git/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, const 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 de, cnt = 4;
  48                 unsigned char ch;
  49                 do {
  50                         ch = *buffer++;
  51                         de = de85[ch];
  52                         if (--de < 0)
  53                                 return error("invalid base85 alphabet %c", ch);
  54                         acc = acc * 85 + de;
  55                 } while (--cnt);
  56                 ch = *buffer++;
  57                 de = de85[ch];
  58                 if (--de < 0)
  59                         return error("invalid base85 alphabet %c", ch);
  60                 /*
  61                  * Detect overflow.  The largest
  62                  * 5-letter possible is "|NsC0" to
  63                  * encode 0xffffffff, and "|NsC" gives
  64                  * 0x03030303 at this point (i.e.
  65                  * 0xffffffff = 0x03030303 * 85).
  66                  */
  67                 if (0x03030303 < acc ||
  68                     0xffffffff - de < (acc *= 85))
  69                         return error("invalid base85 sequence %.5s", buffer-5);
  70                 acc += de;
  71                 say1(" %08x", acc);
  72
  73                 cnt = (len < 4) ? len : 4;
  74                 len -= cnt;
  75                 do {
  76                         acc = (acc << 8) | (acc >> 24);
  77                         *dst++ = acc;
  78                 } while (--cnt);
  79         }
  80         say("\n");
  81
  82         return 0;
  83 }
  84
  85 void encode_85(char *buf, const unsigned char *data, int bytes)
  86 {
  87         prep_base85();
  88
  89         say("encode 85");
  90         while (bytes) {
  91                 unsigned acc = 0;
  92                 int cnt;
  93                 for (cnt = 24; cnt >= 0; cnt -= 8) {
  94                         int ch = *data++;
  95                         acc |= ch << cnt;
  96                         if (--bytes == 0)
  97                                 break;
  98                 }
  99                 say1(" %08x", acc);
 100                 for (cnt = 4; cnt >= 0; cnt--) {
 101                         int val = acc % 85;
 102                         acc /= 85;
 103                         buf[cnt] = en85[val];
 104                 }
 105                 buf += 5;
 106         }
 107         say("\n");
 108
 109         *buf = 0;
 110 }
 111
 112 #ifdef DEBUG_85
 113 int main(int ac, char **av)
 114 {
 115         char buf[1024];
 116
 117         if (!strcmp(av[1], "-e")) {
 118                 int len = strlen(av[2]);
 119                 encode_85(buf, av[2], len);
 120                 if (len <= 26) len = len + 'A' - 1;
 121                 else len = len + 'a' - 26 + 1;
 122                 printf("encoded: %c%s\n", len, buf);
 123                 return 0;
 124         }
 125         if (!strcmp(av[1], "-d")) {
 126                 int len = *av[2];
 127                 if ('A' <= len && len <= 'Z') len = len - 'A' + 1;
 128                 else len = len - 'a' + 26 + 1;
 129                 decode_85(buf, av[2]+1, len);
 130                 printf("decoded: %.*s\n", len, buf);
 131                 return 0;
 132         }
 133         if (!strcmp(av[1], "-t")) {
 134                 char t[4] = { -1,-1,-1,-1 };
 135                 encode_85(buf, t, 4);
 136                 printf("encoded: D%s\n", buf);
 137                 return 0;
 138         }
 139 }
 140 #endif