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
<ro...@eecs.northwestern.edu <mailto:ro...@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 <d...@hashcollision.org
<mailto:d...@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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