add_filter( 'woocommerce_sale_flash2', 'lx_custom_onsale_label', 10, 2 );
  function lx_custom_onsale_label() {
    global $product;

    $percentage = round( ( ( $product->get_regular_price()  - $product->get_sale_price() ) / $product->get_regular_price()  ) * 100 );
    $absolute = round( ( ( $product->get_regular_price()  - $product->get_sale_price() ) ) );

    if ($product->get_regular_price()  > 100) {
    return '<span class="onsalex bg_primary headerfont">'. sprintf( __(' -%s', 'salex' ), $absolute . ',-' ).'</span>';
    }

    else if ($product->get_regular_price()  < 1) {
    return '<span class="onsalessszzzx bg_primary headerfont">'. sprintf( __(' -%s', 'salex' ), $absolute . ',-' ).'</span>';
    }

    else {
    return '<span class="onsalexzzz bg_primary headerfont">'. sprintf( __(' -%s', 'salex' ), $percentage . '%' ).'</span>';
    }
}

$percentage = round( ( ( $product->get_regular_price()  - $product->get_sale_price() ) / $product->get_regular_price()  ) * 100 );

$percentage = round( ( ( $product->get_regular_price()  - $product->get_sale_price() ) / $product->get_regular_price()  ) * 100 );

$percentage = 0;
if ( $product->get_regular_price() > 0 )
    $percentage = round( ( ( $product->get_regular_price()  - $product->get_sale_price() ) / $product->get_regular_price()  ) * 100 );

if ($product->get_regular_price() != 0){
  // Do stuff
} else {
  // Do something with the zero
}

if ($product->get_regular_price() > 0){
  // Do stuff
} else {
  // Do something with the zero
}

if($product->get_regular_price()> 0)
{
//do your work
}

$var = @($val1 / $val2);