Re:Pretty.c
by aartaka on Thursday October 24, 2024 @07:10AM
(#41934338)
Indeed, FLT_EPSILON is not a one-size-fits-all solution, but it's good enough for frequent case of comparing big enough numbers, which is not covered by regular ==. So it's a convenience/correctness trade-off I'm ready to make.
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If the numbers you are comparing are greater than 2, abs(a - b) < FLT_EPSILON is equivalent to a == b. Because it's not possible for two large numbers to not be equal, but also closer together than FLT_EPSILON.
Re:Pretty.c
by jdthedisciple on Thursday October 24, 2024 @03:06PM
(#41938645)
what
// FLT_EPSILON == 0.01
equal(4.999, 5); // true
4.999 == 5; // false
FLT_EPSILON is not 0.01, it's 0.00000011920929.
But it's impossible to have a number that's 0.00000011920929 less than 5.0, or 0.00000011920929 more than 5.0, because the floats with enough magnitude to represent 5 are spaced further apart than that. Only numbers with magnitude < 2 are spaced close enough together.
In other words, the only 32-bit float that's within ±0.00000011920929 of 5.0 is 5.0 itself.
Re:Pretty.c
by jdthedisciple on Thursday October 24, 2024 @04:19PM
(#41939314)
Oh you're right, thanks for the explanation!
Gotta research now where the 0.00000011920929 number comes from...
It's the distance between 1.0 and the next representable float.
Re:Pretty.c
by jdthedisciple on Thursday October 24, 2024 @04:47PM
(#41939585)
I got that but I am curious how to derive that number.
Is it representable as a non-trivial ratio of integers?