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Function: mp_size_t mpn_gcdext (mp_limb_t * gp , mp_limb_t * sp , mp_size_t * sn , mp_limb_t * up , mp_size_t un , mp_limb_t * vp , mp_size_t vn ) ¶ Let U be defined by { up , un } and let V be
defined by { vp , vn }. Compute the greatest common divisor G of U and V .