base64.c

char BASE64_ILUT[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
char BASE64_LUT[256];

void init_base64_lut(void) {
  int i;
  
  for (i = 0; i < 256; i++) {
    BASE64_LUT[i] = 255;
  }

  for (i = 0; i < 64; i++) {
    BASE64_LUT[BASE64_ILUT[i]] = i;
  }
}