text: 
  /**
   * `decode.c' - b64
   *
   * copyright (c) 2014 joseph werle
   */
  
  #include <stdio.h>
  #include <stdlib.h>
  #include <ctype.h>
  
  unsigned char *
  b64_decode_ex (const char *, size_t, int *);
  
  
  unsigned char *
  b64_decode (const char *src, size_t len,int *decsize) {
    return b64_decode_ex(src, len, decsize);
  }
  
  unsigned char *
  b64_decode_ex (const char *src, size_t len, int *decsize) {
    int i = 0;
    int j = 0;
    int l = 0;
    size_t size = 0;
    unsigned char *dec = NULL;
    unsigned char buf[3];
    unsigned char tmp[4];
  
    // alloc
    dec = (unsigned char *) malloc(0);
    if (NULL == dec) { return NULL; }
  
    // parse until end of source
    while (len--) {
      // break if char is `=' or not base64 char
      if ('=' == src[j]) { break; }
      if (!(isalnum(src[j]) || '+' == src[j] || '/' == src[j])) { break; }
  
      // read up to 4 bytes at a time into `tmp'
      tmp[i++] = src[j++];
  
      // if 4 bytes read then decode into `buf'
      if (4 == i) {
        // translate values in `tmp' from table
        for (i = 0; i < 4; ++i) {
          // find translation char in `b64_table'
          for (l = 0; l < 64; ++l) {
            if (tmp[i] == b64_table[l]) {
              tmp[i] = l;
              break;
            }
          }
        }
  
        // decode
        buf[0] = (tmp[0] << 2) + ((tmp[1] & 0x30) >> 4);
        buf[1] = ((tmp[1] & 0xf) << 4) + ((tmp[2] & 0x3c) >> 2);
        buf[2] = ((tmp[2] & 0x3) << 6) + tmp[3];
  
        // write decoded buffer to `dec'
        dec = (unsigned char *) realloc(dec, size + 3);
        for (i = 0; i < 3; ++i) {
          dec[size++] = buf[i];
        }
  
        // reset
        i = 0;
      }
    }
  
    // remainder
    if (i > 0) {
      // fill `tmp' with `\0' at most 4 times
      for (j = i; j < 4; ++j) {
        tmp[j] = '\0';
      }
  
      // translate remainder
      for (j = 0; j < 4; ++j) {
          // find translation char in `b64_table'
          for (l = 0; l < 64; ++l) {
            if (tmp[j] == b64_table[l]) {
              tmp[j] = l;
              break;
            }
          }
      }
  
      // decode remainder
      buf[0] = (tmp[0] << 2) + ((tmp[1] & 0x30) >> 4);
      buf[1] = ((tmp[1] & 0xf) << 4) + ((tmp[2] & 0x3c) >> 2);
      buf[2] = ((tmp[2] & 0x3) << 6) + tmp[3];
  
      // write remainer decoded buffer to `dec'
      dec = (unsigned char *) realloc(dec, size + (i - 1));
      for (j = 0; (j < i - 1); ++j) {
        dec[size++] = buf[j];
      }
    }
  
    // Make sure we have enough space to add '\0' character at end.
    dec = (unsigned char *) realloc(dec, size + 1);
    dec[size] = '\0';
    // Return back the size of decoded string if demanded.
    if (decsize != NULL) *decsize = size;
    return dec;
  }
  