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Most 7z folders are a single plain LZMA2 coder (7-Zip default -m0=lzma2 -ms=on). For that shape the facade now drives the SDK's own parallel decoder (Lzma2DecMt, vendored with MtDec/Threads) instead of the single-threaded chain walk; the chain stays responsible for every other shape (BCJ2 stacks, encrypted folders, exotic methods) and as the fallback when the platform cannot provide threads (SZ_ERROR_THREAD downgrades, never fails). Adapters: ISeqInStream over the read_at callback, ISeqOutStream into the staging sink (runs on the calling thread, so the sink contract is unchanged), ICompressProgress polling the cancel hook. The folder CRC is taken over the decoded stream as before. 329 MiB fixture, internal timing: 1050 ms (asm, 1 thread) -> 930 ms (4 threads) -> 765 ms (8 threads + 1 MiB inBufSize_MT), i.e. 1.37x, now at parity with 7za -mmt=off (898 ms); 7za -mmt=8 is 485 ms. The PS5 count is 8 Zen 2 cores like the dev host; SZX_MT_THREADS=8. Test matrices: 7z 28 + ZIP 108 + RAR 27 checks green.
7z decoder sources (LZMA SDK)
Vendored subset of the LZMA SDK 26.03 (2026-09-03) by Igor Pavlov.
Public domain — see DOC/lzma-sdk.txt:
LZMA SDK is written and placed in the public domain by Igor Pavlov.
Upstream: https://www.7-zip.org/sdk.html — release archive
lzma2603.7z from https://github.com/ip7z/7zip/releases.
These files back the 7z branch of the extraction engine (src/sevenz_*.c).
The SDK ships both a C and a C++ implementation; only the C one is used
here, because it builds with the plain prospero-clang C toolchain on PS5 and
has no dependency on the C++ runtime.
What is vendored
| Group | Files |
|---|---|
| container | 7z.h, 7zArcIn.c, 7zDec.c |
| streams / infra | 7zTypes.h, 7zStream.c, 7zFile.c, 7zAlloc.c, 7zBuf.c, 7zBuf2.c, Alloc.c |
| checksums | 7zCrc.c, 7zCrcOpt.c, SwapBytes.c |
| CPU / portability | CpuArch.c, Compiler.h, Precomp.h, RotateDefs.h, 7zWindows.h |
| codecs | LzmaDec.c, Lzma2Dec.c, Ppmd7.c, Ppmd7Dec.c, Ppmd.h, Bcj2.c, Bra.c, Bra86.c, BraIA64.c, Delta.c |
| crypto | Aes.c, AesOpt.c, Sha256.c, Sha256Opt.c |
| misc | DllSecur.c (only referenced by the Windows path of 7zFile.c), 7zVersion.h |
The encoder half of the SDK (LzmaEnc.c, Lzma2Enc.c, Xz*.c, Sort.c,
Threads.c, Mt*.c, Ppmd*Enc.c, …) is deliberately not vendored: the
engine only ever decodes.
Build flags that matter:
-DZ7_PPMD_SUPPORT— without it7zDec.cdrops the PPMd coder entirely.-D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE-w— the sources are not expected to be warning clean.
Known SDK limitations the engine has to work around
Both were confirmed empirically against real 7-Zip 26.03 output, see
tests/sevenz_e2e.c and tests/make_sevenz_fixtures.py.
1. CSzFolder caps a folder at 4 coders / 3 bonds
7z.h defines SZ_NUM_CODERS_IN_FOLDER_MAX 4 and
SZ_NUM_BONDS_IN_FOLDER_MAX 3, and SzGetNextFolderItem() refuses anything
larger. But the chain 7-Zip produces for -m0=bcj2 is BCJ2 + 4×LZMA2 = 5
coders / 4 bonds, so SzAr_DecodeFolder() returns SZ_ERROR_UNSUPPORTED on
an archive that 7-Zip itself created without complaint.
Note this only affects decoding: SzArEx_Open() parses folder blobs with a
separate, far more permissive scanner (k_Scan_NumCoders_MAX 64, in
7zArcIn.c), so the file list and all unpack sizes are still correct — the
failure shows up per-entry, at extract time.
Consequence: the engine parses folder blobs with its own dynamic parser and
drives the codec chain itself instead of calling SzAr_DecodeFolder().
2. There is no 7zAES coder in the C decoder
IS_SUPPORTED_CODER() in 7zDec.c accepts only Copy, LZMA, LZMA2,
PPMd and the branch/delta/BCJ2 filters. Aes.c is present but never wired
up, so both -p<password> archives and -mhe=on (encrypted header) archives
are rejected.
Consequence: the engine implements the 7zAES coder itself on top of the
vendored Aes.c / Sha256.c. The reference implementation is in the SDK's
C++ tree at CPP/7zip/Crypto/7zAes.cpp (not vendored, kept in the SDK tarball):
- properties:
b0 & 0x3F= numCyclesPower,b0 bit7andb1>>4add to the salt size,b0 bit6andb1 & 0x0Fadd to the IV size - key:
SHA-256(salt || password_utf16le || counter_le64)iterated1 << numCyclesPowertimes, unlessnumCyclesPower == 0x3Fin which case the key issalt || passwordtruncated/zero-padded to 32 bytes - then AES-256-CBC with that key and the (zero-padded) IV
Regenerating this directory
curl -L -o lzma2603.7z https://github.com/ip7z/7zip/releases/download/26.03/lzma2603.7z
7zr x lzma2603.7z -osdk
# copy the files listed above out of sdk/C/
tests/run-sevenz-tests.sh builds this subset and runs the fixture matrix.