if (len) {                                                                                                                            
      sp = p + strlen(s1);                                                                                                                
      dp = sp + len;                                                                                                                      
      cnt = strlen(sp) + 1;                                                                                                               
      memmove(p+strlen(s1)+len, p+strlen(s1), cnt);                                                                                       
    }                                                                                                                                     
    memcpy(p, s2, strlen(s2));                                                                                                            
    pos = p + strlen(s2);                                                                                                                 
    if (*pos == 0) {                                                                                                                      
        return s;                                                                                                                         
    }                                                                                                                                     
}                                                                                                                                       
}