On Thu, Apr 26, 2018 at 1:17 AM, Yuval Lifshitz <yuva...@gmail.com> wrote:
>
> I ran into the following issue when started playing with go. Had the
> following small program to calculate Fibonacci numbers using the closed
> form:
>
> package "fib"
>
> import "math"
>
> var sqrt_5 = math.Sqrt(5.0)
> var psi = -1.0/math.Phi
>
> // had to add this to solve accuracy issue
> func round(x float64) uint64 {
> return uint64(math.Floor(x + 0.5))
> }
>
> // find the nth fibonacci number based on Binet's formula
> // see here:
> https://en.wikipedia.org/wiki/Fibonacci_number#Closed-form_expression
> func fibonacci(n uint) uint64 {
> float_n := float64(n)
> return round((math.Pow(math.Phi, float_n) - math.Pow(psi,
> float_n))/sqrt_5)
> }
>
>
> When I first tried without doing the "rounding" I did not get whole numbers
> as the output (similar program in C++ gave whole numbers without rounding).
> Following test is failing without the call to "round()":
>
> package "fib"
>
> import "testing"
>
> var results = map[uint]uint64 {
> 0: 0,
> 2: 1,
> 10: 55,
> 14: 377,
> 20: 6765,
> 29: 514229,
> 33: 3524578,
> 59: 956722026041,
> }
>
> func Test_fibonacci(t *testing.T) {
> for arg, expected := range results {
> actual := fibonacci(arg)
> if actual != expected {
> t.Error("Expected", expected, "got", actual)
> }
> }
> }
>
>
>
> Are there known accuracy issues with floating points in go?
No.
I suggest that you show us your C code. Thanks.
Ian
--
You received this message because you are subscribed to the Google Groups
"golang-nuts" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to golang-nuts+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
