base64/base64.c at main · mayliex/base64 · GitHub

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#include <sys/types.h>

#include <stdio.h>
#include <string.h>

#define always_inline   inline __attribute__((always_inline))

struct slice_t {
    char * buf;
    size_t len;
    size_t cap;
};

/** Exported Functions **/

void   b64encode(struct slice_t *out, const struct slice_t *src);
size_t b64decode(struct slice_t *out, const char *src, size_t nb);

/** Encoder Helper Functions **/

static const char TabEncodeCharsetStd[64] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

static always_inline void encode(char *out, char *src, const char *tab) {
    out[0] = tab[(src[0] >> 2)];
    out[1] = tab[((src[0] << 4) & 0x30) | (src[1] >> 4)];
    out[2] = tab[((src[1] << 2) & 0x3C) | (src[2] >> 6)];
    out[3] = tab[src[2] & 0x3F];
}

static always_inline void encode_remainder(char *out, char *src, char *src_end, const char *tab) {
    out[0] = tab[(src[0] >> 2)];
    if (src+1 == src_end) { // 1 char left
        out[1] = tab[(src[0] << 4) & 0x30];
        out[2] = '=';
    } else { // 2 char left
        out[1] = tab[((src[0] << 4) & 0x30) | (src[1] >> 4)];
        out[2] = tab[(src[1] << 2) & 0x3C];
    }
    out[3] = '=';
}

/** Function Implementations **/
void b64encode(struct slice_t *out, const struct slice_t *src) {
    char *       out_start = out->buf + out->len;
    char *       out_i = out->buf + out->len;
    char *       src_i = src->buf;
    char *       src_end = src->buf + src->len;
    const char * st = TabEncodeCharsetStd;

    /* check for empty string */
    if (src->len == 0) {
        return;
    }

    /* converting 3 bytes to 4 bytes */
    while (src_i + 3 <= src_end) {
        encode(out_i, src_i, st);
        src_i += 3;
        out_i += 4;
    }

    /* converting 1/2 bytes to 4 bytes */
    if (src_i < src_end) {
        encode_remainder(out_i, src_i, src_end, st);
        src_i = src_end;
        out_i += 4;
    }

    /* update slice */
    out->len += out_i - out_start;
}

static const u_int8_t TabDecodeCharsetStd[128] = {
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x3e, 0x00, 0x00, 0x00, 0x3f,
    0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e,
    0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28,
    0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, 0x31, 0x32, 0x33, 0x00, 0x00, 0x00, 0x00, 0x00,
};

static always_inline void decode(char *out, char *src, const char *tab) {
    out[0] = (tab[src[0]] << 2) | ((tab[src[1]] >> 4) & 0x03);
    out[1] = (tab[src[1]] << 4) | (tab[src[2]] >> 2);
    out[2] = (tab[src[2]] << 6) | tab[src[3]];
}

size_t b64decode(struct slice_t *out, const char *src, size_t nb) {
    char *       out_start = out->buf + out->len;
    char *       out_i = out->buf + out->len;
    char *       src_end = src + nb;
    const char * st = TabDecodeCharsetStd;

    /* check for empty string */
    if (nb == 0) {
        return 0;
    }

    /* converting 4 bytes to 3 bytes */
    while (src + 4 <= src_end) {
        decode(out_i, src, st);
        src   += 4;
        out_i += 3;
    }

    return nb;
}

void test_encode() {
    struct slice_t src, out;
    char static_buf[] = "Hello";

    src.buf = static_buf;               // Указатель на строку
    src.len = strlen(static_buf);       // Длина строки
    src.cap = strlen(static_buf);       // sizeof Вместимость буфера (включая '\0')

    const int cap = ((sizeof(static_buf)/sizeof(char)) / 3) * 4;

    static char empty_buf[cap];
    out.buf = &empty_buf[0];
    out.len = 0;
    out.cap = cap;

    printf("src.Buffer: %s\n", src.buf);
    printf("src.Length: %zu\n", src.len);
    printf("src.Capacity: %zu\n", src.cap);

    b64encode(&out, &src);

    printf("Result: ");
    for (const char *p = out.buf; p < out.buf + out.len; p++) {
        printf("%c", *p);
    }
    printf("\n");

    printf("out.Buffer: %s\n", out.buf);
    printf("out.Length: %zu\n", out.len);
    printf("out.Capacity: %zu\n", out.cap);
}

void test_decode() {
    struct slice_t src, out;
    char static_buf[] = "SGVsbG8=";

    src.buf = static_buf;
    src.len = strlen(static_buf);
    src.cap = strlen(static_buf);

    const int cap = ((sizeof(static_buf)/sizeof(char)) / 4) * 3;

    char empty_buf[cap];
    out.buf = &empty_buf[0];
    out.len = 0;
    out.cap = cap;

    printf("Buffer: %s\n", src.buf);
    printf("Length: %zu\n", src.len);
    printf("Capacity: %zu\n", src.cap);

    b64decode(&out, src.buf, src.len);

    printf("Result: \n");
    for (const char *p = out.buf; p < out.buf + out.cap; p++) {
        printf("%c", *p);
    }
}


void main() {
    test_encode();
    test_decode();
}