/// <summary>
/// Return the shuffled validator index corresponding to ``seed`` (and ``index_count``).
/// </summary>
public ValidatorIndex ComputeShuffledIndex(ValidatorIndex index, ulong indexCount, Hash32 seed)
{
if (index >= indexCount)
{
throw new ArgumentOutOfRangeException(nameof(index), index, $"Index should be less than indexCount {indexCount}");
}
// Swap or not (https://link.springer.com/content/pdf/10.1007%2F978-3-642-32009-5_1.pdf)
// See the 'generalized domain' algorithm on page 3
Span <byte> pivotHashInput = new Span <byte>(new byte[33]);
seed.AsSpan().CopyTo(pivotHashInput);
Span <byte> sourceHashInput = new Span <byte>(new byte[37]);
seed.AsSpan().CopyTo(sourceHashInput);
for (int currentRound = 0; currentRound < _miscellaneousParameterOptions.CurrentValue.ShuffleRoundCount; currentRound++)
{
byte roundByte = (byte)(currentRound & 0xFF);
pivotHashInput[32] = roundByte;
Hash32 pivotHash = _cryptographyService.Hash(pivotHashInput);
byte[] pivotBytes = pivotHash.AsSpan().Slice(0, 8).ToArray();
if (!BitConverter.IsLittleEndian)
{
pivotBytes = pivotBytes.Reverse().ToArray();
}
ValidatorIndex pivot = BitConverter.ToUInt64(pivotBytes.ToArray()) % indexCount;
ValidatorIndex flip = (pivot + indexCount - index) % indexCount;
ValidatorIndex position = ValidatorIndex.Max(index, flip);
sourceHashInput[32] = roundByte;
byte[] positionBytes = BitConverter.GetBytes((uint)position / 256);
if (!BitConverter.IsLittleEndian)
{
positionBytes = positionBytes.Reverse().ToArray();
}
positionBytes.CopyTo(sourceHashInput.Slice(33));
Hash32 source = _cryptographyService.Hash(sourceHashInput.ToArray());
byte flipByte = source.AsSpan((int)((uint)position % 256 / 8), 1)[0];
int flipBit = (flipByte >> (int)(position % 8)) % 2;
if (flipBit == 1)
{
index = flip;
}
}
return(index);
}
/// <summary>
/// Return the shuffled validator index corresponding to ``seed`` (and ``index_count``).
/// </summary>
public ValidatorIndex ComputeShuffledIndex(ValidatorIndex index, ulong indexCount, Bytes32 seed)
{
if (index >= indexCount)
{
throw new ArgumentOutOfRangeException(nameof(index), index,
$"Index should be less than indexCount {indexCount}");
}
// Swap or not (https://link.springer.com/content/pdf/10.1007%2F978-3-642-32009-5_1.pdf)
// See the 'generalized domain' algorithm on page 3
Span <byte> pivotHashInput = stackalloc byte[33];
seed.AsSpan().CopyTo(pivotHashInput);
Span <byte> sourceHashInput = stackalloc byte[37];
seed.AsSpan().CopyTo(sourceHashInput);
for (int currentRound = 0;
currentRound < _miscellaneousParameterOptions.CurrentValue.ShuffleRoundCount;
currentRound++)
{
byte roundByte = (byte)(currentRound & 0xFF);
pivotHashInput[32] = roundByte;
Bytes32 pivotHash = _cryptographyService.Hash(pivotHashInput);
ReadOnlySpan <byte> pivotBytes = pivotHash.AsSpan().Slice(0, 8);
ValidatorIndex pivot = BinaryPrimitives.ReadUInt64LittleEndian(pivotBytes) % indexCount;
ValidatorIndex flip = (pivot + indexCount - index) % indexCount;
ValidatorIndex position = ValidatorIndex.Max(index, flip);
sourceHashInput[32] = roundByte;
BinaryPrimitives.WriteUInt32LittleEndian(sourceHashInput.Slice(33), (uint)position / 256);
Bytes32 source = _cryptographyService.Hash(sourceHashInput.ToArray());
byte flipByte = source.AsSpan()[(int)((position % 256) / 8)];
int flipBit = (flipByte >> (int)(position % 8)) % 2;
if (flipBit == 1)
{
index = flip;
}
}
return(index);
}
