#include <stdint.h>
#include <stdlib.h>

size_t b64_encoded_size(size_t inlen)
{
    size_t ret;

    ret = inlen;
    if (inlen % 3 != 0)
        ret += 3 - (inlen % 3);
    ret /= 3;
    ret *= 4;

    return ret;
}

const char b64chars[] = {'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', '0', '1', '2', '3',
                        '4', '5', '6', '7', '8', '9', '+', '/'};

char *b64_encode(const unsigned char *in, size_t len)
{
    char   *out;
    size_t  elen;
    size_t  i;
    size_t  j;
    size_t  v;

    if (in == NULL || len == 0)
        return NULL;

    elen = b64_encoded_size(len);
    out  = malloc(elen+1);
    out[elen] = '\0';

    for (i=0, j=0; i<len; i+=3, j+=4) {
        v = in[i];
        v = i+1 < len ? v << 8 | in[i+1] : v << 8;
        v = i+2 < len ? v << 8 | in[i+2] : v << 8;

        out[j]   = b64chars[(v >> 18) & 0x3F];
        out[j+1] = b64chars[(v >> 12) & 0x3F];
        if (i+1 < len) {
            out[j+2] = b64chars[(v >> 6) & 0x3F];
        } else {
            out[j+2] = '=';
        }
        if (i+2 < len) {
            out[j+3] = b64chars[v & 0x3F];
        } else {
            out[j+3] = '=';
        }
    }

    return out;
}

size_t b64_decoded_size(const char *in)
{
    size_t len;
    size_t ret;
    size_t i;

    if (in == NULL)
        return 0;

    len = strlen(in);
    ret = len / 4 * 3;

    for (i=len; i-->0; ) {
        if (in[i] == '=') {
            ret--;
        } else {
            break;
        }
    }

    return ret;
}

int b64invs[] = { 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58,
    59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 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, -1, -1, -1, -1, -1, -1, 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 
};



int b64_isvalidchar(char c)
{
    if (c >= '0' && c <= '9')
        return 1;
    if (c >= 'A' && c <= 'Z')
        return 1;
    if (c >= 'a' && c <= 'z')
        return 1;
    if (c == '+' || c == '/' || c == '=')
        return 1;
    return 0;
}

int b64_decode(const char *in, unsigned char *out, size_t outlen)
{
    size_t len;
    size_t i;
    size_t j;
    int    v;

    if (in == NULL || out == NULL)
        return 0;

    len = strlen(in);
    if (outlen < b64_decoded_size(in) || len % 4 != 0)
        return 0;

    for (i=0; i<len; i++) {
        if (!b64_isvalidchar(in[i])) {
            return 0;
        }
    }

    for (i=0, j=0; i<len; i+=4, j+=3) {
        v = b64invs[in[i]-43];
        v = (v << 6) | b64invs[in[i+1]-43];
        v = in[i+2]=='=' ? v << 6 : (v << 6) | b64invs[in[i+2]-43];
        v = in[i+3]=='=' ? v << 6 : (v << 6) | b64invs[in[i+3]-43];

        out[j] = (v >> 16) & 0xFF;
        if (in[i+2] != '=')
            out[j+1] = (v >> 8) & 0xFF;
        if (in[i+3] != '=')
            out[j+2] = v & 0xFF;
    }

    return 1;
}