gistfile1.c

int base64num(int ch) {
  if (ch == '=') return 0;
  if (ch == '/') return 63; // bug was these 
  if (ch == '+') return 62; // two lines
  if (ch >= 'a') return ch-'a'+26;
  if (ch >= 'A') return ch-'A';
  if (ch >= '0') return ch-'0'+52;
  return 0;
}

size_t base642raw(const char *input, size_t ilen, unsigned char *output, size_t olen)
{
   if (!ilen||ilen%4) return 0; // bad input
   size_t i,o,k;
   uint32_t n=0;
   int rem = 0;
   for(i=0,o=0;i<ilen && o+3<olen;i+=4) {
      n=(base64num(input[i])<<18)+(base64num(input[i+1])<<12)+(base64num(input[i+2])<<6)+base64num(input[i+3]);
      // decode 3 chars
      output[o]=(n>>16)&0xff; o++;
      output[o]=(n>>8)&0xff; o++;
      output[o]=n&0xff; o++;
   }
   // handle remainder
   for(k=ilen-4;k<ilen;k++) rem += (input[k]=='=');
   return o-rem;
}