File content as of revision 14:19c5f6151319:

//
// Base64 Encoding and Decoding
//
// @note Copyright © 2013 by Smartware Computing, all rights reserved.
//     Individuals may use this application for evaluation or non-commercial
//     purposes. Within this restriction, changes may be made to this application
//     as long as this copyright notice is retained. The user shall make
//     clear that their work is a derived work, and not the original.
//     Users of this application and sources accept this application "as is" and
//     shall hold harmless Smartware Computing, for any undesired results while
//     using this application - whether real or imagined.
//
// author David Smart, Smartware Computing
//
#ifndef WIN32
#include "mbed.h"
#else
#include "windows.h"
typedef unsigned int uint32_t;
#endif
#include "Base64.h"

static const char encoding_table[] = {
    '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', '+', '/'
};

static const int mod_table[] = {0, 2, 1};

Base64::Base64()
{
    decoding_table = NULL;
}

Base64::~Base64()
{
    if (decoding_table)
        free(decoding_table);
}


char * Base64::Encode(const char *data, size_t input_length, size_t *output_length)
{
    *output_length = 4 * ((input_length + 2) / 3);

    char *encoded_data = (char *)malloc(*output_length+1);  // often used for text, so add room for NULL
    if (encoded_data == NULL) return NULL;

    for (unsigned int i = 0, j = 0; i < input_length;) {

        uint32_t octet_a = i < input_length ? data[i++] : 0;
        uint32_t octet_b = i < input_length ? data[i++] : 0;
        uint32_t octet_c = i < input_length ? data[i++] : 0;

        uint32_t triple = (octet_a << 0x10) + (octet_b << 0x08) + octet_c;

        encoded_data[j++] = encoding_table[(triple >> 3 * 6) & 0x3F];
        encoded_data[j++] = encoding_table[(triple >> 2 * 6) & 0x3F];
        encoded_data[j++] = encoding_table[(triple >> 1 * 6) & 0x3F];
        encoded_data[j++] = encoding_table[(triple >> 0 * 6) & 0x3F];
    }

    for (int i = 0; i < mod_table[input_length % 3]; i++)
        encoded_data[*output_length - 1 - i] = '=';

    encoded_data[*output_length] = '\0';    // as a courtesy to text users
    return encoded_data;
}


char * Base64::Decode(const char *data, size_t input_length, size_t *output_length)
{
    if (decoding_table == NULL)
        build_decoding_table();

    if (input_length % 4 != 0) 
        return NULL;

    *output_length = input_length / 4 * 3;
    if (data[input_length - 1] == '=') (*output_length)--;
    if (data[input_length - 2] == '=') (*output_length)--;

    char *decoded_data = (char *)malloc(*output_length+1);  // often used for text, so add room for NULL
    if (decoded_data == NULL) 
        return NULL;

    for (unsigned int i = 0, j = 0; i < input_length;) {

        uint32_t sextet_a = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];
        uint32_t sextet_b = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];
        uint32_t sextet_c = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];
        uint32_t sextet_d = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];

        uint32_t triple = (sextet_a << 3 * 6)
                          + (sextet_b << 2 * 6)
                          + (sextet_c << 1 * 6)
                          + (sextet_d << 0 * 6);

        if (j < *output_length) 
            decoded_data[j++] = (triple >> 2 * 8) & 0xFF;
        if (j < *output_length) 
            decoded_data[j++] = (triple >> 1 * 8) & 0xFF;
        if (j < *output_length) 
            decoded_data[j++] = (triple >> 0 * 8) & 0xFF;
    }
    decoded_data[*output_length] = '\0';    // as a courtesy to text users
    return decoded_data;
}


void Base64::build_decoding_table()
{
    decoding_table = (char *)malloc(256);

    for (int i = 0; i < 64; i++)
        decoding_table[(unsigned char) encoding_table[i]] = i;
}