Return a copy of src.
Long integer representation. The absolute value of a number is equal to SUM(for i=0 through abs(ob_size)-1) ob_digiti * 2**(SHIFT*i) Negative numbers are represented with ob_size < 0; zero is represented by ob_size == 0. In a normalized number, ob_digit[abs(ob_size)-1] (the most significant digit) is never zero. Also, in all cases, for all valid i, 0 <= ob_digiti <= MASK. The allocation function takes care of allocating extra memory so that ob_digit ... ob_digit[abs(ob_size)-1] are actually available.