using System;
using System.Runtime.InteropServices;
using static System.Buffers.Binary.BinaryPrimitives;
namespace PKHeX.Core;
///
/// Genius Sonority's logic for and encryption.
///
public static class GeniusCrypto
{
public static void ReadKeys(ReadOnlySpan input, Span keys)
{
for (int i = 0; i < keys.Length; i++)
keys[i] = ReadUInt16BigEndian(input[(i * 2)..]);
}
public static void Decrypt(ReadOnlySpan input, Span output, Span keys)
{
if (keys.Length != 4)
throw new ArgumentOutOfRangeException(nameof(keys));
var in16 = MemoryMarshal.Cast(input);
var out16 = MemoryMarshal.Cast(output);
int i = 0;
do
{
foreach (var key in keys)
{
var value = in16[i];
if (BitConverter.IsLittleEndian)
value = ReverseEndianness(value);
value -= key;
if (BitConverter.IsLittleEndian)
value = ReverseEndianness(value);
out16[i] = value;
i++;
}
AdvanceKeys(keys);
} while (i != in16.Length);
}
public static void Encrypt(ReadOnlySpan input, Span output, Span keys)
{
if (keys.Length != 4)
throw new ArgumentOutOfRangeException(nameof(keys));
var in16 = MemoryMarshal.Cast(input);
var out16 = MemoryMarshal.Cast(output);
int i = 0;
do
{
foreach (var key in keys)
{
var value = in16[i];
if (BitConverter.IsLittleEndian)
value = ReverseEndianness(value);
value += key;
if (BitConverter.IsLittleEndian)
value = ReverseEndianness(value);
out16[i] = value;
i++;
}
AdvanceKeys(keys);
} while (i != in16.Length);
}
private static void AdvanceKeys(Span keys)
{
var k3 = keys[3] + 0x13;
var k2 = keys[2] + 0x17;
var k1 = keys[1] + 0x29;
var k0 = keys[0] + 0x43;
// Rotate 4bit groups across the diagonal [ / ] after biasing each u16 (no overflow):
// 0123 FB73
// 4567 EA62
// 89AB becomes D951
// CDEF C840
// We can leave our intermediary types as int as the bit-masks remove any overflow.
keys[3] = (ushort)(((k0 >> 12) & 0xf) | ((k1 >> 8) & 0xf0) | ((k2 >> 4) & 0xf00) | ( k3 & 0xf000));
keys[2] = (ushort)(((k0 >> 08) & 0xf) | ((k1 >> 4) & 0xf0) | ( k2 & 0xf00) | ((k3 << 04) & 0xf000));
keys[1] = (ushort)(((k0 >> 04) & 0xf) | ( k1 & 0xf0) | ((k2 << 4) & 0xf00) | ((k3 << 08) & 0xf000));
keys[0] = (ushort)(( k0 & 0xf) | ((k1 << 4) & 0xf0) | ((k2 << 8) & 0xf00) | ((k3 << 12) & 0xf000));
}
}