root/base85.c

DEFINITIONS

1. prep_base85
2. decode_85
3. encode_85
4. main

#include "cache.h"

#undef DEBUG_85

#ifdef DEBUG_85
#define say(a) fprintf(stderr, a)
#define say1(a,b) fprintf(stderr, a, b)
#define say2(a,b,c) fprintf(stderr, a, b, c)
#else
#define say(a) do { /* nothing */ } while (0)
#define say1(a,b) do { /* nothing */ } while (0)
#define say2(a,b,c) do { /* nothing */ } while (0)
#endif

static const char en85[] = {
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
        'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
        'U', 'V', 'W', 'X', 'Y', 'Z',
        'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
        'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
        'u', 'v', 'w', 'x', 'y', 'z',
        '!', '#', '$', '%', '&', '(', ')', '*', '+', '-',
        ';', '<', '=', '>', '?', '@', '^', '_', '`', '{',
        '|', '}', '~'
};

static char de85[256];
static void prep_base85(void)
{
        int i;
        if (de85['Z'])
                return;
        for (i = 0; i < ARRAY_SIZE(en85); i++) {
                int ch = en85[i];
                de85[ch] = i + 1;
        }
}

int decode_85(char *dst, const char *buffer, int len)
{
        prep_base85();

        say2("decode 85 <%.*s>", len / 4 * 5, buffer);
        while (len) {
                unsigned acc = 0;
                int de, cnt = 4;
                unsigned char ch;
                do {
                        ch = *buffer++;
                        de = de85[ch];
                        if (--de < 0)
                                return error("invalid base85 alphabet %c", ch);
                        acc = acc * 85 + de;
                } while (--cnt);
                ch = *buffer++;
                de = de85[ch];
                if (--de < 0)
                        return error("invalid base85 alphabet %c", ch);
                /* Detect overflow. */
                if (0xffffffff / 85 < acc ||
                    0xffffffff - de < (acc *= 85))
                        return error("invalid base85 sequence %.5s", buffer-5);
                acc += de;
                say1(" %08x", acc);

                cnt = (len < 4) ? len : 4;
                len -= cnt;
                do {
                        acc = (acc << 8) | (acc >> 24);
                        *dst++ = acc;
                } while (--cnt);
        }
        say("\n");

        return 0;
}

void encode_85(char *buf, const unsigned char *data, int bytes)
{
        say("encode 85");
        while (bytes) {
                unsigned acc = 0;
                int cnt;
                for (cnt = 24; cnt >= 0; cnt -= 8) {
                        unsigned ch = *data++;
                        acc |= ch << cnt;
                        if (--bytes == 0)
                                break;
                }
                say1(" %08x", acc);
                for (cnt = 4; cnt >= 0; cnt--) {
                        int val = acc % 85;
                        acc /= 85;
                        buf[cnt] = en85[val];
                }
                buf += 5;
        }
        say("\n");

        *buf = 0;
}

#ifdef DEBUG_85
int main(int ac, char **av)
{
        char buf[1024];

        if (!strcmp(av[1], "-e")) {
                int len = strlen(av[2]);
                encode_85(buf, av[2], len);
                if (len <= 26) len = len + 'A' - 1;
                else len = len + 'a' - 26 - 1;
                printf("encoded: %c%s\n", len, buf);
                return 0;
        }
        if (!strcmp(av[1], "-d")) {
                int len = *av[2];
                if ('A' <= len && len <= 'Z') len = len - 'A' + 1;
                else len = len - 'a' + 26 + 1;
                decode_85(buf, av[2]+1, len);
                printf("decoded: %.*s\n", len, buf);
                return 0;
        }
        if (!strcmp(av[1], "-t")) {
                char t[4] = { -1,-1,-1,-1 };
                encode_85(buf, t, 4);
                printf("encoded: D%s\n", buf);
                return 0;
        }
}
#endif