/easytag-2.1.7/src/base64.c

/*
 * Copyright (c) 1995 - 1999 Kungliga Tekniska H??gskolan
 * (Royal Institute of Technology, Stockholm, Sweden).
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * 3. Neither the name of the Institute nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/* (From RFC1521 and draft-ietf-dnssec-secext-03.txt)
   The following encoding technique is taken from RFC 1521 by Borenstein
   and Freed.  It is reproduced here in a slightly edited form for
   convenience.

   A 65-character subset of US-ASCII is used, enabling 6 bits to be
   represented per printable character. (The extra 65th character, "=",
   is used to signify a special processing function.)

   The encoding process represents 24-bit groups of input bits as output
   strings of 4 encoded characters. Proceeding from left to right, a
   24-bit input group is formed by concatenating 3 8-bit input groups.
   These 24 bits are then treated as 4 concatenated 6-bit groups, each
   of which is translated into a single digit in the base64 alphabet.

   Each 6-bit group is used as an index into an array of 64 printable
   characters. The character referenced by the index is placed in the
   output string.

                         Table 1: The Base64 Alphabet

      Value Encoding  Value Encoding  Value Encoding  Value Encoding
          0 A            17 R            34 i            51 z
          1 B            18 S            35 j            52 0
          2 C            19 T            36 k            53 1
          3 D            20 U            37 l            54 2
          4 E            21 V            38 m            55 3
          5 F            22 W            39 n            56 4
          6 G            23 X            40 o            57 5
          7 H            24 Y            41 p            58 6
          8 I            25 Z            42 q            59 7
          9 J            26 a            43 r            60 8
         10 K            27 b            44 s            61 9
         11 L            28 c            45 t            62 +
         12 M            29 d            46 u            63 /
         13 N            30 e            47 v
         14 O            31 f            48 w         (pad) =
         15 P            32 g            49 x
         16 Q            33 h            50 y

   Special processing is performed if fewer than 24 bits are available
   at the end of the data being encoded.  A full encoding quantum is
   always completed at the end of a quantity.  When fewer than 24 input
   bits are available in an input group, zero bits are added (on the
   right) to form an integral number of 6-bit groups.  Padding at the
   end of the data is performed using the '=' character.

   Since all base64 input is an integral number of octets, only the
         -------------------------------------------------
   following cases can arise:

       (1) the final quantum of encoding input is an integral
           multiple of 24 bits; here, the final unit of encoded
	   output will be an integral multiple of 4 characters
	   with no "=" padding,
       (2) the final quantum of encoding input is exactly 8 bits;
           here, the final unit of encoded output will be two
	   characters followed by two "=" padding characters, or
       (3) the final quantum of encoding input is exactly 16 bits;
           here, the final unit of encoded output will be three
	   characters followed by one "=" padding character.
   */

/* $Id: base64.c,v 1.5 2001/05/28 17:33:41 joda Exp $ */

/*
 * Code taken from Kerberos krb4-1.2.2
 */

#include <stdlib.h>
#include <string.h>
#include "base64.h"

/* Useful for encoding */
static char base64_chars[] = 
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

/* For constant time lookups */
static int
is_base64_char(char c)
{
    return (('A' <= c && c <= 'Z') || ('a' <= c && c <= 'z') || 
            ('0' <= c && c <= '9') || (c == '+' || c == '/'));
}

static int 
pos(char c)
{
    char *p;
    for (p = base64_chars; *p; p++)
	if (*p == c)
	    return p - base64_chars;
    return -1;
}

int 
base64_encode(const void *data, int size, char **str)
{
    char *s, *p;
    int i;
    int c;
    const unsigned char *q;

    p = s = (char *) malloc(size * 4 / 3 + 4);
    if (p == NULL)
        return -1;
    q = (const unsigned char *) data;
    i = 0;
    for (i = 0; i < size;)
    {
        c = q[i++];
        c *= 256;
        if (i < size)
            c += q[i];
        i++;
        c *= 256;
        if (i < size)
            c += q[i];
        i++;
        p[0] = base64_chars[(c & 0x00fc0000) >> 18];
        p[1] = base64_chars[(c & 0x0003f000) >> 12];
        p[2] = base64_chars[(c & 0x00000fc0) >> 6];
        p[3] = base64_chars[(c & 0x0000003f) >> 0];
        if (i > size)
            p[3] = '=';
        if (i > size + 1)
            p[2] = '=';
        p += 4;
    }
    *p = 0;
    *str = s;
    return strlen(s);
}

#define DECODE_ERROR ((unsigned) -1)

static unsigned int
token_decode(const char *token, const size_t size)
{
    int i;
    unsigned int val = 0;
    int marker = 0;
    
    if (size < 4)
        return DECODE_ERROR;
    for (i = 0; i < 4; i++)
    {
        val *= 64;
        if (token[i] == '=')
            marker++;
        else if (marker > 0)
            return DECODE_ERROR;
        else
            val += pos(token[i]);
    }
    if (marker > 2)
        return DECODE_ERROR;
    return (marker << 24) | val;
}

int
base64_decode(const char *str, void *data)
{
    const char     *p;
    unsigned char  *q;
    unsigned int    size;

    q = data;
    size = strlen(str);
    for (p = str; *p && (*p == '=' || is_base64_char(*p)); p += 4, size -= 4)
    {
        unsigned int val = token_decode(p, size);
        unsigned int marker = (val >> 24) & 0xff;
        
        if (val == DECODE_ERROR)
            return -1;
        *q++ = (val >> 16) & 0xff;
        if (marker < 2)
            *q++ = (val >> 8) & 0xff;
        if (marker < 1)
            *q++ = val & 0xff;
    }
    return q - (unsigned char *) data;
}