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Queue.copy is not tail recursive ! #4079

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vicuna opened this issue Aug 7, 2006 · 1 comment
Closed

Queue.copy is not tail recursive ! #4079

vicuna opened this issue Aug 7, 2006 · 1 comment
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@vicuna
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@vicuna vicuna commented Aug 7, 2006

Original bug ID: 4079
Reporter: Christophe
Assigned to: @gasche
Status: closed (set by @xavierleroy on 2015-12-11T18:19:47Z)
Resolution: fixed
Priority: normal
Severity: minor
Version: 3.09.2
Target version: 4.00.2+dev
Category: standard library
Monitored by: @mmottl

Bug description

Queue.copy is not tail recursive. Hence, large queue can not be safely duplicated.
This would be very simple to make it tail-recursive. I propose here a solution ;

let copy q =
if q.length = 0 then
create()
else
let tail = q.tail in

let rec tail' = {
  content = tail.content;
  next = tail'
} in

let rec copy prev cell =
  if cell != tail 
  then let res = {
    content = cell.content;
    next = tail'
  } in prev.next <- res; 
  copy res cell.next in

copy tail' tail.next;
{ 
  length = q.length;
  tail = tail'
}
@vicuna
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@vicuna vicuna commented Jun 16, 2013

Comment author: @gasche

I reviewed the patch and observed good performance results (even on smallish queues). Applied, as is, to 4.01 and trunk.

@vicuna vicuna closed this Dec 11, 2015
@vicuna vicuna added the stdlib label Mar 14, 2019
@vicuna vicuna added this to the 4.00.2 milestone Mar 14, 2019
@vicuna vicuna added the bug label Mar 19, 2019
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