sub number_format {
   my $num = shift;
   return $num unless $num;
   return undef unless $num =~ /^[0-9\.+-]+$/;
   $num =~ s/^([\+-])?//;
   my $sign = $1;
   $num =~ s/\.([0-9]+)$//;   # must come before the call to abs(), be
+cause here
   my $dec = $1;              # a floating point value is still regard
+ed as a string by perl, even if it's 0.00.
   $num = abs $num;
   $num = reverse $num;
   $num =~ s/(\d{3})/$1\,/g;
   $num =~ s/\.$//;
   $num = reverse $num;
   $num .= ".$dec" if $dec;
   $num = "$sign$num" if $sign;
   $num;
}
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