Does “epsilon” really guarantees anything in floating-point computations?

Question

To make the problem short let\'s say I want to compute the expression a / (b - c) on floats.

To make sure the result is meaningful, I can ch

Answer 1

Epsilon is used to determine whether two numbers subject to rounding error are close enough to be considered "equal". Note that it is better to test fabs(b/c - 1) < EPS than fabs(b-c) < EPS, and even better — thanks to the design of IEEE floats — to test abs(*(int*)&b - *(int*)&c) < EPSI (where EPSI is some small integer).

Your problem is of a different nature, and probably warrants testing the result rather than the inputs.