sys/src/cmd/crc32.c

   1 #include <u.h>
   2 #include <libc.h>
   3 #include <libsec.h>
   4
   5 u32int table[256];
   6 u32int xor = -1, init, poly = 0xedb88320;
   7 char *error;
   8
   9 static void
  10 dotable(void)
  11 {
  12         u32int c;
  13         int n, k;
  14
  15         for(n = 0; n < 256; n++){
  16                 c = n;
  17                 for(k = 0; k < 8; k++)
  18                         if((c & 1) != 0)
  19                                 c = poly ^ c >> 1;
  20                         else
  21                                 c >>= 1;
  22                 table[n] = c;
  23         }
  24 }
  25
  26 static u32int
  27 calc(u32int init, uchar *buf, ulong len)
  28 {
  29         u32int c;
  30
  31         c = init;
  32         while(len-- != 0)
  33                 c = table[(*buf++ ^ c) & 0xff] ^ c >> 8;
  34         return c;
  35 }
  36
  37 static void
  38 sum(int fd, char *name)
  39 {
  40         int n;
  41         uchar buf[8192];
  42         u32int crc;
  43
  44         crc = init ^ xor;
  45         while((n = read(fd, buf, sizeof buf)) > 0)
  46                 crc = calc(crc, buf, n);
  47         if(n < 0){
  48                 fprint(2, "reading %s: %r\n", name ? name : "stdin");
  49                 error = "read";
  50                 return;
  51         }
  52         crc ^= xor;
  53         if(name == nil)
  54                 print("%ux\n", crc);
  55         else
  56                 print("%ux\t%s\n", crc, name);
  57 }
  58
  59 void
  60 usage(void)
  61 {
  62         fprint(2, "usage: %s [-x xorval] [-i initial] [-p poly] [file...]\n", argv0);
  63         exits("usage");
  64 }
  65
  66 void
  67 main(int argc, char *argv[])
  68 {
  69         int i, fd;
  70
  71         ARGBEGIN{
  72         case 'x':
  73                 xor = strtol(EARGF(usage()), 0, 0);
  74                 break;
  75         case 'i':
  76                 init = strtol(EARGF(usage()), 0, 0);
  77                 break;
  78         case 'p':
  79                 poly = strtol(EARGF(usage()), 0, 0);
  80                 break;
  81         default:
  82                 usage();
  83         }ARGEND
  84
  85         dotable();
  86         if(argc == 0)
  87                 sum(0, nil);
  88         else for(i = 0; i < argc; i++){
  89                 fd = open(argv[i], OREAD);
  90                 if(fd < 0){
  91                         fprint(2, "crc32: can't open %s: %r\n", argv[i]);
  92                         error = "open";
  93                         continue;
  94                 }
  95                 sum(fd, argv[i]);
  96                 close(fd);
  97         }
  98         exits(error);
  99 }