#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#include <strings.h>
#include <sys/file.h>

extern const char *__progname;

#define NEVER (-1)
#define MAYBE 0
#define ALWAYS 1
#define COMPAT 2

static int print_names = MAYBE;
static int bitswap = 0;

static unsigned long int tbl[256];
static unsigned long int mask;
static int width;
static int pwidth;
static unsigned long int init;

static const unsigned char swap8[256]
 = { 0, 128, 64, 192, 32, 160, 96, 224, 16, 144, 80, 208, 48, 176, 112,
     240, 8, 136, 72, 200, 40, 168, 104, 232, 24, 152, 88, 216, 56,
     184, 120, 248, 4, 132, 68, 196, 36, 164, 100, 228, 20, 148, 84,
     212, 52, 180, 116, 244, 12, 140, 76, 204, 44, 172, 108, 236, 28,
     156, 92, 220, 60, 188, 124, 252, 2, 130, 66, 194, 34, 162, 98,
     226, 18, 146, 82, 210, 50, 178, 114, 242, 10, 138, 74, 202, 42,
     170, 106, 234, 26, 154, 90, 218, 58, 186, 122, 250, 6, 134, 70,
     198, 38, 166, 102, 230, 22, 150, 86, 214, 54, 182, 118, 246, 14,
     142, 78, 206, 46, 174, 110, 238, 30, 158, 94, 222, 62, 190, 126,
     254, 1, 129, 65, 193, 33, 161, 97, 225, 17, 145, 81, 209, 49, 177,
     113, 241, 9, 137, 73, 201, 41, 169, 105, 233, 25, 153, 89, 217,
     57, 185, 121, 249, 5, 133, 69, 197, 37, 165, 101, 229, 21, 149,
     85, 213, 53, 181, 117, 245, 13, 141, 77, 205, 45, 173, 109, 237,
     29, 157, 93, 221, 61, 189, 125, 253, 3, 131, 67, 195, 35, 163, 99,
     227, 19, 147, 83, 211, 51, 179, 115, 243, 11, 139, 75, 203, 43,
     171, 107, 235, 27, 155, 91, 219, 59, 187, 123, 251, 7, 135, 71,
     199, 39, 167, 103, 231, 23, 151, 87, 215, 55, 183, 119, 247, 15,
     143, 79, 207, 47, 175, 111, 239, 31, 159, 95, 223, 63, 191, 127,
     255 };

static unsigned long int swap_width(unsigned long int v, int w)
{
 unsigned long int s;

 s = 0;
 for (;w>0;w--)
  { s = (s << 1) | (v & 1);
    v >>= 1;
  }
 return(s);
}

static void get_polynomial(const char *str)
{
 char *ep;
 unsigned long int poly;
 unsigned long int v;
 int i;
 int j;

 poly = strtoul(str,&ep,16);
 if ((str == ep) || *ep)
  { fprintf(stderr,"%s: invalid polynomial `%s'\n",__progname,str);
    exit(1);
  }
 mask = poly;
 for (i=16;i>=1;i>>=1) mask |= mask >> i;
 for (v=mask,width=0;v;width++,v>>=1) ;
 pwidth = (width + 3) >> 2;
 for (i=0;i<256;i++)
  { v = i;
    for (j=0;j<8;j++) if (v & 1) v = (v >> 1) ^ poly; else v >>= 1;
    tbl[i] = v;
  }
}

static void get_initial(const char *str)
{
 char *ep;

 init = strtoul(str,&ep,16);
 if ((str == ep) || *ep)
  { fprintf(stderr,"%s: invalid initial value `%s'\n",__progname,str);
    exit(1);
  }
 if (init & ~mask)
  { fprintf(stderr,"%s: initial value is too wide for polynomial\n",__progname);
    exit(1);
  }
}

static void process_file(int fd, void (*pfn)(void *, unsigned long int), void *parg, const char *fn)
{
 int n;
 unsigned long int v;
 int i;
 static unsigned char buf[65536];

 v = init;
 while (1)
  { n = read(fd,&buf[0],sizeof(buf));
    if (n < 0)
     { fprintf(stderr,"%s: read error on %s: %s\n",__progname,fn,strerror(errno));
       n = 0;
     }
    if (n == 0)
     { (*pfn)(parg,bitswap?swap_width(v,width):v);
       return;
     }
    for (i=0;i<n;i++) v = (v >> 8) ^ tbl[(v^(bitswap?swap8[buf[i]]:buf[i]))&0xff];
  }
}

static void scan_args(int *acp, char ***avp)
{
 int errs;
 int ac;
 char **av;
 int i;
 int j;

 errs = 0;
 ac = *acp;
 av = *avp;
 j = 1;
 for (i=1;i<ac;i++)
  { if (av[i][0] == '-')
     { if (!strcmp(av[i],"-h"))
	{ print_names = NEVER;
	}
       else if (!strcmp(av[i],"-H"))
	{ print_names = ALWAYS;
	}
       else if (!strcmp(av[i],"-c"))
	{ print_names = COMPAT;
	}
       else if (!strcmp(av[i],"-x"))
	{ bitswap = ! bitswap;
	}
       else
	{ fprintf(stderr,"%s: unknown flag %s\n",__progname,av[i]);
	  errs ++;
	}
     }
    else
     { if (j != i) av[j] = av[i];
       j ++;
     }
  }
 if (errs) exit(1);
 av[j] = 0;
 *acp = j;
}

static void print_sum_stdin(void *arg __attribute__((__unused__)), unsigned long int v)
{
 printf("%0*lx",pwidth,v);
 if (print_names == ALWAYS) printf(" stdin");
 printf("\n");
}

static void print_sum_file(void *arg, unsigned long int v)
{
 if (print_names == COMPAT) printf("CRC-%0*lx (%s) = ",pwidth,tbl[128],(const char *)arg);
 printf("%0*lx",pwidth,v);
 if (print_names == ALWAYS) printf(" %s",(const char *)arg);
 printf("\n");
}

int main(int, char **);
int main(int ac, char **av)
{
 scan_args(&ac,&av);
 if (ac < 3)
  { fprintf(stderr,"Usage: %s -[hHcx] polynomial initial [file [file ...]]\n",__progname);
    exit(1);
  }
 get_polynomial(av[1]);
 get_initial(av[2]);
 ac -= 2;
 av += 2;
 if (print_names == MAYBE) print_names = (ac < 3) ? NEVER : ALWAYS;
 if (ac == 1)
  { process_file(0,print_sum_stdin,0,"standard input");
    exit(0);
  }
 else
  { int i;
    int fd;
    int nerr;
    nerr = 0;
    for (i=1;i<ac;i++)
     { fd = open(av[i],O_RDONLY,0);
       if (fd < 0)
	{ fprintf(stderr,"%s: can't open %s: %s\n",__progname,av[i],strerror(errno));
	  nerr ++;
	}
       else
	{ process_file(fd,print_sum_file,av[i],av[i]);
	  close(fd);
	}
     }
    exit(nerr);
  }
}