public long readValue(DataConverter dc, long index, int len) throws IOException {
		byte[] bytes = provider.readBytes(index, len);
		return dc.getSignedValue(bytes, len);
	}
Returns the signed value of the integer (of the specified length) at the specified offset.

@param dc {@link BigEndianDataConverter BE} or {@link LittleEndianDataConverter LE}
@param index where the value begins 
@param len the number of bytes that the integer occupies, 1 to 8
@return value of requested length, with sign bit extended, in a long
@exception IOException if an I/O error occurs
Ghidra/Features/Base/src/main/java/ghidra/app/util/bin/BinaryReader.java