Validation sum of input

hello

i want to validate sum of input array equal 100

if i post form with this value : 
blanc : 30
brun : 50
cuisine : 60
informatique : 70
telephonie : 80
autre : 90
if sum not equal 100, i send an error, i must have 100


html : 

Code:

<div class="tab-cell w50prc">
    <label class="spe"><span>*</span> Répartition activité :</label>
    <p class="inline-block w50prc"><input type="text" placeholder="% Blanc" name="repartition[blanc]" id="repartition[blanc]" value="(-$infos.blanc-)"></p>
    <p class="inline-block w50prc"><input type="text" placeholder="% Brun" name="repartition[brun]" id="repartition[brun]" value="(-$infos.brun-)"></p>
    <p class="inline-block w50prc"><input type="text" placeholder="% Cuisine" name="repartition[cuisine]" id="repartition[cuisine]" value="(-$infos.cuisine-)"></p>
    <p class="inline-block w50prc"><input type="text" placeholder="% Informatique" name="repartition[informatique]" id="repartition[informatique]" value="(-$infos.informatique-)"></p>
    <p class="inline-block w50prc"><input type="text" placeholder="% Téléphonie" name="repartition[telephonie]" id="repartition[telephonie]" value="(-$infos.telephonie-)"></p>
    <p class="inline-block w50prc"><input type="text" placeholder="% Autre" name="repartition[autre]" id="repartition[autre]" value="(-$infos.autre-)"></p>
</div>

PHP Code:

$this->ci->form_validation->set_rules('repartition[]', 'répartitions', 'trim|callback_checkTotalRepartitionsTest[repartition]'); 


This works but the test is performed 6 times, which is not good

PHP Code:

   public function checkTotalRepartitionsTest($str,$field){
        if(array_sum($_POST[$field])<>100){
            return FALSE;
        }
    } 


thanks