an array of at least input_length*3/4 bytes
some base64 input
length of input in bytes
is an output parameter which says how many bytes of input were actually consumed. If less than input_length, then the range input[consumed:length] should be passed in later along with more input.
true iff this is the last input, in which case padding is allowed
ignore whitespace on input; if false, throw new an exception if whitespace is encountered
number of bytes written to output
Perform base64 decoding