How do I improve the speed of Galois fields?

have a code about "Random linear network coding Encoding, decoding" system and I need a high speed

I have a problem with the Galois fields which is causing the code to slow down

this line of the equation

  g_loc=gf(randi(2*q-1,[l,x]),q);

How do I improve the speed of Galois fields?How do I improve Galois fields?