convert method
Converts input
and returns the result of the conversion.
Implementation
@override
Uint8List convert(String input) {
int len = input.length;
if (len == 0) {
return Uint8List(0);
}
// Count '\r', '\n' and illegal characters, For illegal characters,
// throw an exception.
int extrasLen = 0;
for (int i = 0; i < len; i++) {
int c = _decodeTable[input.codeUnitAt(i)];
if (c < 0) {
extrasLen++;
if (c == -2) {
throw new FormatException('Invalid character: ${input[i]}');
}
}
}
if ((len - extrasLen) % 4 != 0) {
throw new FormatException('''Size of Base 64 characters in Input
must be a multiple of 4. Input: $input''');
}
// Count pad characters.
int padLength = 0;
for (int i = len - 1; i >= 0; i--) {
int currentCodeUnit = input.codeUnitAt(i);
if (_decodeTable[currentCodeUnit] > 0) break;
if (currentCodeUnit == _PAD) padLength++;
}
int outputLen = (((len - extrasLen) * 6) >> 3) - padLength;
var out = new Uint8List(outputLen);
for (int i = 0, o = 0; o < outputLen;) {
// Accumulate 4 valid 6 bit Base 64 characters into an int.
int x = 0;
for (int j = 4; j > 0;) {
int c = _decodeTable[input.codeUnitAt(i++)];
if (c >= 0) {
x = ((x << 6) & 0xFFFFFF) | c;
j--;
}
}
out[o++] = x >> 16;
if (o < outputLen) {
out[o++] = (x >> 8) & 0xFF;
if (o < outputLen) out[o++] = x & 0xFF;
}
}
return out;
}