base85.c

   1 #include "cache.h"
   2
   3 #undef DEBUG_85
   4
   5 #ifdef DEBUG_85
   6 #define say(a) fprintf(stderr, a)
   7 #define say1(a,b) fprintf(stderr, a, b)
   8 #define say2(a,b,c) fprintf(stderr, a, b, c)
   9 #else
  10 #define say(a) do {} while(0)
  11 #define say1(a,b) do {} while(0)
  12 #define say2(a,b,c) do {} while(0)
  13 #endif
  14
  15 static const char en85[] = {
  16         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
  17         'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
  18         'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
  19         'U', 'V', 'W', 'X', 'Y', 'Z',
  20         'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
  21         'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
  22         'u', 'v', 'w', 'x', 'y', 'z',
  23         '!', '#', '$', '%', '&', '(', ')', '*', '+', '-',
  24         ';', '<', '=', '>', '?', '@', '^', '_', '`', '{',
  25         '|', '}', '~'
  26 };
  27
  28 static char de85[256];
  29 static void prep_base85(void)
  30 {
  31         int i;
  32         if (de85['Z'])
  33                 return;
  34         for (i = 0; i < ARRAY_SIZE(en85); i++) {
  35                 int ch = en85[i];
  36                 de85[ch] = i + 1;
  37         }
  38 }
  39
  40 int decode_85(char *dst, char *buffer, int len)
  41 {
  42         prep_base85();
  43
  44         say2("decode 85 <%.*s>", len/4*5, buffer);
  45         while (len) {
  46                 unsigned acc = 0;
  47                 int cnt;
  48                 for (cnt = 0; cnt < 5; cnt++, buffer++) {
  49                         int ch = *((unsigned char *)buffer);
  50                         int de = de85[ch];
  51                         if (!de)
  52                                 return error("invalid base85 alphabet %c", ch);
  53                         de--;
  54                         if (cnt == 4) {
  55                                 /*
  56                                  * Detect overflow.  The largest
  57                                  * 5-letter possible is "|NsC0" to
  58                                  * encode 0xffffffff, and "|NsC" gives
  59                                  * 0x03030303 at this point (i.e.
  60                                  * 0xffffffff = 0x03030303 * 85).
  61                                  */
  62                                 if (0x03030303 < acc ||
  63                                     (0x03030303 == acc && de))
  64                                         error("invalid base85 sequence %.5s",
  65                                               buffer-3);
  66                         }
  67                         acc = acc * 85 + de;
  68                         say1(" <%08x>", acc);
  69                 }
  70                 say1(" %08x", acc);
  71                 for (cnt = 0; cnt < 4 && len; cnt++, len--) {
  72                         *dst++ = (acc >> 24) & 0xff;
  73                         acc = acc << 8;
  74                 }
  75         }
  76         say("\n");
  77
  78         return 0;
  79 }
  80
  81 void encode_85(char *buf, unsigned char *data, int bytes)
  82 {
  83         prep_base85();
  84
  85         say("encode 85");
  86         while (bytes) {
  87                 unsigned acc = 0;
  88                 int cnt;
  89                 for (cnt = 0; cnt < 4 && bytes; cnt++, bytes--) {
  90                         int ch = *data++;
  91                         acc |= ch << ((3-cnt)*8);
  92                 }
  93                 say1(" %08x", acc);
  94                 for (cnt = 0; cnt < 5; cnt++) {
  95                         int val = acc % 85;
  96                         acc /= 85;
  97                         buf[4-cnt] = en85[val];
  98                 }
  99                 buf += 5;
 100         }
 101         say("\n");
 102
 103         *buf = 0;
 104 }
 105
 106 #ifdef DEBUG_85
 107 int main(int ac, char **av)
 108 {
 109         char buf[1024];
 110
 111         if (!strcmp(av[1], "-e")) {
 112                 int len = strlen(av[2]);
 113                 encode_85(buf, av[2], len);
 114                 if (len <= 26) len = len + 'A' - 1;
 115                 else len = len + 'a' - 26 + 1;
 116                 printf("encoded: %c%s\n", len, buf);
 117                 return 0;
 118         }
 119         if (!strcmp(av[1], "-d")) {
 120                 int len = *av[2];
 121                 if ('A' <= len && len <= 'Z') len = len - 'A' + 1;
 122                 else len = len - 'a' + 26 + 1;
 123                 decode_85(buf, av[2]+1, len);
 124                 printf("decoded: %.*s\n", len, buf);
 125                 return 0;
 126         }
 127         if (!strcmp(av[1], "-t")) {
 128                 char t[4] = { -1,-1,-1,-1 };
 129                 encode_85(buf, t, 4);
 130                 printf("encoded: D%s\n", buf);
 131                 return 0;
 132         }
 133 }
 134 #endif