Re: comparing doubles for equality

John Smith wrote:
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?
Depending on how you use this, you could make your application highly dependent on external issues, such as whether you compile for an extra precision mode, or disable gradual underflow.
.

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