implement Stein's algorithm for gcd
implement Stein's algorithm for gcd

rust-num/num,rust-num/num-traits,koverstreet/num,anchovieshat/num,anchovieshat/num,rust-lang/num,Emerentius/num,rust-num/num-integer,achanda/num,achanda/num,jbcrail/num,rust-lang/num,vks/num,rust-num/num-bigint,DonSheddow/num,jbcrail/num,vks/num,rust-num/num,rust-num/num-bigint,rust-num/num-integer,koverstreet/num,rust-num/num-traits,DonSheddow/num