public BigInteger opSub(BigInteger a, BigInteger b) { // a - b
		BigFloat fa = decodeBigFloat(a);
		BigFloat fb = decodeBigFloat(b);
		fa.sub(fb);
		return getEncoding(fa);
	}
Construct SmallFloat Data. (similar to BigFloat)

@param fracbits number of fractional bits (positive non-zero value; includes additional
           implied bit if relavent).
@param expbits maximum number of bits in exponent
@param kind the Kind, FINITE, INFINITE, ...
@param sign +1 or -1
@param unscaled the value's mantissa
@param scale value's scale
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/pcode/floatformat/FloatFormat.java