Is this a bug?

[masaoliou]

Use gcc to compile the following code and run it with command ./a.out -t, decode_85() goes to:
say1("invalid base85 alphabet (%c)\n",ch); return -1;

#include <string.h>
#include <stdio.h>
//#undef DEBUG_85
#define 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)
{
    if (de85['Z'])
        return;
    int i;
    for (i = 0; i < sizeof(en85); i++) {
        int ch = en85[i];
        de85[ch] = i + 1;
    }
}


int decode_85(char *dst, const char *buffer, int len)
{
const char *start=buffer;
    prep_base85();
    say2("decoding=>(given len=%d,converted len=%d)",len,len/4*5);
    say2(" decoding str:(%.*s)", len/4*5, buffer);
    while (len) {
say1("\n(loop len=%d) ",len);
        unsigned acc = 0;
        int de, cnt = 4;
        unsigned char ch;
        do {
            ch = *buffer++;
say1("%c",ch);
            de = de85[ch];
            if (--de < 0){
                //return error("invalid base85 alphabet %c", ch);
                say1("invalid base85 alphabet (%c)\n",ch); return -1;
            }
            acc = acc * 85 + de;
        } while (--cnt);
        ch = *buffer++;
say1("%c",ch);
        de = de85[ch];
        if (--de < 0){
            //return error("invalid base85 alphabet %c", ch);
            say("error -2\n"); return -2;
        }
        /* Detect overflow. */
        if (0xffffffff / 85 < acc || 0xffffffff - de < (acc *= 85)){
            //return error("invalid base85 sequence %.5s", buffer-5);
            say("error -3\n"); return -3;
        }
        acc += de;
        say1(" %08X", acc);
        cnt = (len < 4) ? len : 4;
        len -= cnt;
        do {
            acc = (acc << 8) | (acc >> 24);
            *dst++ = acc;
        } while (--cnt);
    }
    say1("\n",len);
    //return 0;
return buffer-start;
}

//#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;
        */
        char encoded[1024];
        char decoded[1024];
        const char instring[]="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZa";
        int encoded_len=encode_85(encoded,instring,strlen(instring));
        decode_85(decoded,encoded,encoded_len);
say2("inlen=%d,outlen=%d",strlen(instring),encoded_len);
say1("\n%s\n",decoded);
        return 0;
    }
}
//#endif