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Annotation of researchv9/cmd/compress/btoa.c, revision 1.1

1.1     ! root        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: }

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