Fast forward conversion algorithm

I am trying to find the fastest algorithm to go to edge conversion. The one that was used, for example, in combination with the conversion of burrow wheels.

The best I managed to do is about 15 MB / s on the Core i3 2.1 GHz. But I am sure that this is not optimal. Here are my best efforts. Is there anything faster?

class mtf256_x {                                                                            
        typedef unsigned char u8;
        typedef unsigned long long L;
        public:
        L enc[37];
        u8 dec[256];
        mtf256_x() {
                unsigned i;
                for (i=0;i<37;i++) {
                        enc[i]=0;
                }
                for (i=0;i<256;i++) {
                        dec[i]=i;
                        set(i,i);
                }
        }
        u8 decode(u8 in) {
                u8 r = dec[in];                                                             
                if (in) {                                                                   
                        memmove(dec+1,dec,in);                                              
                        dec[0]=r;                                                           
                }                                                                           
                return r;                                                                   
        }                                                                                   
        u8 set(unsigned x, u8 y) {                                                          
                unsigned xl = (x%7)*9;                                                      
                unsigned xh = (x/7);                                                        
                enc[xh] &= ~(0x1FFLLU<<xl);                                                 
                enc[xh] |= ((L)y)<<xl;                                                      
        }                                                                                   
        u8 get(unsigned x) {                                                                
                return enc[x/7] >> (x%7)*9;                                                 
        }                                                                                   
        u8 encode(u8 in) {                                                                  
                u8 r;
                unsigned i;
                r = get(in);
                L m2 = 0x0040201008040201LLU; // 0x01 for each 9 bit int                    
                L m1 = 0x3FDFEFF7FBFDFEFFLLU; // 0xff for each 9 bit int                    
                L Q = (0x100+r)*m2;                                                         
                L a,b,c,d;                                                                  
                L * l= enc;                                                                 
                for (i=0;i<37;i++) {                                                        
                        a=l[i];
                        a+= ((Q-a)>>8)&m2;  // conditional add 1
                        a&=m1;
                        l[i]=a;
                }
                set(in,0);
                return r;
        }
};