Dingtek DF555 decoder

A simple decoder works fine with Datacake.
hex payload 8000050211 032c 00 0f 0000000000220081
correctly returns
“DISTANCE”: 812,
“TEMPERATURE”: “15.00”

temperature is one byte, not sure how to return a minus degree

function Decoder(bytes, port) {
// Decode uplink message

//Ultrasound Distance Value
distance = (bytes[5]<<40 ) + (bytes[6]<<32 );

//Temperature
value = (bytes[8])
temp=value.toFixed(2)

//Payload Data Type
if (bytes[3] <= 0x2)

 return {
			DISTANCE:distance
			TEMPERATURE:temp		

} ;
}