How can i separate the integer part of a number from its decimal part ?

[archnim]

Hello world. This is my code.
    
    
    import math
        
        var
            num = 786.654
            intPart = floor num
            decPart = num - intPart
        
        echo decPart #got 0.6539999999999964 instead of 0.654
    
    
    Run

I get worse results when I add digits to the decimal part. Please, is there any 
reliable way to extract the decimal part of a number ? I need it for a 
multiprecision library.