base64 de/encode in C

base64.c

static const char b64[] = "\
ABCDEFGHIJKLMNOPQRSTUVWXYZ\
abcdefghijklmnopqrstuvwxyz\
0123456789+/";
static const unsigned char b64dec[] = {
 0,  0,  0,  0,  0,  0,  0,  0,   0,  0,  0,  0,  0,  0,  0,  0, //0x00
 0,  0,  0,  0,  0,  0,  0,  0,   0,  0,  0,  0,  0,  0,  0,  0, //0x10
 0,  0,  0,  0,  0,  0,  0,  0,   0,  0,  0, 62,  0,  0,  0, 63, //0x20
52, 53, 54, 55, 56, 57, 58, 59,  60, 61,  0,  0,  0,  0,  0,  0, //0x30
 0,  0,  1,  2,  3,  4,  5,  6,   7,  8,  9, 10, 11, 12, 13, 14, //0x40
15, 16, 17, 18, 19, 20, 21, 22,  23, 24, 25,  0,  0,  0,  0,  0, //0x50
 0, 26, 27, 28, 29, 30, 31, 32,  33, 34, 35, 36, 37, 38, 39, 40, //0x60
41, 42, 43, 44, 45, 46, 47, 48,  49, 50, 51,  0,  0,  0,  0,  0, //0x70
 0,  0,  0,  0,  0,  0,  0,  0,   0,  0,  0,  0,  0,  0,  0,  0, //0x80
 0,  0,  0,  0,  0,  0,  0,  0,   0,  0,  0,  0,  0,  0,  0,  0, //0x90
 0,  0,  0,  0,  0,  0,  0,  0,   0,  0,  0,  0,  0,  0,  0,  0, //0xa0
 0,  0,  0,  0,  0,  0,  0,  0,   0,  0,  0,  0,  0,  0,  0,  0, //0xb0
 0,  0,  0,  0,  0,  0,  0,  0,   0,  0,  0,  0,  0,  0,  0,  0, //0xc0
 0,  0,  0,  0,  0,  0,  0,  0,   0,  0,  0,  0,  0,  0,  0,  0, //0xd0
 0,  0,  0,  0,  0,  0,  0,  0,   0,  0,  0,  0,  0,  0,  0,  0, //0xe0
 0,  0,  0,  0,  0,  0,  0,  0,   0,  0,  0,  0,  0,  0,  0,  0  //0xf0
};

char * base64Encode(char *data, int len) {
  int blocks = (len + 2) / 3;
  int newlen = blocks * 4 + 1;
  char *result = malloc(newlen);
  char *resptr = result;
  int i;
  
  for (i = len / 3 ; i > 0 ; i--) {
    resptr[0] = b64[  (unsigned char)data[0]             >> 2 ];
    
    resptr[1] = b64[ ((unsigned char)data[0] &     0b11) << 4 
                    | (unsigned char)data[1]             >> 4 ];
    
    resptr[2] = b64[ ((unsigned char)data[1] &   0b1111) << 2 
                    | (unsigned char)data[2]             >> 6 ];
    
    resptr[3] = b64[  (unsigned char)data[2] & 0b111111       ];
    resptr += 4;
    data += 3;
  }
  
  if (len < blocks * 3 - 1) {
    resptr[0] = b64[  (unsigned char)data[0]             >> 2 ];
    
    resptr[1] = b64[ ((unsigned char)data[0] &     0b11) << 4 ];
    
    resptr[2] = '=';
    
    resptr[3] = '=';
    resptr += 4;
  } else if (len < blocks * 3) {
    resptr[0] = b64[  (unsigned char)data[0]             >> 2 ];
    
    resptr[1] = b64[ ((unsigned char)data[0] &     0b11) << 4 
                    | (unsigned char)data[1]             >> 4 ];
    
    resptr[2] = b64[ ((unsigned char)data[1] &   0b1111) << 2 ];
    
    resptr[3] = '=';
    resptr += 4;
  }
  
  *resptr = 0;
  return result;
}

char * base64Decode(char *text, int *outlen) {
  // this functions treats invalid characters as 'A'. deal with it :-P
  int inlen = (strlen(text) >> 2) << 2;
  int blocks = inlen >> 2;
  *outlen = blocks * 3 - (text[inlen-2] == '='
      ? 2 : (text[inlen-1] == '=' ? 1 : 0));
  char *result = malloc(blocks * 3);
  char *resptr = result;
  int i;
  
  for (i = 0 ; i < blocks ; i++) {
    resptr[0] = b64dec[text[0]] << 2 | b64dec[text[1]] >> 4;
    resptr[1] = b64dec[text[1]] << 4 | b64dec[text[2]] >> 2;
    resptr[2] = b64dec[text[2]] << 6 | b64dec[text[3]];
    
    text += 4;
    resptr += 3;
  }
  
  return result;
}