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


static 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 char *decoding_table = NULL;
static int mod_table[] = { 0, 2, 1 };


char *
base64_encode( const char *data,
               size_t input_length,
               size_t * output_length, char *encoded_data )
{

    int i, j;

    *output_length = 4 * ( ( input_length + 2 ) / 3 );

    // char *encoded_data = malloc(*output_length);
    // if (encoded_data == NULL) return NULL;

    for ( i = 0, j = 0; i < input_length; )
    {
        uint32_t octet_a = i < input_length ? ( unsigned char ) data[i++] : 0;
        uint32_t octet_b = i < input_length ? ( unsigned char ) data[i++] : 0;
        uint32_t octet_c = i < input_length ? ( unsigned char ) 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 ( i = 0; i < mod_table[input_length % 3]; i++ )
        encoded_data[*output_length - 1 - i] = '=';

    return encoded_data;
}


void
build_decoding_table(  )
{

    int i;

    decoding_table = malloc( 256 );

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

char *
base64_decode( const char *data, size_t input_length, size_t * output_length )
{
    int i, j;

    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 = malloc( *output_length );
    if ( decoded_data == NULL )
        return NULL;

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

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

    return decoded_data;
}



void
base64_cleanup(  )
{
    free( decoding_table );
}