Unexpected loss of precision when dividing doubles

Question

I have a function getSlope which takes as parameters 4 doubles and returns another double calculated using this given parameters in the following way:

double QSw         


        

Answer 1

Better Print out the arguments, too. When you are, as I guess, transferring parameters in decimal notation, you will lose precision for each and every one of them. The problem being that 1/5 is an infinite series in binary, so e.g. 0.2 becomes .001001001.... Also, decimals are chopped when converting an binary float to a textual representation in decimal.

Next to that, sometimes the compiler chooses speed over precision. This should be a documented compiler switch.