Based on the theoretical analysis of the conditions of the fast or slow light without distortion for arbitrary signal, a universal formula of an optimized Brillouin comb gain is obtained in accordance with the spectrum characteristics of the periodic signal. According to the amount of delay or advancement required, each Brillouin gain intensity and frequency detuning between Brillouin gain peak and the corresponding harmonic frequency of periodic signal can be found conveniently using this universal formula, then the whole Brillouin comb gain is identified. Numerical calculation for sinusoidal signal, Gaussian periodic signal and square periodic signal is performed. The results show that zero-broadening slow and fast light is achieved using this optimized Brillouin comb gain for the three types of periodic signals, and the validity of the universal formula is proved. Moreover, the magnitude of the delay or advancement can be tuned continuously by adjusting the Brillouin gain intensity and frequency detuning.