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In prestashop 1.7 I have declared products discount in amount and not in percentage.

But in product page i want to show the corresponding percentage instead of the discount amount.
The lines of code that show a percentage or amount of discount depending on what you put in the admin are:
 

 <!-- {if $product.discount_type === 'percentage'}
                  <span class="discount-percentage discount-product">{$product.discount_percentage}</span>
                {elseif $product.discount_type === 'amount'}
                  <span class="discount-amount discount-product">{$product.discount_amount_to_display}</span>
                {/if} -->

Any idea how i can calculate the discount rate from the discount amount and show it in place of discount amount?