public unsafe Span <byte> Decode(string text)
{
Require.NotNull(text, nameof(text));
int textLen = text.Length;
if (textLen == 0)
{
return(new byte[0]);
}
char allZeroChar = alphabet.AllZeroShortcut;
char allSpaceChar = alphabet.AllSpaceShortcut;
bool checkZero = allZeroChar != Base85Alphabet.NoShortcut;
bool checkSpace = allSpaceChar != Base85Alphabet.NoShortcut;
bool usingShortcuts = checkZero || checkSpace;
// allocate a larger buffer if we're using shortcuts
int decodeBufferLen = getDecodeBufferLength(textLen, usingShortcuts);
byte[] decodeBuffer = new byte[decodeBufferLen];
byte[] table = alphabet.ReverseLookupTable;
fixed(char *inputPtr = text)
fixed(byte *decodeBufferPtr = decodeBuffer)
{
byte *pDecodeBuffer = decodeBufferPtr;
char *pInput = inputPtr;
char *pInputEnd = pInput + textLen;
int blockIndex = 0;
long value = 0;
while (pInput != pInputEnd)
{
char c = *pInput++;
if (isWhiteSpace(c))
{
continue;
}
// handle shortcut characters
if (checkZero && c == allZeroChar)
{
writeShortcut(ref pDecodeBuffer, blockIndex, allZeroChar, 0);
continue;
}
if (checkSpace && c == allSpaceChar)
{
writeShortcut(ref pDecodeBuffer, blockIndex, allSpaceChar, allSpace);
continue;
}
// handle regular blocks
int x = table[c] - 1; // map character to byte value
if (x < 0)
{
throw alphabet.InvalidCharacter(c);
}
value = value * baseLength + x;
blockIndex += 1;
if (blockIndex == stringBlockSize)
{
writeDecodedValue(ref pDecodeBuffer, value, byteBlockSize);
blockIndex = 0;
value = 0;
}
}
if (blockIndex > 0)
{
// handle padding by treating the rest of the characters
// as "u"s. so both big endianness and bit weirdness work out okay.
for (int i = 0; i < stringBlockSize - blockIndex; i++)
{
value = value * baseLength + (baseLength - 1);
}
writeDecodedValue(ref pDecodeBuffer, value, blockIndex - 1);
}
int actualOutputLength = (int)(pDecodeBuffer - decodeBufferPtr);
return(new Span <byte>(decodeBufferPtr, actualOutputLength));
}
}
