Change the database quantity related fields type to DECIMAL (17,2)
************************************************************************
ps_product:				quantity, minimal_quantity,out_of_stock
ps_order_return_detail:			product_quantity
ps_pack:				quantity
ps_product_attribute:			quantity, minimal_quantity
ps_product_sale:			quantity
ps_stock:				physical_quantity, usable_quantity
ps_cart_rule:				quantity, quantity_per_user
ps_customization:			quantity, quantity_refunded, quantity_returned
ps_order_detail:			product_quantity, product_quantity_in_stock, product_quantity_refunded, product_quantity_return,product_quantity_reinjected
ps_specific_price_rule:			from_quantity
ps_order_slip_detail:			product_quantity
ps_supply_order_detail:			quantity_recieved, quantity_expected
ps_stock_available:			quantity 
ps_cart_product:			quantity 
ps_stock_mvt:				physical_quantity
ps_cart_rule_product_rule_group:	quantity
ps_product_shop:			minimal_quantity
ps_supply_order_receipt_history:	quantity
ps_product_attribute_shop:		minimal_quantity
************************************************************************
classes\Cart.php
classes\order\OrderDetail.php
classes\controller\FrontController.php
modules\blockcart\blockcart.php
themes\default-bootstrap\product.tpl
themes\default-bootstrap\order-detail.tpl
themes\default-bootstrap\js\product.js
themes\default-bootstrap\js\cart-summary.js
themes\default-bootstrap\modules\blockcart\blockcart-json.tpl
themes\default-bootstrap\modules\blockcart\blockcart.tpl
admin\themes\default\template\controllers\orders\_product_line.tpl
************************************************************************
classes\Cart.php
617	$row['stock_quantity'] = (float)$row['quantity'];
619	$row['quantity'] = (float)$row['cart_quantity'];
701	$row['total'] = $row['price_with_reduction_without_tax'] * (float)$row['cart_quantity'];
702	$row['total_wt'] = $row['price_with_reduction'] * (float)$row['cart_quantity'];
705	$row['total'] = Tools::ps_round($row['price_with_reduction_without_tax'] * (float)$row['cart_quantity'], _PS_PRICE_COMPUTE_PRECISION_);
706	$row['total_wt'] = Tools::ps_round($row['price_with_reduction'] * (float)$row['cart_quantity'], _PS_PRICE_COMPUTE_PRECISION_);
711	$row['total'] = Tools::ps_round($row['price_with_reduction_without_tax'], _PS_PRICE_COMPUTE_PRECISION_) * (float)$row['cart_quantity'];
712	$row['total_wt'] = Tools::ps_round($row['price_with_reduction'], _PS_PRICE_COMPUTE_PRECISION_) * (float)$row['cart_quantity'];
820	self::$_nbProducts[$id] = (float)Db::getInstance()->getValue('
928	$quantity = (float)$quantity;
942	$minimal_quantity = (float)Attribute::getAttributeMinimalQty($id_product_attribute);
944	$minimal_quantity = (float)$product->minimal_quantity;
971	if ((float)$quantity <= 0) {
988	$product_qty = (float)$result2['quantity'];
*993	$new_qty = (float)$result['quantity'] + (float)$quantity;
*994	$qty = '+ '.(float)$quantity;
996	if (!Product::isAvailableWhenOutOfStock((float)$result2['out_of_stock'])) {
1002	$qty = '- '.(float)$quantity;
1003	$new_qty = (float)$result['quantity'] - (float)$quantity;
1041	if (!Product::isAvailableWhenOutOfStock((float)$result2['out_of_stock'])) {
1042	if ((float)$quantity > $result2['quantity']) {
1047	if ((float)$quantity < $minimal_quantity) {
1057	'quantity' =>                (float)$quantity,
1078	return $this->_updateCustomizationQuantity((float)$quantity, (int)$id_customization, (int)$id_product, (int)$id_product_attribute, (int)$id_address_delivery, $operator);
1096	SET `quantity` = '.(float)$quantity.',
1106	if (!empty($id_customization) && (float)$quantity < 1) {
1114	if ($operator == 'down' && (float)$result['quantity'] - (float)$quantity < 1) {
1121	`quantity` = `quantity` '.($operator == 'up' ? '+ ' : '- ').(float)$quantity.',
1181	VALUES ('.(int)$this->id.', '.(int)$id_product.', '.(int)$id_product_attribute.', '.(float)$quantity.')'
1261	$product_total_quantity = (float)Db::getInstance()->getValue(
1268	$customization_quantity = (float)Db::getInstance()->getValue('
1298	if (Db::getInstance()->NumRows() && (float)$result['quantity']) {
1301	SET `quantity` = '.(float)$result['quantity'].'
1363	SET `quantity` = `quantity` - '.(float)$customization['quantity'].'
1572	$products_total[$id_tax_rules_group.'_'.$id_address] += $price * (float)$product['cart_quantity'];
1583	$products_total[$id_tax_rules_group] += Tools::ps_round($product_price, $compute_precision) * (float)$product['cart_quantity'];
3579	VALUES('.(int)$cart->id.', '.(int)$val['id_product_attribute'].', '.(int)$val['id_product'].', '.(int)$id_address_delivery.', '.(float)$val['quantity'].', 0, 0, 1)'
3630	(float)$value['quantity'].', NOW(), '.(int)Context::getContext()->shop->id.'),';
3686	`quantity` = `quantity` + '.(float)$result.'
3736	'.(float)$quantity.',
3754	SET `quantity` = `quantity` - '.(float)$quantity.'
3783	'.(float)$quantity.',
4007	if (((float)$product['quantity_available'] - (float)$product['cart_quantity']) < 0
4012	if ((float)$product['quantity_available'] <= 0
4016	if ((float)$product['quantity_available'] > 0
************************************************************************
classes\controller\FrontController.php
452              'cart_qties'          => (float)$cart->nbProducts(),
************************************************************************
modules\blockcart\blockcart.php
65	$nbTotalProducts += (float)$product['cart_quantity'];
145	'nb_total_products' => (float)($nbTotalProducts),
************************************************************************
themes\default-bootstrap\order-detail.tpl
208	<input class="order_qte_input form-control grey"  name="order_qte_input[{$smarty.foreach.products.index}]" type="text" size="2" value="{$product.customizationQuantityTotal|floatval}" />
213	<label for="cb_{$product.id_order_detail|intval}"><span class="order_qte_span editable">{$product.customizationQuantityTotal|floatval}</span></label></td>
269	<input class="order_qte_input form-control grey" name="customization_qty_input[{$customizationId|intval}]" type="text" size="2" value="{$customization.quantity|floatval}" />
274	<label for="cb_{$product.id_order_detail|intval}"><span class="order_qte_span editable">{$customization.quantity|floatval}</span></label>
307	<input class="order_qte_input form-control grey" name="order_qte_input[{$product.id_order_detail|intval}]" type="text" size="2" value="{$productQuantity|floatval}" />
312	<label for="cb_{$product.id_order_detail|intval}"><span class="order_qte_span editable">{$productQuantity|floatval}</span></label></td>
************************************************************************
themes\default-bootstrap\modules\blockcart\blockcart.tpl
239	{l s='There are [1]%d[/1] items in your cart.' mod='blockcart' sprintf=[$cart_qties] tags=['<span class="ajax_cart_quantity">']}
************************************************************************
themes\default-bootstrap\modules\blockcart\blockcart-json.tpl
34	"quantity": {$product.cart_quantity|floatval},
************************************************************************
themes\default-bootstrap\js\cart-summary.js
nbrProducts += parseFloat(product_list[i].quantity);
************************************************************************
Back Office
classes\order\OrderDetail.php
175	'product_quantity' =>            array('type' => self::TYPE_FLOAT, 'validate' => 'isFloat', 'required' => true),
176	'product_quantity_in_stock' =>    array('type' => self::TYPE_FLOAT, 'validate' => 'isFloat'),
177	'product_quantity_return' =>    array('type' => self::TYPE_FLOAT, 'validate' => 'isFloat'),
178	'product_quantity_refunded' =>    array('type' => self::TYPE_FLOAT, 'validate' => 'isFloat'),
179	'product_quantity_reinjected' =>array('type' => self::TYPE_FLOAT, 'validate' => 'isFloat'),
198	'discount_quantity_applied' =>    array('type' => self::TYPE_FLOAT, 'validate' => 'isFloat'),
622	$this->product_quantity = (float)$product['cart_quantity'];
630	$product_quantity = (float)Product::getQuantity($this->product_id, $this->product_attribute_id);
631	$this->product_quantity_in_stock = ($product_quantity - (float)$product['cart_quantity'] < 0) ?
632	$product_quantity : (float)$product['cart_quantity'];
************************************************************************
Back Office
admin\themes\default\template\controllers\orders\_product_line.tpl
79	<span class="product_quantity_show{if (float)$product['product_quantity'] > 1} badge{/if}">{$product['product_quantity']}</span>
************************************************************************
************************************************************************
        Edit product.tpl and product.js Depend on What You Want
************************************************************************
************************************************************************
key up and down (+,-)
themes\default-bootstrap\product.tpl
						<!-- quantity wanted -->
						{if !$PS_CATALOG_MODE}

						{assign cat16 [['id_category' => 16]]}
						{assign cat17 [['id_category' => 17]]}
						
						{if Product::idIsOnCategoryId($smarty.get.id_product, $cat16)}
						<p id="quantity_wanted_p"{if (!$allow_oosp && $product->quantity <= 0) || !$product->available_for_order || $PS_CATALOG_MODE} style="display: none;"{/if}>
						<label for="quantity_wanted">{l s='Quantity'}</label>
						<input type="text" min="1" name="qty" id="quantity_wanted" class="text" disabled="disabled" value="{if isset($quantityBackup)}{$quantityBackup|intval}{else}{if $product->minimal_quantity > 1}{$product->minimal_quantity}{else}1{/if}{/if}" />
                        <a href="#" data-field-qty="qty" class="btn btn-default button-minus product_quantity_down_1">
                        	<span><i class="icon-minus"></i></span>
                        </a>
                        <a href="#" data-field-qty="qty" class="btn btn-default button-minus product_quantity_up_1">
                         	<span><i class="icon-plus"></i></span>
							</a>
						</p>
						
						{elseif Product::idIsOnCategoryId($smarty.get.id_product, $cat17)}
						<p id="quantity_wanted_p"{if (!$allow_oosp && $product->quantity <= 0) || !$product->available_for_order || $PS_CATALOG_MODE} style="display: none;"{/if}>
						<label for="quantity_wanted">{l s='Quantity'}</label>
						<input type="text" min="2" name="qty" id="quantity_wanted" class="text" disabled="disabled" value="{if isset($quantityBackup)}{$quantityBackup|intval}{else}{if $product->minimal_quantity > 1}{$product->minimal_quantity}{else}1{/if}{/if}"  />
                        <a href="#" data-field-qty="qty" class="btn btn-default button-minus product_quantity_down_2">
                        	<span><i class="icon-minus"></i></span>
                        </a>
                        <a href="#" data-field-qty="qty" class="btn btn-default button-minus product_quantity_up_2">
                         	<span><i class="icon-plus"></i></span>
							</a>
						</p>
						
						{else}
						<p id="quantity_wanted_p"{if (!$allow_oosp && $product->quantity <= 0) || !$product->available_for_order || $PS_CATALOG_MODE} style="display: none;"{/if}>
							<label for="quantity_wanted">{l s='Quantity'}</label>
							<input type="number" min="1"  name="qty" id="quantity_wanted" disabled="disabled" class="text" value="{if isset($quantityBackup)}{$quantityBackup|intval}{else}{if $product->minimal_quantity > 1}{$product->minimal_quantity}{else}1{/if}{/if}" />
							<a href="#" data-field-qty="qty" class="btn btn-default button-minus product_quantity_down_3">
								<span><i class="icon-minus"></i></span>
							</a>
							<a href="#" data-field-qty="qty" class="btn btn-default button-plus product_quantity_up_3">
								<span><i class="icon-plus"></i></span>
							</a>
							<span class="clearfix"></span>
						</p>	

						{/if}
						{/if}
************************************************************************
key up and down (+,-)
themes\default-bootstrap\js\product.js
// The button to increment the product value
$(document).on('click', '.product_quantity_up_1', function(e){
        e.preventDefault();
        fieldName = $(this).data('field-qty');
        var currentVal = parseInt($('input[name='+fieldName+']').val());
        if (!allowBuyWhenOutOfStock && quantityAvailable > 0)
                quantityAvailableT = quantityAvailable;
        else
                quantityAvailableT = 100000000;
        if (!isNaN(currentVal) && currentVal < quantityAvailableT)
                $('input[name='+fieldName+']').val(currentVal + 1).trigger('keyup');
        else
                $('input[name='+fieldName+']').val(quantityAvailableT);

        $('#quantity_wanted').change();
});
 // The button to decrement the product value
$(document).on('click', '.product_quantity_down_1', function(e){
        e.preventDefault();
        fieldName = $(this).data('field-qty');
        var currentVal = parseInt($('input[name='+fieldName+']').val());
        if (!isNaN(currentVal) && currentVal > 1 && currentVal > 1)
                $('input[name='+fieldName+']').val(currentVal - 1).trigger('keyup');
        else
                $('input[name='+fieldName+']').val(1);

        $('#quantity_wanted').change();    
});

// The button to increment the product value
$(document).on('click', '.product_quantity_up_2', function(e){
        e.preventDefault();
        fieldName = $(this).data('field-qty');
        var currentVal = parseInt($('input[name='+fieldName+']').val());
        if (!allowBuyWhenOutOfStock && quantityAvailable > 0)
                quantityAvailableT = quantityAvailable;
        else
                quantityAvailableT = 100000000;
        if (!isNaN(currentVal) && currentVal < quantityAvailableT)
                $('input[name='+fieldName+']').val(currentVal + 2).trigger('keyup');
        else
                $('input[name='+fieldName+']').val(quantityAvailableT);

        $('#quantity_wanted').change();
});
 // The button to decrement the product value
$(document).on('click', '.product_quantity_down_2', function(e){
        e.preventDefault();
        fieldName = $(this).data('field-qty');
        var currentVal = parseInt($('input[name='+fieldName+']').val());
        if (!isNaN(currentVal) && currentVal > 1 && currentVal > 2)
                $('input[name='+fieldName+']').val(currentVal - 2).trigger('keyup');
        else
                $('input[name='+fieldName+']').val(2);

        $('#quantity_wanted').change();    
});

// The button to increment the product value
$(document).on('click', '.product_quantity_up_3', function(e){
        e.preventDefault();
        fieldName = $(this).data('field-qty');
        var currentVal = parseFloat($('input[name='+fieldName+']').val());
        if (!allowBuyWhenOutOfStock && quantityAvailable > 0)
                quantityAvailableT = quantityAvailable;
        else
                quantityAvailableT = 100000000;
        if (!isNaN(currentVal) && currentVal < quantityAvailableT)
                $('input[name='+fieldName+']').val(currentVal + 0.5).trigger('keyup');
        else
                $('input[name='+fieldName+']').val(quantityAvailableT);

        $('#quantity_wanted').change();
});
 // The button to decrement the product value
$(document).on('click', '.product_quantity_down_3', function(e){
        e.preventDefault();
        fieldName = $(this).data('field-qty');
        var currentVal = parseFloat($('input[name='+fieldName+']').val());
        if (!isNaN(currentVal) && currentVal > 1 && currentVal > 0.5)
                $('input[name='+fieldName+']').val(currentVal - 0.5).trigger('keyup');
        else
                $('input[name='+fieldName+']').val(0.5);

        $('#quantity_wanted').change();    
});