# Issue

This Content is from Stack Overflow. Question asked by piggogo

How does gmp recognize a signed integer? When I use the gmp library, I can safely put two large positive integers or unsigned integers into the mpz_ tdiv_q () function performs division calculation, but I’m curious when I convert two 8-byte memory cells to mpz_t by using the function to convert a large negative integers, how does gmp recognize it as a negative number? Can i safely put it into the mpz_tdiv_q for division calculation?The large integer inside mpz_t stores numbers according to the complete storage unit. For example, 120 bits will occupy two consecutive 64 bit storage units. If it is a negative number at this time, do I need to expand its bit size and then use mpz_ tdiv_ q () for division calculation?

``````    uint64_t ext_lhs;
uint64_t ext_rhs;
mpn_copyi(ext_lhs, lhs, 2);
mpn_copyi(ext_rhs, rhs, 2);
//sign bit expansion for the highest bit,Is it unnecessary?
if(overwidth){
svs_sext_to_bv64x_from_bv64x(ext_lhs, 2, width, lhs, 2 - 1, overwidth);
svs_sext_to_bv64x_from_bv64x(ext_rhs, 2, width, rhs, 2 - 1, overwidth);
}
mpz_t res, left, right;
mpz_init(res);
mpz_tdiv_q(res, mpz_roinit_n(left, ext_lhs, 2), mpz_roinit_n(right, ext_rhs, 2));
``````

# Solution

The `size` argument of `mpz_roinit_n` has 2 purposes. Its absolute value encodes the number of limbs, while its sign encodes the sign of the resulting number. The array of limbs always corresponds to a positive number there is no sign bit or 1/2-s complement.

``` This Question was asked in  StackOverflow by  piggogo and Answered by Marc Glisse It is licensed under the terms of
CC BY-SA 2.5. - CC BY-SA 3.0. - CC BY-SA 4.0.```