Simple PHP helper functions to generate five-star rating stars.

star-rating-v1.php

<?php

/**
 * Example: five_star_rating_stars(4.8);
 *          five_star_rating_stars(
 *              4.8,
 *              '<i class="fas fa-star"></i>',
 *              '<i class="fas fa-star-half-alt"></i>',
 *              '<i class="far fa-star"></i>'
 *          );
 */

if (! function_exists('five_star_rating_stars')) {
    function five_star_rating_stars(float $raw_rating, $filled_star = '★', $half_star = '⯪', $empty_star = '☆')
    {
        $highest_rating = 5;

        if ($raw_rating < 0 || $raw_rating > $highest_rating) {
            return false;
        }

		// map rating scores to *.5 or *.0
		// see https://stackoverflow.com/a/19050089/10468523
        $rating = round($raw_rating * 2) / 2;

		// https://stackoverflow.com/a/6619392/10468523
        $whole = (int) floor($rating);

        // append filled star(s)
        $all_five_stars = str_repeat($filled_star, $whole);

        if ($whole === $highest_rating) {
            return $all_five_stars;
        }

        $fraction = $rating - $whole;
        $counter = $highest_rating - $whole;

        // append half star
        if ($fraction === 0.5) {
            $all_five_stars .= $half_star;
            --$counter;
        }

        // append empty star(s)
        while ($counter > 0) {
            $all_five_stars .= $empty_star;
            --$counter;
        }

        return $all_five_stars;
    }
}

star-rating-v2.php

<?php

/**
 * Example: $rating = mround(4.8, 0.5);
 *          five_star_rating_stars($rating);
 */

if (! function_exists('same_sign_float')) {
    function same_sign_float(float $x, float $y)
    {
        return ($x > 0 && $y > 0) || ($x < 0 && $y < 0);
    }
}

// Try to create a function equivalent to Microsoft Excel MROUND function
// https://support.microsoft.com/en-us/office/mround-function-c299c3b0-15a5-426d-aa4b-d2d5b3baf427
if (! function_exists('mround')) {
    function mround(float $number, float $multiple)
    {
        if (! same_sign_float($number, $multiple)) {
            return false;
        }

        // https://stackoverflow.com/a/48643210/10468523
        return round($number / $multiple, 0, PHP_ROUND_HALF_UP) * $multiple;
    }
}

if (! function_exists('five_star_rating_stars')) {
    function five_star_rating_stars(float $rating, $full_star_sign = '★', $half_star_sign = '⯪', $empty_star_sign = '☆') {
        $highest_rating = 5;

        if ($rating < 0 || $rating > $highest_rating) {
            return false;
        }

        // https://developer.wordpress.org/reference/functions/wp_star_rating/
        $full_star_number = floor($rating);
        $half_star_number = ceil($rating - $full_star_number);
        $empty_star_number = $highest_rating - $full_star_number - $half_star_number;

        $stars = str_repeat($full_star_sign, $full_star_number);
        $stars .= str_repeat($half_star_sign, $half_star_number);
        $stars .= str_repeat($empty_star_sign, $empty_star_number);

        return $stars;
    }
}