The Annoyance Filter.pdf - Fourmilab

70 UCS-2 UNICODE DECODER ANNOYANCE-FILTER §81
81. UCS-2 Unicode decoder.
UCS-2 encoding of Unicode is simply a sequence of 16 bit quantities, which may be stored in either
little-endian or big-endian order; usually identified by a Unicode Byte Order Mark at the start of the
file. Here we do not attempt to auto-sense byte order; it must be set by the setBigEndian method before
the decoder is used.
〈 Class definitions 10 〉 +≡
class UCS 2 Unicode MBCSdecoder : public Unicode MBCSdecoder {
protected:
bool bigEndian ;
public:
UCS 2 Unicode MBCSdecoder(bool isBigEndian = true )
{
setBigEndian (isBigEndian );
}
void setBigEndian (bool isBigEndian = true )
{
bigEndian = isBigEndian ;
}
virtual string name (void)
{
return "UCS_2_Unicode";
}
virtual int getNextDecodedChar (void); /∗ Get next decoded byte ∗/
};
82. Decode the next logical character. We return −1 when the end of the encoded line is encountered.
〈 Class implementations 11 〉 +≡
int UCS 2 Unicode MBCSdecoder ::getNextDecodedChar (void)
{
int c1 = getNextEncodedByte ( );
int c2 = getNextEncodedByte ( );
if (c2 ≡ −1) {
ostringstream os ;
os ≪ name ( ) ≪ "_MBCSdecoder:␣Premature␣end␣of␣line␣in␣two␣byte␣character.";
reportDecoderDiagnostic(os );
return −1;
}
if (bigEndian ) {
c1 = (c1 ≪ 8) | c2 ;
}
else {
c1 |= (c2 ≪ 8);
}
return c1 ;
}