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Re: in-place reverse?

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On 22/10/21 5:24 pm, luser droog wrote:
> I was reading through some old code and found this function to
> reverse an array.
> ...
> And I wondered if it were possible to do it in-place, without creating
> a new array.

My first idea was this:

   /reverse  {
     dup aload
     0 1 2 index length 1 sub {
       1 index exch 4 -1 roll put
     } for
     pop
   } bind def

It works, is fast, but uses a lot of stack if the array is large.

So I came up with this, which uses minimal stack and gives similar 
performance (when bound):

   /reverse {
     dup xcheck exch
     dup length 1 sub
     0 1 3 index length 2 idiv 1 sub {
       2 index exch
       1 index 3 index get
       2 index 4 index 1 index 4 index get put
       put
       1 sub
     } for
     pop
     exch {cvx} if
   } bind def

By the way, I liked the xcheck.  Obviously that's something I borrowed.

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in-place reverse? luser droog <luser.droog@gmail.com> - 2021-10-21 23:24 -0700
  Re: in-place reverse? luser droog <luser.droog@gmail.com> - 2021-10-22 17:13 -0700
    Re: in-place reverse? luser droog <luser.droog@gmail.com> - 2021-10-22 17:42 -0700
    Re: in-place reverse? luser droog <luser.droog@gmail.com> - 2021-10-23 16:54 -0700
  Re: in-place reverse? luser droog <luser.droog@gmail.com> - 2021-10-22 17:16 -0700
  Re: in-place reverse? James <news@oxdrove.co.uk> - 2021-10-24 11:04 +0100
    Re: in-place reverse? luser droog <luser.droog@gmail.com> - 2021-10-24 17:59 -0700
    Re: in-place reverse? luser droog <luser.droog@gmail.com> - 2021-11-08 10:08 -0800
  Re: in-place reverse? David Newall <davidn@davidnewall.com> - 2022-01-21 21:10 +1100
    Re: in-place reverse? luser droog <luser.droog@gmail.com> - 2022-01-21 21:22 -0800
      Re: in-place reverse? jdaw1 <jdawiseman@gmail.com> - 2022-08-10 13:11 -0700

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