in_array() vs array_key_exists()

result.txt

Time shows total time for 1024 iterations

Size    | in_array | array_key_exists
      1 |    0.000 | 0.000
      2 |    0.001 | 0.000
      4 |    0.001 | 0.000
      8 |    0.001 | 0.001
     16 |    0.001 | 0.000
     32 |    0.001 | 0.000
     64 |    0.001 | 0.000
    128 |    0.002 | 0.001
    256 |    0.003 | 0.000
    512 |    0.007 | 0.001
   1024 |    0.013 | 0.001
   2048 |    0.030 | 0.000
   4096 |    0.048 | 0.001
   8192 |    0.079 | 0.001
  16384 |    0.140 | 0.001
  32768 |    0.181 | 0.001

test.php

<?php

echo "Time shows total time for 1024 iterations\n\n";
echo "Size    | in_array | array_key_exists\n";
for ($size = 1; $size <= 32768; $size *= 2) {

    $a = [];
    for ($i = 0; $i < $size; ++$i) {
        $a[] = $i;
    }
    $start = microtime(true);
    for ($i = 0; $i < 1024; ++$i) {
        in_array($i * 32, $a);
    }
    $time1 = microtime(true) - $start;

    $a = [];
    for ($i = 0; $i < $size; ++$i) {
        $a[$i] = 1;
    }
    $start = microtime(true);
    for ($i = 0; $i < 1024; ++$i) {
        array_key_exists($i * 32, $a);
    }
    $time2 = microtime(true) - $start;

    printf("%7d | %8.3f | %.3f\n", $size, $time1, $time2);
}