I was playing with a regex that determines whether a string contains a square number of characters. I have the following program:

#!/usr/bin/perl

use strict;
use warnings;

my $MAX = 100;

my $re = qr /^(1+)(??{"(?:$1){" . (length ($1) - 1) . "}" })$/;

for (1 .. $MAX)
    {printf "%3d is a square\n" => $_ if (1 x $_) =~ /$re/}
do  {printf "%3d is a square\n" => $_ if (1 x $_) =~ /$re/} for 1 .. $
+MAX;
map {printf "%3d is a square\n" => $_ if (1 x $_) =~ /$re/}     1 .. $
+MAX;
[download]

If I run this, it dies:

  1 is a square
  4 is a square
  9 is a square
 16 is a square
 25 is a square
 36 is a square
 49 is a square
 64 is a square
 81 is a square
100 is a square
  1 is a square
  4 is a square
  9 is a square
 16 is a square
 25 is a square
 36 is a square
 49 is a square
 64 is a square
 81 is a square
100 is a square
  1 is a square
  4 is a square
  9 is a square
 16 is a square
 25 is a square
 36 is a square
 49 is a square
Out of memory!
[download]

If I outcomment the map, it runs fine. If I lower $MAX to 70, it runs fine. If I lower $MAX to 70, and move the map statement to just before the for BLOCK, it dies as well:

  1 is a square
  4 is a square
  9 is a square
 16 is a square
 25 is a square
 36 is a square
 49 is a square
 64 is a square
Out of memory!
[download]

If I increase $MAX to 200, the program runs fine, regardless where the map is.

My OS tools (ps, top, /proc, vmstat) don't indicate any abnormal memory usuage from the program, nor does any swapping to disk occur.

Am I doing something stupid without seeing it, or did I hit a bug in Perl?

Abigail

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