[racket] "error: degrees->complex: 360.0"

He went with exact rationals. Here's another option, which preserves 
inexactness:

     (define (angle->proper-range α)
       (let loop ([θ  (- α (* 360 (floor (/ α 360))))])
         (cond [(negative? θ)  (loop (+ θ 360))]
               [(>= θ 360)     (loop (- θ 360))]
               [else  θ])))

Its accuracy drops off outside of about [-1e16,1e16].

The fact that this is hard to get right might be good motivation for an 
`flmodulo` function.

Neil ⊥

On 05/12/2014 09:49 PM, Sean Kanaley wrote:
> Interesting, my code has the same bug then.  I called it modulo/real,
> used for things like displaying the space ship's rotation to the user or
> wrapping x coordinates to stay in the world.  Apparently it's going to
> fail at some point with vector ref out of range.  What was your fix?  I
> was thinking to just clamp explicitly like mod/real = (max 0 (min
> the-mod-minus-1 (old-modulo/real x)))
>
>
> On Mon, May 12, 2014 at 11:12 PM, Robby Findler
> <robby at eecs.northwestern.edu <mailto:robby at eecs.northwestern.edu>> wrote:
>
>     Right. Probably there is a better fix, but the essential problem, as I
>     understand it, is that there are more floating points between 0 and 1
>     than between any two other integers and the code made the assumption
>     that that didn't happen....
>
>     The basic desire is to turn a real number into a number in [0,360)
>     such that the result represents the same number in degrees but is
>     normalized somehow.
>
>     Robby
>
>     On Mon, May 12, 2014 at 10:06 PM, Danny Yoo <dyoo at hashcollision.org
>     <mailto:dyoo at hashcollision.org>> wrote:
>      > Wow.  Floating point really is nasty.  I see how it might have
>     happened now.
>      >
>      > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>      >> -0.0000000000000001
>      > -1e-16
>      >> (+ 360 -1e-16)
>      > 360.0
>      >>
>      > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>
>
>
>
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