Swap variables XOR

swap_var_xor.php

<?php

// Swap these two variables.
$a = 13;
$b = 72;
print_r(compact('a', 'b'));

// Now swap in a "memory efficient" way.
$a ^= $b;
$b ^= $a;
$a ^= $b;
print_r(compact('a', 'b'));

// Now swap again using array.
[$a, $b] = [$b, $a];
print_r(compact('a', 'b'));

// Now swap using temporary variable.
$tmp = $b;
$b = $a;
$a = $tmp;
print_r(compact('a', 'b'));

$j = 500000000;

// Benchmark method 1.
$a = 13;
$b = 72;
memory_reset_peak_usage();
$sec_init = time();
$i = $j;
while (--$i) {
    $a ^= $b;
    $b ^= $a;
    $a ^= $b;
}
printf("Mem: %s, Time: %s, Method xor\n", memory_get_peak_usage(), time()-$sec_init);

// Benchmark method 2.
$a = 13;
$b = 72;
memory_reset_peak_usage();
$sec_init = time();
$i = $j;
while (--$i) {
    [$a, $b] = [$b, $a];
}
printf("Mem: %s, Time: %s, Method des\n", memory_get_peak_usage(), time()-$sec_init);

// Benchmark method 3.
$a = 13;
$b = 72;
memory_reset_peak_usage();
$sec_init = time();
$i = $j;
while (--$i) {
    $tmp = $b;
    $b = $a;
    $a = $tmp;
}
printf("Mem: %s, Time: %s, Method tmp\n", memory_get_peak_usage(), time()-$sec_init);

// Mem: 419408, Time: 10, Method xor
// Mem: 419624, Time: 24, Method des
// Mem: 419408, Time: 6, Method tmp