Re: floating point comparison

[dewar@merv.cs.nyu.edu (Robert Dewar)]

<<  However, it is true that if you know what is going on, and know what you
want that you might get away with it. But *I* would never write a code to
go into a life-critical system that had the line

if(a == b) return -1;

  Or the like, where a and b are floats.>>


There is zero justification for this statement. The general rule is
that you had better not write any floating-point operations in life
critical systems that have not been extremely carefully analyzed by
competent numerical analysis (many systems of rules for such systems
eliminate the use of floating-point completely for this reason).

If you are using floatingpoint in such a system, with proper analysis,
then it is entirely possible that this analysis may indicate not only
that an equality operation of the above type is acceptable, but it may

be correct where some kind of attempt at apprixmate testing would be
incorrect.

I canot imagine that anyone would think that simple (and incorrect) rules
such as the above would make it safe to employ floating-point 
calculations in life critical systems.