diplodocus.org Git - nmh/blob - docs/historical/mh-6.8.5/miscellany/compress-4.0/btoa.c

   1 /* btoa: version 4.0
   2  * stream filter to change 8 bit bytes into printable ascii
   3  * computes the number of bytes, and three kinds of simple checksums
   4  * incoming bytes are collected into 32-bit words, then printed in base 85
   5  *  exp(85,5) > exp(2,32)
   6  * the ASCII characters used are between '!' and 'u'
   7  * 'z' encodes 32-bit zero; 'x' is used to mark the end of encoded data.
   8  *
   9  *  Paul Rutter         Joe Orost
  10  *  philabs!per         petsd!joe
  11  *
  12  *  WARNING: this version is not compatible with the original as sent out
  13  *  on the net.  The original encoded from ' ' to 't'; which cause problems
  14  *  with some mailers (stripping off trailing blanks).
  15  */
  16
  17 #include <stdio.h>
  18
  19 #define reg register
  20
  21 #define MAXPERLINE 78
  22
  23 long int Ceor = 0;
  24 long int Csum = 0;
  25 long int Crot = 0;
  26
  27 long int ccount = 0;
  28 long int bcount = 0;
  29 long int word;
  30
  31 #define EN(c)   (int) ((c) + '!')
  32
  33 encode(c)
  34   reg c;
  35 {
  36   Ceor ^= c;
  37   Csum += c;
  38   Csum += 1;
  39   if ((Crot & 0x80000000)) {
  40     Crot <<= 1;
  41     Crot += 1;
  42   } else {
  43     Crot <<= 1;
  44   }
  45   Crot += c;
  46
  47   word <<= 8;
  48   word |= c;
  49   if (bcount == 3) {
  50     wordout(word);
  51     bcount = 0;
  52   } else {
  53     bcount += 1;
  54   }
  55 }
  56
  57 wordout(word)
  58   reg long int word;
  59 {
  60   if (word == 0) {
  61     charout('z');
  62   } else {
  63     reg int tmp = 0;
  64
  65     if(word < 0) {      /* Because some don't support unsigned long */
  66       tmp = 32;
  67       word = word - (long)(85 * 85 * 85 * 85 * 32);
  68     }
  69     if(word < 0) {
  70       tmp = 64;
  71       word = word - (long)(85 * 85 * 85 * 85 * 32);
  72     }
  73     charout(EN((word / (long)(85 * 85 * 85 * 85)) + tmp));
  74     word %= (long)(85 * 85 * 85 * 85);
  75     charout(EN(word / (85 * 85 * 85)));
  76     word %= (85 * 85 * 85);
  77     charout(EN(word / (85 * 85)));
  78     word %= (85 * 85);
  79     charout(EN(word / 85));
  80     word %= 85;
  81     charout(EN(word));
  82   }
  83 }
  84
  85 charout(c) {
  86   putchar(c);
  87   ccount += 1;
  88   if (ccount == MAXPERLINE) {
  89     putchar('\n');
  90     ccount = 0;
  91   }
  92 }
  93
  94 main(argc,argv)
  95   char **argv;
  96 {
  97   reg c;
  98   reg long int n;
  99
 100   if (argc != 1) {
 101     fprintf(stderr,"bad args to %s\n", argv[0]);
 102     exit(2);
 103   }
 104   printf("xbtoa Begin\n");
 105   n = 0;
 106   while ((c = getchar()) != EOF) {
 107     encode(c);
 108     n += 1;
 109   }
 110   while (bcount != 0) {
 111     encode(0);
 112   }
 113   /* n is written twice as crude cross check*/
 114   printf("\nxbtoa End N %ld %lx E %lx S %lx R %lx\n", n, n, Ceor, Csum, Crot);
 115   exit(0);
 116 }