[exDM69]

Yes, this is by design and it works as intended.

I typically use this with doubles and DBL_EPSILON, which is much much smaller than FLT_EPSILON.

With FLT_EPSILON this roughly equals to "zero" being "less than 0.001". If the zero check is omitted, there's going to be a division by near-zero which will make the results nonsense (and you have to draw the line somewhere). With DBL_EPSILON "zero is less than 0.000000001".

If this is too loose, then `zero(x) = abs(x) < FLT_EPSILON` makes it much stricter (about 1e-7).

This is good enough for my purposes, I don't deal with very small numbers in float and doubles give more than enough precision.

NOTE: I usually use this kind of comparison in testing by comparing known "gold" figures against the results of the code being tested. I don't test accuracy, I test for "in the ballpark" because the stuff I deal with has built-in inaccuracy in the algorithm and numerics.

The version you posted will always return false if I read it correctly.