WooCommerce: swap sale and regular pricing display

swap_regular_and_sale_prices.php

<?php
add_filter( 'woocommerce_get_price_html', 'my_price_html', 100, 2 );
function my_price_html( $price, $product ){
    // swap the regular and sale prices
    $pos_start = strpos($price, '<del>');
    if ($pos_start !== false) {
        $end = '</del>';
        $end_length = strlen($end);
        $pos_end_start = strpos($price, $end);
        $pos_end = $pos_end_start + $end_length;
        $regular_price = substr($price, $pos_start, $pos_end);
        $price_length = strlen($price);
        $sale_price = substr($price, $pos_end + 1, $price_length);
        return $sale_price . $regular_price;
    }
    return $price;
}