Thanks, Neil! Why is the loop needed? I can't seem to get it to take more than one iteration.
Robby On Mon, May 12, 2014 at 11:24 PM, Neil Toronto <neil.toro...@gmail.com> wrote: > 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 >> >> >> > ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; >> >> >> >> >> ____________________ >> Racket Users list: >> http://lists.racket-lang.org/users >> > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
