public long readNextValue(DataConverter dc, int len) throws IOException {
		long result = readValue(dc, currentIndex, len);
		currentIndex += len;
		return result;
	}
Returns the signed value of the integer (of the specified length) at the current index.

@param dc {@link BigEndianDataConverter BE} or {@link LittleEndianDataConverter LE}
@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