/* COMBO a simple but very good combination generator. It combines, by addition mod 2^32, x(n)=x(n-1)*x(n-2) mod 2^32 and y(n)=30903*y(n-1) + carry mod 2^16 The period of the first is 3*2^29, on odd integers, and the period of the second, a multiply-with-carry generator, is 30903*2^15-1=1012629503, so the period of combo exceeds 2^60. This generator is simple to program in Fortran or C and quite fast. */ /* Simple combo, period > 2^60.5 x(n)=x(n-1)*x(n-2) mod 2^32 added to period of x(n)=x(n-1)*x(n-2) is 3*2^29 if both seeds are odd, and one is +or-3 mod 8. easy to ensure: replace seed x with 8*seed+3, and y with 2*seed+1 */ #define ulong unsigned long static ulong combo_x = 3; static ulong combo_y = 1; static ulong combo_z = 1; static ulong combo_v; void seed_rand_combo(ulong seed) { combo_x = seed * 8 + 3; combo_y = seed * 2 + 1; combo_z = seed | 1; } ulong rand_combo(void) { combo_v = combo_x * combo_y; combo_x = combo_y; combo_y = combo_v; combo_z = (combo_z & 65535) * 30903 + (combo_z >> 16); return combo_y + combo_z; }