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);
    }
}