OpenEuphoria

RE: logs and antilogs

• Posted by Andy Serpa <ac at onehorseshy.com> Oct 26, 2002
• 482 views

Kat wrote:
> I have been looking all over the net for a formula to calculate logs and 
> 
> antilogs for any given number, but turned up zip. Can anyone suggest a 
> formula?
> 
> Kat
> 
> 

Found this on web, and translated to Euphoria:

-- natural logarithm
function ln(atom x)
atom precision,l,m,n,k,val

    if x <= 0.0 then
        -- ERROR: can't take a log of zero or negative
        -- return some appropriate error here (like a sequence)
        -- or kill program
    end if

    precision = 1e-15

    m = 1.0

    n = 0.0
    while (x/m >= 10.0) do
        m *= 10.0
        n += 1.0
    end while

    if x < 1.0 then
        n = 0.0
        while (x/m <= 0.1) do
            m *= 0.1
            n -= 1.0
        end while
    end if

    x /= m
    x = (x-1)/(x+1)
    l = x
    val = x


    k = 3.0

    l *= x*x
    m = l/k
    val += m

    if m < 0.0 then
        m = -m
    end if

    while (m >= precision) do
        k += 2.0
        l *= x*x
        m = l/k
        val += m

        if m < 0.0 then
            m = -m
        end if
    end while

    val = (val * 2) + (n*2.30258509298749)

    return val --  / 2.30258509298749 (uncomment to get log10)

end function


-- returns base-based logarithm of x
function logbase(atom x, atom base)
    return ln(x)/ln(base)
end function