PHP Activist

Lessons learned:

• HHVM runs recursive function calls 13-20 times faster than PHP
• HHVM runs recursive function calls 25-50 percent slower than Javascript
• HHVM runs recursive function calls 4-5 times slower than Java
• HHVM runs recursive function calls 2-8 times slower than C

Here is a sample script using the Ackermann function:

<?php

function ack($n, $m) {
  if ($n == 0) return $m + 1;
    else if ($m == 0) return ack($n - 1, 1);
    else return ack($n - 1, ack($n, $m - 1));
}

function ack_while($n, $m) {
  while ($n != 0) {
    if ($m == 0) $m = 1;
      else $m = ack_while($n, $m - 1);
    $n--;
  }
  return $m + 1;
}

$start = microtime(true);
ack_while(3, 7);
echo number_format(microtime(true)-$start, 4).'s'.PHP_EOL;

$start = microtime(true);
ack(3, 7);
echo number_format(microtime(true)-$start, 4).'s'.PHP_EOL;

Here is a sample script using the Fibonacci function:

<?php

function fib_it($n) {
  $a = 0;
  $b = 1;
  for ($i = 0; $i < $n; $i++){
    $sum = $a+$b;
    $a = $b;
    $b = $sum;
  }
  return $a;
}

function fib_rec($n) {
  if ($n < 3) return 1;
  return fib_rec($n - 1) + fib_rec($n - 2);
}

$start = microtime(true);
fib_it(38);
echo number_format(microtime(true)-$start, 4).'s'.PHP_EOL;

$start = microtime(true);
fib_rec(38);
echo number_format(microtime(true)-$start, 4).'s'.PHP_EOL;

Running ack(3, 7) with PHP 5.4.4, 64bit, 2.3GHz (QEMU):

0.1127s
0.1794s

Running ack(3, 7) with HHVM 3.0/2014.03.27:

0.0089s
0.0141s

Running ack(3, 7) with Javascript (node.js v0.10):

0.013s
0.009s

Running ack(3, 7) with Java (OpenJDK 1.6 64bit):

0.011s
0.006s

Running ack(3, 7) with C (gcc 4.7):

0.002s

Running ack(3, 10) with PHP:

8.6962s
14.8648s

Running ack(3, 10) with HHVM:

Fatal error: Stack overflow in ack.php on line 12

Running ack(3, 10) with Javascript:

0.374s
0.595s

Running ack(3, 10) with Java:

0.077s
0.155s

Running ack(3, 10) with C:

0.085s

Running ack(3, 11) with PHP:

32.4175s
63.0294s

Running ack(3, 11) with HHVM:

Fatal error: Stack overflow in ack.php on line 12

Running ack(3, 11) with Javascript:

RangeError: Maximum call stack size exceeded

Running ack(3, 11) with Java:

0.314s
0.612s

Running ack(3, 11) with C:

0.339s

Running fib(38) with PHP 5.4.4, 64bit, 2.3GHz (QEMU):

0.0000s
14.6734s

Running fib(38) with HHVM 3.1/2014.04.09:

0.0032s
0.7149s

Running fib(38) with Javascript:

0.008s
0.572s

Running fib(38) with Java:

0.0s
0.158s

Running fib(38) with C:

0.092s

ack.c (run: gcc -O3 -o ack.out ack.c && time ./ack.out)

unsigned int ack(unsigned int n, unsigned int m) {
  if (n == 0) return m + 1;
    else if (m == 0) return ack(n - 1, 1);
    else return ack(n - 1, ack(n, m - 1));
}

unsigned int ack_while(unsigned int n, unsigned int m) {
  while (n != 0) {
    if (m == 0) {
      m = 1;
    } else {
      m = ack_while(n, m - 1);
    }
    n--;
  }
  return m + 1;
}

int main(int argc, char* argv[]) {
  ack_while(3, 7);
  ack(3, 7);
}

fib.c (run: gcc -O3 -o fib.out fib.c && time ./fib.out)

unsigned int fib_it(unsigned int n) {
  unsigned int a = 0;
  unsigned int b = 1;
  unsigned int sum;
  unsigned int i;
  for (i = 0; i < n; i++){
    sum = a + b;
    a = b;
    b = sum;
  }
  return a;
}

unsigned int fib_rec(unsigned int n) {
  if (n < 3) return 1;
  return fib_rec(n - 1) + fib_rec(n - 2);
}

int main(int argc, char* argv[]) {
  fib_it(38);
  fib_rec(38);
}

ack.js (run: time nodejs ack.js)

function ack(n, m) {
  if (n == 0) return m + 1;
    else if (m == 0) return ack(n - 1, 1);
    else return ack(n - 1, ack(n, m - 1));
}

function ack_while(n, m) {
  while (n != 0) {
    if (m == 0) {
      m = 1;
    } else {
      m = ack_while(n, m - 1);
    }
    n--;
  }
  return m + 1;
}

var start = new Date().getTime();
ack_while(3, 7);
console.log((new Date().getTime() - start) / 1000 + 's');

start = new Date().getTime();
ack(3, 7);
console.log((new Date().getTime() - start) / 1000 + 's');

fib.js (run: time nodejs fib.js)

function fib_it(n) {
  var a = 0;
  var b = 1;
  var sum = 0;
  for (var i = 0; i < n; i++){
    sum = a + b;
    a = b;
    b = sum;
  }
  return a;
}

function fib_rec(n) {
  if (n < 3) return 1;
  return fib_rec(n - 1) + fib_rec(n - 2);
}

var start = new Date().getTime();
fib_it(38);
console.log((new Date().getTime() - start) / 1000 + 's');

start = new Date().getTime();
fib_rec(38);
console.log((new Date().getTime() - start) / 1000 + 's');

ack.java (run: javac -g:none ack.java && java ack)

public class ack {
  public static int ack(int n, int m) {
    if (n == 0) return m + 1;
      else if (m == 0) return ack(n - 1, 1);
      else return ack(n - 1, ack(n, m - 1));
  }

  public static int ack_while(int n, int m) {
    while (n != 0) {
      if (m == 0) {
        m = 1;
      } else {
        m = ack_while(n, m - 1);
      }
      n--;
    }
    return m + 1;
  }

  public static void main(String[] args) throws Exception {
    long start = System.currentTimeMillis();
    ack_while(3, 7);
    System.out.println((float) (System.currentTimeMillis() - start) / 1000);

    start = System.currentTimeMillis();
    ack(3, 7);
    System.out.println((float)(System.currentTimeMillis() - start) / 1000);
  }
}

fib.java (run: javac -g:none fib.java && java fib)

public class fib {
  public static int fib_it(int n) {
    int a = 0;
    int b = 1;
    int sum;
    for (int i = 0; i < n; i++){
      sum = a + b;
      a = b;
      b = sum;
    }
    return a;
  }

  public static int fib_rec(int n) {
    if (n < 3) return 1;
    return fib_rec(n - 1) + fib_rec(n - 2);
  }

  public static void main(String[] args) throws Exception {
    long start = System.currentTimeMillis();
    fib_it(38);
    System.out.println((float) (System.currentTimeMillis() - start) / 1000);

    start = System.currentTimeMillis();
    fib_rec(38);
    System.out.println((float)(System.currentTimeMillis() - start) / 1000);
  }
}