<?php
        $helper  = Mage::helper('warehouse');
        $productHelper = Mage::helper('warehouse/catalog_product');
        $stockIds = $helper->getStockIds();

        $qty = 0;

        foreach ($stockIds as $stockId) {
            $qty = $qty + $productHelper->getQuoteMaxQty($_product, $stockId);
        }?>

class Amasty_Feed_Model_Attribute_Compound_Qty extends Amasty_Feed_Model_Attribute_Compound_Abstract
{
    function prepareCollection($collection){
        $collection->joinQty();
    }

    function getCompoundData($productData){
        return $productData['qty'];
    }

    function hasCondition(){
        return true;
    }

    function prepareCondition($collection, $operator, $condVal, &$attributesFields){
        $collection->joinQty();

        $attributesFields[] = array(
            'attribute' => 'qty',
            $operator => $condVal
        );
    }

    function hasFilterCondition(){
        return true;
    }

    function validateFilterCondition($productData, $operator, $valueCode){
        return Amasty_Feed_Model_Field_Condition::compare($operator, $productData['qty'], $valueCode);
    }
}