excerpt-malloc.c

    if ((unsigned long)(nb) <= (unsigned long)(get_max_fast ()))
        {
            idx = fastbin_index(nb);
            mfastbinptr* fb = &fastbin (av, idx);
            mchunkptr pp = *fb;
            do
                {
                    victim = pp;
                    if (victim == NULL)
                        break;
                }
            while ( (pp = catomic_compare_and_exchange_val_acq (fb, victim->fd, victim)) != victim);
            
			if (victim != 0)
                {
                    check_remalloced_chunk(av, victim, nb);
                    void *p = chunk2mem(victim);
                    if ( perturb_byte) alloc_perturb (p, bytes);
                    return p;
                }
        }