Multiply two Big Numbers.

Prototype
   int BigNum.mul( bnum1 , bnum2 , bnum3 )

Parameters
   bnum1 and bnum2
      Numbers to be multiplied.
   bnum3
      Returns the multiplication of bnum1 and bnum2.

Remarks
   bnum1, bnum2, bnum3 must be created before function call

Example
   
require( "BigNum.lua" )
		   		   
a = BigNum.new( "639" )
b = BigNum.new( "563" )
result = BigNum.new( )
BigNum.mul( a , b , result )
print( a .. " * " .. b .. " = " .. result )

a = BigNum.new( "-543" )
b = BigNum.new( "1256" )
BigNum.mul( a , b , result )
print( a .. " * " .. b .. " = " .. result )

--Try to add non valid parameters
ret = BigNum.mul( a , d , result )
print( ret ) ;
   

Output
   
639 * 563 = 359757
-543 * 1256 = 682008
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