http://benji3up2kxewkqfcq7buxk2xd6zwy3zggnurkrm3l4cvwy2iipvyyad.onion/mirrors/gmpdoc/Integer-Special-Functions.html
The array should contain abs( s ) valid limbs,
representing the new absolute value for x , and the sign of x is
taken from the sign of s . This function never reallocates x , so
the limb pointer remains valid. void foo (mpz_t x)
{
mp_size_t n, i;
mp_limb_t *xp;
n = mpz_size (x);
xp = mpz_limbs_modify (x, 2*n);
for (i = 0; i < n; i++)
xp[n+i] = xp[n-1-i];
mpz_limbs_finish...