Fibonacci sequence

<?php
declare(strict_types=1);

/*
 * The number of bytes in an integer determines the number of iterations that can be requested.
 * Once the computed value no longer fits in an integer, PHP will automatically convert to use
 * floating point representation, which means that the result is no longer accurate.
 * An alternative to imposing these limits would be to use the GNU MP library.
 */

function fibonacci(int $iterations): Generator
{
    if (
        $iterations <= 0
        || (PHP_INT_SIZE == 4 && $iterations > 47)  // max iterations for 32-bit int
        || $iterations > 92  // assume 64-bit int
    ) {
        throw new ValueError('Invalid number of iterations specified');
    }

    $num1 = 0;  // seed the initial values
    $num2 = 1;

    while ($iterations--) {
        yield $num1;

        $num2 = $num2 + $num1;
        $num1 = $num2 - $num1;
    }
}


foreach (fibonacci(10) as $number) {
    echo $number, ' ';
}