Simple (and portable) Base64 implementation in C

b64test.c

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <stdint.h>
#include <string.h>
#include <time.h>

int countchr(char *str, char chr) {
    int i;
    for (i=0; *str != '\0'; *str++ == chr ? i++ : 0);
    return i;
}

size_t b64enclen(size_t datalen) {
    if (datalen % 3 == 0) return datalen / 3 * 4;
    else return (datalen + 3 - datalen % 3) / 3 * 4;
}

size_t b64declen(char *data) {
    size_t datalen;
    datalen = strlen(data);
    assert(datalen % 4 == 0);
    return datalen / 4 * 3 - countchr(data, '=');
}

int b64encode(void *in, size_t inlen, char *out, size_t outlen) {
    char B64CHR[] = 
        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
    char PAD = '=';
    uint8_t num3[3], num4[4], padnum, j;
    uint32_t tempnum;
    size_t i, outptr = 0;

    if (outlen < b64enclen(inlen)) return 1;

    for (i=0; i<inlen; i+=3) {
        num3[0] = ((uint8_t *)in)[i];

        if (inlen - i > 1)
            num3[1] = ((uint8_t *)in)[i+1];
        else
            num3[1] = 0;

        if (inlen - i > 2)
            num3[2] = ((uint8_t *)in)[i+2];
        else
            num3[2] = 0;

        tempnum = num3[0] << 16;
        tempnum += num3[1] << 8;
        tempnum += num3[2];

        num4[0] = (tempnum >> 18) & 63;
        num4[1] = (tempnum >> 12) & 63;
        num4[2] = (tempnum >> 6) & 63;
        num4[3] = tempnum & 63;

        for (j=0; j<4; j++) {
            out[outptr++] = B64CHR[num4[j]];
        }
    }

    if (inlen % 3 == 0) padnum = 0;
    else padnum = 3 - inlen % 3;

    for (i=0; i<padnum; i++) {
        out[--outptr] = PAD;
    }

    return 0;
}

int b64decode(char *in, size_t inlen, void *out, size_t outlen) {
    uint8_t B64TABLE[] = {
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 62, 0,
        0, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 0, 0, 0, 0, 0, 0, 0, 0, 1,
        2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21,
        22, 23, 24, 25, 0, 0, 0, 0, 63, 0, 26, 27, 28, 29, 30, 31, 32, 33, 34,
        35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
    };
    uint8_t num3[3], num4[4], j;
    uint32_t tempnum;
    size_t i, outptr = 0;

    i = b64declen(in);

    if (outlen < i) return 1;

    outlen = i;

    for (i=0; i<inlen; i += 4) {
        num4[0] = B64TABLE[(uint8_t)(in[i])];
        num4[1] = B64TABLE[(uint8_t)(in[i+1])];
        num4[2] = B64TABLE[(uint8_t)(in[i+2])];
        num4[3] = B64TABLE[(uint8_t)(in[i+3])];

        tempnum = (num4[0] & 63) << 18;
        tempnum += (num4[1] & 63) << 12;
        tempnum += (num4[2] & 63) << 6;
        tempnum += (num4[3] & 63);

        num3[0] = (tempnum >> 16) & 255;
        num3[1] = (tempnum >> 8) & 255;
        num3[2] = tempnum & 255;

        for (j=0; j<3 && outptr < outlen; j++) {
            ((uint8_t *)out)[outptr++] = num3[j];
        }

        if (outptr >= outlen) break;
    }

    return 0;
}

void fillrandom(void *buf, size_t bufsize) {
    size_t i;

    for (i=0; i<bufsize; i++)
        ((uint8_t *)buf)[i] = rand() % 255;

    return;
}

int main() {
    char teststr[] = "Aah! Natsu Wo Ima Mou Ikkai!", *in, *out;
    size_t inlen, outlen;

    inlen = sizeof(teststr) / sizeof(char);
    outlen = b64enclen(inlen);

    out = calloc(outlen + 1, sizeof(char));

    b64encode(teststr, inlen, out, outlen);

    printf("[*] %lu %lu %s %s\n", inlen, outlen, teststr, out);

    in = out;
    inlen = outlen;

    outlen = b64declen(in);
    out = calloc(inlen + 1, sizeof(char));

    b64decode(in, inlen, out, outlen);

    printf("[*] %lu %lu %s %s\n", inlen, outlen, in, out);

    free(in);
    free(out);

    int i;
    size_t origlen;
    void *origbuf;

    srand(time(NULL));

    for (i=0; 1; i++) {
        origlen = 1000 + rand() % 4000;
        origbuf = malloc(origlen);
        fillrandom(origbuf, origlen);

        outlen = b64enclen(origlen);
        out = calloc(outlen + 1, sizeof(char));

        b64encode(origbuf, origlen, out, outlen);

        in = out;
        inlen = outlen;

        outlen = b64declen(in);
        out = malloc(outlen);

        b64decode(in, inlen, out, outlen);

        //printf("[*] %lu %lu %lu %d\n", origlen, inlen, outlen, memcmp(origbuf, out, origlen));
        assert(origlen == outlen);
        assert(memcmp(origbuf, out, origlen) == 0);
        printf("%d passed\r", i);
        free(origbuf);
        free(in);
        free(out);
    }

    return 0;
}

gistfile1.txt

-------------------------------------------------
|       h       |       e       |       l       |
|0 1 1 0 1 0 0 0|0 1 1 0 0 1 0 1|0 1 1 0 1 1 0 0|
|0 1 1 0 1 0|0 0 0 1 1 0|0 1 0 1 0 1|1 0 1 1 0 0|
|     a     |     G     |     V     |     s     |
-------------------------------------------------

-------------------------------------------------------------------------------------------------
|       h       |       e       |       l       |       l       |       #       |       #       |
|0 1 1 0 1 0 0 0|0 1 1 0 0 1 0 1|0 1 1 0 1 1 0 0|0 1 1 0 1 1 0 0|# # # # # # # #|# # # # # # # #|
|0 1 1 0 1 0|0 0 0 1 1 0|0 1 0 1 0 1|1 0 1 1 0 0|0 1 1 0 1 1|0 0 0 0 0 0|# # # # # #|# # # # # #|
|     a     |     G     |     V     |     s     |     b     |     G     |     =     |     =     |
-------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------
|       h       |       e       |       l       |       l       |       o       |       #       |
|0 1 1 0 1 0 0 0|0 1 1 0 0 1 0 1|0 1 1 0 1 1 0 0|0 1 1 0 1 1 0 0|0 1 1 0 1 1 1 1|# # # # # # # #|
|0 1 1 0 1 0|0 0 0 1 1 0|0 1 0 1 0 1|1 0 1 1 0 0|0 1 1 0 1 1|0 0 0 1 1 0|1 1 1 1 0 0|# # # # # #|
|     a     |     G     |     V     |     s     |     b     |     G     |     8     |     =     |
-------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------
|       h       |       e       |       l       |       l       |       o       |       w       |
|0 1 1 0 1 0 0 0|0 1 1 0 0 1 0 1|0 1 1 0 1 1 0 0|0 1 1 0 1 1 0 0|0 1 1 0 1 1 1 1|0 1 1 1 0 1 1 1|
|0 1 1 0 1 0|0 0 0 1 1 0|0 1 0 1 0 1|1 0 1 1 0 0|0 1 1 0 1 1|0 0 0 1 1 0|1 1 1 1 0 1|1 1 0 1 1 1|
|     a     |     G     |     V     |     s     |     b     |     G     |     9     |     3     |
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