Save file container format

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This page describes the container format used by Arx Fatalis save files (.sav) as well as Arx Libertatis extensions to that format.

See Common file format types for a description of the type names used here.

Save files are stored in a generic container that maps names (arbitrary strings) to chunks of data. Arx Libertatis adds two extensions to the vanilla Arx Fatalis .sav format. The .sav container format can be read and written using the SaveBlock class (io/SaveBlock.h)

Header

The file header starts at byte position 0 - there is no magic number.

Type Description
u32 File table offset

The file table offset is the location of the file table (in bytes) relative to the first byte after the header. Add 4 bytes to get the offset relative to the start of the file.

File table

The file table starts with a file table header:

File table header

Type Description
u32 Format version
u32 Number of file entries

Currently, the following version numbers are defined.

Value Name Description
0x00010000 SAV_VERSION_LEGACY Legacy version
0x00010001 SAV_VERSION_RELEASE Version used in Arx Fatalis 1.21
0x00020000 SAV_VERSION_DEFLATE Added support for different compression algorithms (Arx Libertatis extension)
0x00020001 SAV_VERSION_NOEXT Removed ".sav" suffix from internal filenames (Arx Libertatis extension)

The file table is followed by the specified number of file entries. For save files with version SAV_VERSION_LEGACY the first file entry should be ignored.

File table entries

Type Description
c string Filename

Each file table entry is preceded by a null-terminated string - the file name. Versions older than SAV_VERSION_NOEXT store file names case-insensitively and append ".sav". When loading such versions, the filename should be converted to lowercase and the ".sav" extension removed.

For versions older than SAV_VERSION_DEFLATE:

Type Description
u32 Stored (compressed) file size - This can be ignored and calculated from chunk sizes.
u32 Number of chunks - 0 means 1!
u32 Useless data. This can be safely ignored

For SAV_VERSION_DEFLATE and newer:

Type Description
u32 Uncompressed file size
u32 Number of chunks
u32 Compression algorithm

Currently, the following compression algorithms are defined.

Value Name Description
0 Stored No compression. Data is stored as-is.
1 ImplodeCrypt Data is compressed using the PKWARE implode library. Even-numbered bytes of the result are bitwise negated.
2 Deflate Data is compressed using the ZLIB deflate format.

Code to decompress PKWARE implode-encoded data can be found in blast.c in the contrib directory of the zlib source.

Versions older than SAV_VERSION_DEFLATE always use the ImplodeCrypt algorithm. To allow changing save files without decompressing all data, the value 0xffffffff may be used to indicate that the uncompressed size is not known if (and only if) the compression algorithm is ImplodeCrypt.

The rest of the file entry is a list of as many chunk offsets as specified. For versions older than SAV_VERSION_DEFLATE, the actual number of chunks is always 1 or more, even if the file entry says 0. The concatenation of the chunks referenced by these offsets makes up the compressed file data.

Chunk offsets

Type Description
u32 Chunk size
u32 Chunk offset

The chunk offset is the location of the chunk data (in bytes) relative to the first byte after the header. Add 4 bytes to get the offset relative to the start of the file. The chunk size is given in bytes. There is no guarantee that all parts of the .sav file are used in chunks or the file table.