PHP Program to Count Primes in Ranges

<?php
// PHP program to answer queries for 
// count of primes in given range.

$MAX = 10000;

// prefix[i] is going to
// store count of primes
// till i (including i).
$prefix = array_fill(0, ($MAX + 1), 0);

function buildPrefix() {
    global $MAX, $prefix;
    
    // Create a boolean array value in
    // prime[i] will "prime[0..n]". A 
    // finally be false if i is Not a
    // prime, else true.
    $prime = array_fill(0, ($MAX + 1), true);

    for ($p = 2; $p * $p <= $MAX; $p++)  {

        // If prime[p] is not changed, 
        // then it is a prime
        if ($prime[$p] == true){

            // Update all multiples of p
            for ($i = $p * 2; 
                 $i <= $MAX; $i += $p)
                $prime[$i] = false;
        }
    }

    // Build prefix array
    // $prefix[0] = $prefix[1] = 0;
    for ($p = 2; $p <= $MAX; $p++) {
        $prefix[$p] = $prefix[$p - 1];
        if ($prime[$p])
            $prefix[$p]++;
    }
}

// Returns count of primes 
// in range from L to
// R (both inclusive).
function query($L, $R) {
    global $prefix;
    return $prefix[$R] -
           $prefix[$L - 1];
}

// Driver code
buildPrefix();

$L = 5;
$R = 10;
echo query($L, $R) . "\n";

$L = 1;
$R = 10;
echo query($L, $R);

?>