Description:
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Attempting to subtract one floating point number from another returns the incorrect result. Float 1 is assigned in the code, float 2 is retrieved from a mysql DB field, which is of type DECIMAL(5,4).

When subtracting $float1 from $float2 the result is:
-7.105427357601E-015  

Reproduce code:
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//Field discount2 is defined as type DECIMAL(5.4). Original value in database is 0.56, use PHP to multiply by 100 to get a whole number (56).

$result = mysql_query("SELECT `discount2` 
FROM `product_discounts` 
WHERE `product_id` = 'prod1'"); 

$discount2 = mysql_result($result)*100; 
$discount1 = 56; 

echo $discount1; //56 
echo $discount2; //56 

if ($discount2 != $discount1)
  echo "Discount1 not equal to Discount2"; //Y
if (bccomp($discount1,$discount2) == 0)
  echo "Discount1 equal to Discount2"; //Y


echo ($discount1 + $discount2); //112 
echo ($discount1 - $discount2); //-7.105427357601E-015  


Expected result:
----------------
When subtracting $discount1 from $discount2 I expected to get 0. When adding the two I get the expected 112.

Actual result:
--------------
When subtracting $discount1 from $discount2 I get:
-7.105427357601E-015