Re: Float numbers equality.

[Leo Razoumov <slonik.az@...>]

On 8/9/13, Luiz Henrique de Figueiredo <lhf@tecgraf.puc-rio.br> wrote:
>> function float_equal(lhs, rhs, epsilon)
>>     return math.abs(lhs - rhs) < epsilon
>> end
>
> As mentioned before, if you have to do this, you need to use *relative*
> error,
> not absolute error:
>       return math.abs(lhs - rhs) < epsilon*rhs
>

The code above is incorrect for rhs <= 0.

It is better to try the following (untested):

function float_equal(lhs, rhs, epsilon)
    local abs= math.abs
    epsilon  = epsilon or 1E-12
    return abs(lhs - rhs) <= epsilon * (abs(lhs) + abs(rhs))
end

This implementation handles correctly the cases when one or both
numbers are zero or negative,
 and, (the added bonus) the function is symmetrical w.r.t. lhs<->rhs
substitutions.

--Leo--