private BitLock CreateAndIndexBitLock(IEnumerable <ushort> bitPositions)
{
var bitLock = new BitLock(bitPositions);
foreach (var bitPosition in bitPositions)
{
if (!this._locksByBits.TryGetValue(bitPosition, out var indexedLocks))
{
indexedLocks = new HashSet <BitLock>(ReferenceEqualityComparer <BitLock> .Default);
this._locksByBits.Add(bitPosition, indexedLocks);
}
indexedLocks.Add(bitLock);
}
return(bitLock);
}
private void DeindexBitLock(BitLock bitLock)
{
if (bitLock == null)
{
return;
}
foreach (var bitPosition in bitLock.BitPositions.Distinct())
{
var bitLocks = this._locksByBits[bitPosition];
bitLocks.Remove(bitLock);
if (!bitLocks.Any())
{
this._locksByBits.Remove(bitPosition);
}
}
}
public bool Unlocks(BitLock bitLock)
{
var totalKeySegments = this.Bits.Count;
var totalLockSegments = bitLock.Bits.Count;
if (totalLockSegments > totalKeySegments)
{
// If the lock is larger than the key, look first at all lock bytes past the key's length
var farLock = bitLock.Bits.Skip(totalKeySegments);
if (farLock.Any(x => x > 0))
{
// If any lock byte past the key's length has any bits flipped to 1, this key cannot possibly fit
return(false);
}
}
// Only look at the bytes of the key that have corresponding lock bytes
// i.e. if the key is longer than the lock, trim down the key to fit the lock
for (var segmentPos = 0; segmentPos < totalLockSegments; segmentPos++)
{
// Example:
// Key: 10010100
// Lock: 10110011
// O XO XX - passes 2 bits, fails 3 bits. Does NOT unlock.
// Key: 10010100
// Lock: 10000100
// O O - passes 2 bits. Unlock successful. Don't care about extra key bits.
var lockSegment = bitLock.Bits[segmentPos];
var keySegment = this.Bits[segmentPos];
if ((keySegment & lockSegment) != lockSegment)
{
return(false);
}
}
// If no bytes failed, then the unlock is successful
return(true);
}
