The Annoyance Filter.pdf - Fourmilab

66 BIG5 DECODER ANNOYANCE-FILTER §73
73. Big5 decoder.
This decoder extracts logical characters from byte streams encoded in Big5 encoding. In Big5, bytes
in the range # 00– # 7F are single ASCII characters. Bytes with the # 80 bit set are the first byte of a two
byte character, the second byte of which may have any value.
〈 Class definitions 10 〉 +≡
class Big5 MBCSdecoder : public MBCSdecoder {
public:
virtual string name (void)
{
return "Big5";
}
virtual int getNextDecodedChar (void); /∗ Get next decoded byte ∗/
};
74. Decode the next logical character. We return −1 when the end of the encoded line is encountered.
〈 Class implementations 11 〉 +≡
int Big5 MBCSdecoder ::getNextDecodedChar (void)
{
int c1 = getNextEncodedByte ( );
}
if ((c1 ≥ 0) ∧ ((c1 & # 80) ≠ 0)) {
int c2 = getNextEncodedByte ( );
if (c2 ≡ −1) {
ostringstream os ;
os ≪ name ( ) ≪ "_MBCSdecoder:␣Premature␣end␣of␣line␣in␣two␣byte␣character.";
reportDecoderDiagnostic(os );
return −1;
}
return (c1 ≪ 8) | c2 ;
}
return c1 ;