X := [x1,x2,x3,x4,x5,x6,x7,x8];
E := rand(10):
C := rand(-99..99):
for i from 7 to 8 do
    printf("i=%d\n",i);
    n := 1000*2^i;
    f := 0;
    t := 0;
    while t<n do
       f := f + add( C()*mul(x^E(),x in X), j=1..n-t);
       t := nops(f);
    od;
    subs(FILE=f||n,proc() save f,FILE; end)();
od: