private void upscale(int nbits) {
		unscaled = unscaled.shiftLeft(nbits);
		scale -= nbits;
	}
Return the BigFloat with the given number of bits representing (quiet) NaN.

@param fracbits number of fractional bits
@param expbits number of bits in the exponent
@param sign +1 or -1
@return a BigFloat representing (quiet) NaN
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/pcode/floatformat/BigFloat.java