Rename because it is ordered

PersistentOrderedMap/KeyStrategies/DoubleStrategy.cs

@@ -0,0 +1,34 @@
+namespace PersistentOrderedMap;
+using System.Runtime.CompilerServices;
+
+public struct DoubleStrategy : IKeyStrategy<double>
+{
+    public bool IsLossless => true;
+    // Use the standard comparison for the fallback/refine step
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public int Compare(double x, double y) => x.CompareTo(y);
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public long GetPrefix(double key)
+    {
+        // 1. Bit Cast to Long (0 cost)
+        long bits = Unsafe.As<double, long>(ref key);
+
+        // 2. The Magic Twist
+        // If the sign bit (MSB) is set (negative), we flip ALL bits.
+        // If the sign bit is clear (positive), we flip ONLY the sign bit.
+        // This maps:
+        //  -Negative Max -> 0
+        //  -0            -> Midpoint
+        //  +Negative Max -> Max
+
+        long mask = (bits >> 63); // 0 for positive, -1 (All 1s) for negative
+
+        // If negative: bits ^ -1 = ~bits (Flip All)
+        // If positive: bits ^ 0  = bits (Flip None)
+        // Then we toggle the sign bit (0x8000...) to shift the range to signed long.
+
+        return (bits ^ (mask & 0x7FFFFFFFFFFFFFFF)) ^ unchecked((long)0x8000000000000000);
+    }
+}
+