Re: comparing doubles for equality

In article <I8Clh.533642$1T2.401780@pd7urf2no> John Smith <JSmith@xxxxxxxx> writes:
This code for the comparison of fp types is taken from the C FAQ.
Any problems using it in a macro?

/* compare 2 doubles for equality */
#define DBL_ISEQUAL(a,b) (fabs((a)-(b))<=(DBL_EPSILON)*fabs((a)))

Do the same issues involved in comparing 2 fp types for equality
apply to comparing a float to zero? E.g. is if(x == 0.0)
considered harmful?

If you insert 0.0 for 'a' you will see that the two give precisely the
same result. On the other hand, I think it is possible to construct
two floating point numbers 'a' and 'b', where the result is asymmetric.
But let that not deter you from using the macro, when it is asymmetric
you are in the outskirts of floating-point arithmetic.
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