SARC

SARCs are archive files.

Structure

The basic structure of SARC files is documented on the MK8 wiki.

Hash algorithm

The algorithm given on the MK8 wiki is not fully correct: it fails to account for the fact that Nintendo's algorithm uses an unsigned 32-bit integer for the hash variable, and a signed char variable.

Here is more accurate implementation of the algorithm, written in C++:

const uint32_t multiplier = 0x65;
const char* string = "月クッパ戦Lv3(クリア後).baglshpp";
uint32_t hash = 0;
int i = 0;
while (true) {
  char c = string[i++]; // *signed* char
  if (!c)
    break;
  hash = hash * multiplier + c;
}

It appears that Nintendo's compiler treats a char as a signed type.

Usage in Breath of the Wild

SARCs are used extensively in Breath of the Wild to keep related data in memory and minimise loading times.

Extensions

Archives have a wide range of extensions. However, the file format is completely the same regardless of the extension.

The following extensions are specific to the game:

• pack
• bactorpack
• bmodelsh
• beventpack
• stera
• stats

The following extensions are used by Nintendo libraries that are included in the game (non exhaustive list):

• sarc
• bgenv
• genvb
• blarc

Data alignment

Some files have specific alignment requirements (e.g. for GPU data). Because Nintendo's SARC library returns file data by giving pointers to the data section directly, special care must be taken to pack files in a way that satisfies all alignment requirements.

Nintendo libraries do not use BotW's resource system and expect files to be properly aligned. This is the case for layout archives (blarc) and agl environment files (Pack/Bootup.pack/Env/env.genvb).

However unlike most other Nintendo games, for files that are managed by the game's resource system, aligning archive file data is usually unnecessary because the system will automatically allocate an aligned buffer and copy the archive data into it.

Tools

Because of the alignment problem and file size limitations due to Breath of the Wild's resource system, only the following tools are recommended:

Tool	Cross-platform	Setup	Known issues
SARC Tool	Yes	Install the sarclib package. [CLI help] Install the libyaz0 package. [CLI help] Download the latest release from GitHub.	Unnecessary padding for BotW: SARC Tool may add unnecessary padding when archives are repacked, meaning generated archives may end up larger than the original even if no file size has increased inside the SARC. The game will fail to load it unless you fix the Resource system.
sarc	Yes	Install the sarc package. [CLI help]	None
BotW Unpacker	Yes	Download the latest release from GitHub.	Wii U only: This tool can only handle big endian archives. Switch SARCs will not work as they use little endian.
Wild Bits	Yes	Ensure you have a 64 bit version of Python 3.7+ before continuing. Windows users must also install the latest x64 Visual C++ redistributable. You will not be able to install or launch Wild Bits otherwise. See Help:Setting_up_tools. (Optional) For best results on Windows, install cefpython3. [CLI help] Install the wildbits package. [CLI help]	On some system configurations, launching with wildbits doesn't work and you must use python -m wildbits instead.
Switch Toolbox	No	Simply download the latest compiled release from GitHub, unzip, and launch the exe. Note that the latest release has an old date, but it is current, as it automatically rebuilds with each commit.

We strongly advise against using other tools because they do not handle file alignment properly.