Re^4: Extraction of List of Coordinates

After compensating for everything I could think of, XOR still won. Surprisingly, it won against the standard temp-variable swap. Incredibly, it won against a sub that simply returned the numbers in reverse order (in fact, temp swapping generally beat that, too!). I could only think that it wins because the integer math makes things simpler internally.

I tried different types of arguments, and preprocessing the argument list to force it to integer. Speedup was slight, if there was any at all, for the integer-forced versions. Perl swapping lost pretty consistently in all cases. Temp swapping and return-value swapping beat XOR for swapping strings, sometimes. I got inconsistent results.

Benchmark code follows...

use Benchmark 'cmpthese';

my @swapthese;

sub xor_swap {
  my ($x,$y)=@swapthese;
  $x ^= $y; $y ^= $x; $x ^= $y;
  ($x,$y);
}

sub perl_swap {
  my ($x,$y)=@swapthese;
  ($x,$y) = ($y,$x);
  ($x,$y);
}

sub perl_i_swap {
  my ($x,$y)=@swapthese;
  ($x,$y) = ($y^0,$x^0);
  ($x,$y);
}

{
  my $tmp;
  sub tmp_swap {
    my ($x,$y)=@swapthese;
    $tmp=$x; $x=$y; $y=$tmp;
    ($x,$y);
  }

  sub tmp_i_swap {
    my ($x,$y)=@swapthese;
    $tmp=$x^0; $x=$y^0; $y=$tmp;
    ($x,$y);
  }

}

sub ret_swap {
  my ($x,$y)=@swapthese;
  ($y,$x);
}

sub ret_i_swap {
  my ($x,$y)=@swapthese;
  $x ^= 0; $y ^= 0;
  ($y,$x);
}

for my $S ([38,970], [38.1,970], ['foo',38], ['foo','barbell']) {
  @swapthese = @$S;

print "Swapping @swapthese\n";
print "XOR: @{[xor_swap()]}\n";
print "Perl: @{[perl_swap()]}\n";
print "Perl I: @{[perl_i_swap()]}\n";
print "TMP: @{[tmp_swap()]}\n";
print "TMP I: @{[tmp_i_swap()]}\n";
print "RET: @{[ret_swap()]}\n";
print "RET I: @{[ret_i_swap()]}\n";

cmpthese (-2, {
    xor_swap  => \&xor_swap,
    perl_swap => \&perl_swap,
    tmp_swap  => \&tmp_swap,
    ret_swap  => \&tmp_swap,
    perl_i_swap => \&perl_swap,
    tmp_i_swap  => \&tmp_swap,
    ret_i_swap  => \&tmp_swap,
});
}
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Caution: Contents may have been coded under pressure.

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