// My custom X type detection
int buf0,buf1,mystart;
int type,state,jstart,jend;
enum {DEFAULT=1,YOURTYPE}; //internal enum
enum {NONE=0,START,INFO,END,RESET=0xfffffffe,REQUEST=0xffffffff}; //external enum
// function will report its state 
// or if i=-1 then state results otherwise i is pos
// c4 is last 4 bytes
void reset(){
    state=NONE,type=DEFAULT,jstart=jend=buf0=buf1=mystart=0;
}
int detect(int c4,int i) {
    // If detect state parameters recuested
    if (i==REQUEST){
        if (state==NONE)  return 0xffffffff;  // No state
        if (state==START) return jstart;      // Report data start
        if (state==END)   return jend;        // Report data end
        if (state==INFO)  return 0xffffffff;  // Report info if any
    }
    if (i==RESET){
        reset();
        return 0xffffffff;
    }
    buf1=(buf1<<8)|(buf0>>24);
    buf0=c4;
    // Detect header - is first four bytes 0xFFFFFFFF
    if (buf1==0xFFFFFFFF && mystart==0){
        mystart=i;
    }
    // Found possible start, report
    if (type==DEFAULT && mystart){
        type=YOURTYPE;
        state=START; 
        jstart=mystart-4;
        return state;
    }
    // Found end, report if our type
    if (i-mystart>0x100){
        if (type==YOURTYPE){
            state=END;
            type=DEFAULT;
            jend=i;
            return state;
      }
      state=NONE;
      type=DEFAULT;
      mystart=0;
    }
    return NONE;
}

int main() {
    reset();
}

// update is called by vm for every input bit
// y    - last bit
// c0   - last 0-7 bits of the partial byte with a leading 1 bit (1-255)
// c4   - last 4,4 whole bytes, packed.  Last byte is bits 0-7.
// bpos - bits in c0 (0 to 7)
// pr   - last prediction
int t[5]={};
enum {SMC=1,APM1,DS,AVG,SCM,RCM,CM,MX,ST,MM,DHS};

int update(int y,int c0,int bpos,int c4,int pr){
    int i;
    if (bpos==0) {
        for (i=4; i>0; --i) t[i]=h2(t[i-1],c4&0xff);
    }
    for (i=1;i<5;  i) 
    vmx(DS,0,(c0)|(t[i]<<8));
    vmx(APM1,0,c0);
    return 0;
}

// called at the start of every new data type
// a - info
// b - reserved (not used and set to 0)
void block(int a,int b) {}

// called once at the start of compression
int main(){ 
    vms(0,1,1,3,0,0,0,0,0,0,0);
    vmi(DS,0,18,1023,4);        // pr[0]..pr[3]
    vmi(AVG,0,0,0,1);           // pr[4]=avg(pr[0],pr[1])
    vmi(AVG,1,0,2,3);           // pr[5]=avg(pr[2],pr[3])
    vmi(AVG,2,0,4,5);           // pr[6]=avg(pr[4],pr[5])
    vmi(APM1,0,256,7,6);        // pr[7]=apm(pr[6]) rate 7 -> pr[7] is final prediction
}