dune-savegame-variant

name	dune-savegame-variant
description	Identify the Dune (1992, Cryo) savegame version from the filename and select the correct field offsets. Use when: parsing or editing .SAV files, routing to the right offset table, detecting DUNE21/DUNE23/DUNE24/DUNE37/DUNE38 save formats, implementing version-aware savegame readers, handling SaveFileFormat enum, or deciding which offsets to apply. The repo focus is DUNE 3.7 (CD version).
argument-hint	Provide the .SAV filename or describe the version detection task

Dune Savegame Variant Detection

When to Use

• Parsing a .SAV file and need to know which offset table to apply
• Implementing version-aware savegame readers, editors, or converters
• Routing logic based on game version embedded in the filename
• Deciding whether a file is the primary repo target (DUNE 3.7 CD)

Filename Convention

The original game names saves with a fixed pattern:

DUNE{VERSION}S{SLOT}.SAV

Part	Meaning	Example
DUNE	Literal prefix	DUNE
{VERSION}	2-digit version code (no dot)	37 for v3.7
S	Literal separator	S
{SLOT}	Save slot number (0–N)	1
.SAV	Extension (uppercase on DOS)	.SAV

Examples: DUNE37S1.SAV, DUNE21S0.SAV, DUNE38S2.SAV

Version Code → Format Mapping

Filename version code	Format ID	Game release	Offset table	Notes
21	DUNE_21 or DUNE_23	v2.1 or v2.3 (floppy)	Dune21Offsets or Dune23Offsets	Ambiguous — see below
23	DUNE_23	v2.3	Dune23Offsets	Rare; mostly v2.3 writes DUNE21
24	DUNE_24	v2.4	Dune24Offsets
37	DUNE_37	v3.7 (CD — repo focus)	Dune37Offsets
38	DUNE_38	v3.8	Dune37Offsets (shared)	Byte-identical to DUNE_37

DUNE 3.8 shares the same field offsets as DUNE 3.7. There is no separate Dune38Offsets.

DUNE21 prefix ambiguity: Real v2.3 game installations write saves named DUNE21Sx.SAV, not DUNE23Sx.SAV. The filename code 21 cannot reliably distinguish v2.1 from v2.3. If precision is needed between these two sub-versions, uncompressed data length or known byte differences at specific offsets must be used.

Detection Algorithm

function detectFormat(filename):
    stem = basename(filename)   # always uppercase on DOS

    if stem starts with "DUNE":
        versionCode = stem[4:6]               # characters at index 4 and 5

        switch versionCode:
            "21" → return DUNE_21  # WARNING: may actually be v2.3 data (see ambiguity note)
            "23" → return DUNE_23
            "24" → return DUNE_24
            "37" → return DUNE_37
            "38" → return DUNE_38

    # No match — default to most common release
    return DUNE_37

No in-file version header exists. The compressed stream has no magic bytes that identify the game version. The filename is the only available signal.

Offset Tables by Field

All values are byte offsets into the uncompressed save data.

Field	DUNE_21	DUNE_23	DUNE_24	DUNE_37 / DUNE_38
Troops	19557	19577	19587	19657
Locations	17695	17615	17625	17695
NPCs	21393	21413	21423	21493
Smugglers	21393	21671	21681	21751
Charisma	17480	17480	17480	17480
ContactDistance	21909	21909	21909	21909
NumberOfRalliedTroops	17479	17479	17479	17479
GameStage	17481	17481	17481	17481
Spice	17599	17599	17599	17599
Dialogues	13113	13113	13113	13113

Offsets for DUNE_37 / DUNE_38 are verified against real save files. Offsets for earlier versions are partially unverified — use with caution. The main structural divergence across versions is in Troops, Locations, NPCs, and Smugglers.

Repo Focus: DUNE 3.7

This repository (OpenRakis) targets DUNE 3.7 as the primary version:

• It is the most widely distributed CD release.
• The reference save file in tests is DUNE37S1.SAV.
• DUNE 3.7 offsets are fully verified against real save files.
• When implementing new field reads, validate against DUNE 3.7 first.
• DUNE 3.8 is a minor variant with the same field layout as DUNE 3.7.

Decision Checklist

When starting work on any savegame field:

1. Extract the version code from the filename using the algorithm above.
2. Select the offset table from the mapping table.
3. If the version is DUNE 2.1 / 2.3 / 2.4, treat non-structural field offsets as unverified.
4. For DUNE 3.7 or 3.8, offsets are verified — use the DUNE 3.7 table for both.
5. If filename doesn't match the pattern, default to DUNE 3.7 and note the assumption.

Edge Cases

Situation	Handling
Version code not in known list	Warn; default to DUNE_37
Filename has no S{slot} suffix	Version code still extractable from chars 4–5
File was renamed by user	Version from filename may be wrong; document the ambiguity
DUNE38Sx.SAV	Use DUNE 3.7 offsets — byte-identical layout confirmed on real files
DUNE21Sx.SAV from v2.3 install	Filename says 21 but data uses v2.3 offsets; treat as ambiguous
Slot number	Slots start at 0 (S0), not 1 — DUNE37S0.SAV is a valid auto-save slot