'value' now holds diff
+
+        if (next > ulong.MaxValue - value)
+        {
+            Volatile.Write(ref limitReached, true);
+            return original;
+        }
+
+        remainder += value;
+        // `% 6` remains faster per Mod6ComparisonBenchmarks; keep this modulo fold and continue using subtraction.
+        while (remainder >= 6UL)
+        {
+            remainder -= 6UL;
+        }
+
+        return next + value;
+    }
+}