base85.c

   1 #include "git-compat-util.h"
   2 #include "base85.h"
   3
   4 #undef DEBUG_85
   5
   6 #ifdef DEBUG_85
   7 #define say(a) fprintf(stderr, a)
   8 #define say1(a,b) fprintf(stderr, a, b)
   9 #define say2(a,b,c) fprintf(stderr, a, b, c)
  10 #else
  11 #define say(a) do { /* nothing */ } while (0)
  12 #define say1(a,b) do { /* nothing */ } while (0)
  13 #define say2(a,b,c) do { /* nothing */ } while (0)
  14 #endif
  15
  16 static const char en85[] = {
  17         '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
  18         'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
  19         'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
  20         'U', 'V', 'W', 'X', 'Y', 'Z',
  21         'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
  22         'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
  23         'u', 'v', 'w', 'x', 'y', 'z',
  24         '!', '#', '$', '%', '&', '(', ')', '*', '+', '-',
  25         ';', '<', '=', '>', '?', '@', '^', '_', '`', '{',
  26         '|', '}', '~'
  27 };
  28
  29 static char de85[256];
  30 static void prep_base85(void)
  31 {
  32         int i;
  33         if (de85['Z'])
  34                 return;
  35         for (i = 0; i < ARRAY_SIZE(en85); i++) {
  36                 int ch = en85[i];
  37                 de85[ch] = i + 1;
  38         }
  39 }
  40
  41 int decode_85(char *dst, const char *buffer, int len)
  42 {
  43         prep_base85();
  44
  45         say2("decode 85 <%.*s>", len / 4 * 5, buffer);
  46         while (len) {
  47                 unsigned acc = 0;
  48                 int de, cnt = 4;
  49                 unsigned char ch;
  50                 do {
  51                         ch = *buffer++;
  52                         de = de85[ch];
  53                         if (--de < 0)
  54                                 return error("invalid base85 alphabet %c", ch);
  55                         acc = acc * 85 + de;
  56                 } while (--cnt);
  57                 ch = *buffer++;
  58                 de = de85[ch];
  59                 if (--de < 0)
  60                         return error("invalid base85 alphabet %c", ch);
  61                 /* Detect overflow. */
  62                 if (0xffffffff / 85 < acc ||
  63                     0xffffffff - de < (acc *= 85))
  64                         return error("invalid base85 sequence %.5s", buffer-5);
  65                 acc += de;
  66                 say1(" %08x", acc);
  67
  68                 cnt = (len < 4) ? len : 4;
  69                 len -= cnt;
  70                 do {
  71                         acc = (acc << 8) | (acc >> 24);
  72                         *dst++ = acc;
  73                 } while (--cnt);
  74         }
  75         say("\n");
  76
  77         return 0;
  78 }
  79
  80 void encode_85(char *buf, const unsigned char *data, int bytes)
  81 {
  82         say("encode 85");
  83         while (bytes) {
  84                 unsigned acc = 0;
  85                 int cnt;
  86                 for (cnt = 24; cnt >= 0; cnt -= 8) {
  87                         unsigned ch = *data++;
  88                         acc |= ch << cnt;
  89                         if (--bytes == 0)
  90                                 break;
  91                 }
  92                 say1(" %08x", acc);
  93                 for (cnt = 4; cnt >= 0; cnt--) {
  94                         int val = acc % 85;
  95                         acc /= 85;
  96                         buf[cnt] = en85[val];
  97                 }
  98                 buf += 5;
  99         }
 100         say("\n");
 101
 102         *buf = 0;
 103 }
 104
 105 #ifdef DEBUG_85
 106 int main(int ac, char **av)
 107 {
 108         char buf[1024];
 109
 110         if (!strcmp(av[1], "-e")) {
 111                 int len = strlen(av[2]);
 112                 encode_85(buf, av[2], len);
 113                 if (len <= 26) len = len + 'A' - 1;
 114                 else len = len + 'a' - 26 - 1;
 115                 printf("encoded: %c%s\n", len, buf);
 116                 return 0;
 117         }
 118         if (!strcmp(av[1], "-d")) {
 119                 int len = *av[2];
 120                 if ('A' <= len && len <= 'Z') len = len - 'A' + 1;
 121                 else len = len - 'a' + 26 + 1;
 122                 decode_85(buf, av[2]+1, len);
 123                 printf("decoded: %.*s\n", len, buf);
 124                 return 0;
 125         }
 126         if (!strcmp(av[1], "-t")) {
 127                 char t[4] = { -1,-1,-1,-1 };
 128                 encode_85(buf, t, 4);
 129                 printf("encoded: D%s\n", buf);
 130                 return 0;
 131         }
 132 }
 133 #endif