/**
* Calculates the checksum for the given data.
*
* @param charset the charset used in encoding the data
* @param data the data to calculate the checksum on
* @param isEntireMessage specifies whether the data is an entire message; if true, and it ends
* with a checksum field, that checksum field is excluded from the current checksum
* calculation
* @return the calculated checksum
*/
public static int checksum(Charset charset, String data, boolean isEntireMessage) {
int sum = 0;
if (CharsetSupport.isStringEquivalent(charset)) { // optimization - skip encoding
int end = isEntireMessage ? data.lastIndexOf("\00110=") : -1;
int len = end > -1 ? end + 1 : data.length();
for (int i = 0; i < len; i++) {
sum += data.charAt(i);
}
} else {
byte[] bytes = data.getBytes(charset);
int len = bytes.length;
if (isEntireMessage
&& bytes[len - 8] == '\001'
&& bytes[len - 7] == '1'
&& bytes[len - 6] == '0'
&& bytes[len - 5] == '=') len = len - 7;
for (int i = 0; i < len; i++) {
sum += (bytes[i] & 0xFF);
}
}
return sum & 0xFF; // better than sum % 256 since it avoids overflow issues
}
/**
* Calculates the length of the byte representation of the given string in the given charset.
*
* @param charset the charset used in encoding the data
* @param data the data to calculate the length on
* @return the calculated length
*/
public static int length(Charset charset, String data) {
return CharsetSupport.isStringEquivalent(charset)
? data.length()
: data.getBytes(charset).length;
}