internal LookupTable GetOrCreateLookupTable(string alphabet)
{
return(_lookupTable ?? (_lookupTable = BuildLookupTable(alphabet)));
}
private static unsafe bool CheckAlphabet(string encoded, int index, int length, LookupTable lookupTable)
{
int[] lookupValues = lookupTable.Values;
int lowCode = lookupTable.LowCode;
int lookupSize = lookupValues.Length;
fixed(char *pEncodedBegin = encoded)
fixed(int *pLookup = lookupValues)
{
char *pEncoded = pEncodedBegin + index;
char *pEnd = pEncoded + length;
while (pEncoded < pEnd)
{
int lookupIndex = *pEncoded - lowCode;
if (lookupIndex < 0 || lookupIndex >= lookupSize)
{
return(false);
}
int item = *(pLookup + lookupIndex);
if (item == LookupTableNullItem)
{
return(false);
}
pEncoded++;
}
}
return(true);
}
internal static byte[] ToBytes(string encoded, int index, int length, char?padSymbol, LookupTable lookupTable)
{
CheckToBytesArguments(encoded, index, length, lookupTable);
if (length == 0)
{
return(new byte[0]);
}
int remainder = GetRemainderWithChecks(encoded, index, length, padSymbol);
int groupsCount = length / 8;
int bytesCount = 0;
if (remainder > 0)
{
if (padSymbol != null)
{
// groupsCount always >= 1 here because of "length % 8 != 0" as checked before
groupsCount--;
}
bytesCount = GetBytesCount(remainder);
}
bytesCount += groupsCount * 5;
var bytes = new byte[bytesCount];
if (bytesCount > 0)
{
ToBytesUnsafe(encoded, index, bytes, 0, groupsCount, remainder, lookupTable);
}
return(bytes);
}
private static void CheckToBytesArguments(string encoded, int index, int length, LookupTable lookupTable)
{
if (encoded == null)
{
throw new ArgumentNullException(nameof(encoded));
}
if (index < 0)
{
throw new ArgumentOutOfRangeException(nameof(index));
}
if (length < 0 || length > encoded.Length - index)
{
throw new ArgumentOutOfRangeException(nameof(length));
}
if (lookupTable == null)
{
throw new ArgumentNullException(nameof(lookupTable));
}
}
private static unsafe void ToBytesUnsafe(string encoded, int index, byte[] output, int outputOffset,
int encodedGroupsCount, int remainder, LookupTable lookupTable)
{
int[] lookupValues = lookupTable.Values;
int lowCode = lookupTable.LowCode;
fixed(char *pEncodedBegin = encoded)
fixed(byte *pOutput = &output[outputOffset])
fixed(int *pLookup = lookupValues)
{
char *pEncoded = pEncodedBegin + index;
if (encodedGroupsCount > 0)
{
ToBytesGroupsUnsafe(pEncoded, pOutput, encodedGroupsCount, pLookup,
lookupValues.Length, lowCode);
}
if (remainder <= 1)
{
return;
}
char *pEncodedRemainder = pEncoded + encodedGroupsCount * 8;
byte *pOutputRemainder = pOutput + encodedGroupsCount * 5;
ToBytesRemainderUnsafe(pEncodedRemainder, pOutputRemainder, remainder, pLookup,
lookupValues.Length, lowCode);
}
}
internal static byte[] ToBytes(string encoded, int index, int length, char?padSymbol, LookupTable lookupTable)
{
if (encoded == null)
{
throw new ArgumentNullException(nameof(encoded));
}
if (index < 0)
{
throw new ArgumentOutOfRangeException(nameof(index));
}
if (length < 0 || length > encoded.Length - index)
{
throw new ArgumentOutOfRangeException(nameof(length));
}
if (lookupTable == null)
{
throw new ArgumentNullException(nameof(lookupTable));
}
if (length == 0)
{
return(new byte[0]);
}
int remainder;
if (padSymbol != null)
{
if (length % 8 != 0)
{
throw new FormatException(ErrorMessageInvalidLength);
}
remainder = 8;
char padChar = padSymbol.Value;
for (int i = index + length - 1; i >= index; i--)
{
if (encoded[i] != padChar)
{
break;
}
remainder--;
}
if (remainder <= 0)
{
throw new FormatException(ErrorMessageInvalidPadding);
}
remainder %= 8;
}
else
{
remainder = length % 8;
}
int groupsCount = length / 8;
int bytesCount = 0;
if (remainder > 0)
{
if (padSymbol != null)
{
// groupsCount was checked before and always >= 1 here
groupsCount--;
}
bytesCount = GetBytesCount(remainder);
}
bytesCount += groupsCount * 5;
var bytes = new byte[bytesCount];
if (bytesCount > 0)
{
ToBytesUnsafe(encoded, index, length, bytes, 0, groupsCount, remainder, padSymbol, lookupTable);
}
return(bytes);
}
