[WooCommerce BR] Woocommerce - show discount percentage

functions.php

<?php

add_filter( 'woocommerce_sale_flash', function( $string, $post, $product ) {

    $regular_price = (float) $product->get_regular_price();
    $sale_price = (float) $product->get_price();

    $discount = round( 100 - ( $sale_price / $regular_price * 100 ), 1 );

    return sprintf( '<span class="onsale">%s%%</span>', $discount );

}, 10, 3 );