base64 source code "bin to ascii"

/*----------------------------------------------------------------
 * base64_bin_to_ascii.c
 *
 * This source code is double license under:
 *   The MIT License (X11 License)
 *   Apache License, Version 2.0
 *
 * Copyright (c) 2013-2013 elf17 chobitprogram.blogspot.com All Rights Reserved.
 ----------------------------------------------------------------*/
/*----------------------------------------------------------------
 * The MIT License (MIT)
 * Copyright (c) 2013-2013 elf17 chobitprogram.blogspot.com
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom
 * the Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
 * KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS
 * OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
 * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 ----------------------------------------------------------------*/
/*----------------------------------------------------------------
 * Copyright elf17 chobitprogram.blogspot.com
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 ----------------------------------------------------------------*/

/**
 * convert 3 bytes binary to 4 bytes ascii + NULL terminator by base64.
 * @return status
 * @retval -1 : error charactor is found.
 * @retval  0 : success.
 * @retval  1 : detect end of data.
 * @see l64a()
 */
int b64a(const unsigned char * src, int len, unsigned char * dst)
{
    int ret = 0;                        /* return code */
    static const unsigned char b64str[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    unsigned char s[4] = {0};           /* src 8 bits + NULL terminator */
    unsigned char d[5] = {0};           /* dst 6 bits + NULL terminator */
    unsigned char f[4] = {1,1,1,1};     /* dst flag. true if src not exist. */
    int i = 0;                          /* loop counter */
    if ( len == 0 ) {
        dst[0] = 0;                     /* NULL terminator */
        ret = 1;                        /* detect end of data */
    } else {
        if ( len >= 1 ) {       s[0] = src[0]; f[0] = 0;       f[1] = 0;       }
        if ( len >= 2 ) {       s[1] = src[1]; f[1] = 0;       f[2] = 0;       }
        if ( len >= 3 ) {       s[2] = src[2]; f[2] = 0;       f[3] = 0;       }
        d[0] = (( s[0] & 0xfc ) >> 2);
        d[1] = (( s[0] & 0x03 ) << 4) | (( s[1] & 0xf0 ) >> 4 );
        d[2] = (( s[1] & 0x0f ) << 2) | (( s[2] & 0xc0 ) >> 6 );
        d[3] = (( s[2] & 0x3f )     );
        for ( i = 0 ; i < 4 ; i++ ) {
            if ( f[i] != 0 ) {          /* src not exist */
                dst[i] = '=';           /* NULL terminator */
                ret = 1;                /* detect end of data */
                /* no break ... output is always (4+1) bytes. */
            } else if ( d[i] >= 64 ) {  /* error data */
                dst[i] = 0;             /* NULL terminator */
                ret = -1;               /* error data */
                break;
            } else {
                dst[i] = b64str[d[i]];  /* convert to base64 string */
            }
        }
    }
    dst[4] = 0;                         /* NULL terminator */
    return ret;
}

/**
 * convert binary to ascii by base64.
 * @return status
 * @retval -1 : error charactor is found.
 * @retval  0 : success.
 * @see l64a(), b64a()
 */
int base64_bin_to_ascii(const unsigned char * src, int len, unsigned char * dst)
{
    int ret = 0;                        /* return code */
    const unsigned char * s = src;
    unsigned char * d = dst;
    int i = 0;                          /* loop counter */
    for ( i = 0 ; i < len ;  i += 3, s += 3, d += 4 ) {
        ret = b64a( s, (len - i), d );
        if ( ret != 0 ) {
            break;
        }
    }
    /* if error */
    if ( ret < 0 ) {
        dst[0] = 0;
    } else if ( ret > 0 ) {
        ret = 0;
    }
    return ret;
}