[loader] add ZBIC (zstd variant) NSO decompression support for Switch 22.0+ (#4482)

- [x] I have read and followed the [Contribution Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/CONTRIBUTING.md#code-contributions).
- [x] I have read and followed the [AI Policy](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/AI.md)
- [x] I have read and followed the [Coding Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/Coding.md) to the best of my ability.

-------------------
A new NSO compression method was introduced in Switch 22.0.0. This is a
customized variant of zstd and is used when NSO flags have bit 7 set.

Key characteristics:
  - ZSTD_MAGICNUMBER is set to 0x4349425A (b'ZBIC') instead of 0xFD2FB528
  - ZSTD_LEGACY_SUPPORT is set to 0
  - ZSTD_TRACE is set to 1, zstd version used is 1.5.7 (10507)
  - FSE_readNCount is replaced with a BIC (Binary Interpolative Coding)
    version which improves compression of entropy tables significantly

Source: https://switchbrew.org/wiki/22.0.0

Implementation:
  - Detect ZBIC segments via NSO flag bit 7 (NsoFlags_UseZbicCompression)
    and/or ZBIC magic scan in nso.cpp
  - Fall back to LZ4 when ZBIC is not detected or returns unexpected size
  - Handle segment 0 alternate offset (0x100 vs 0x108) for both ZBIC and LZ4

References:
  - Atmosphère loader/strat zstd-zbic integration:
    https://github.com/Atmosphere-NX/Atmosphere/commit/082115187a0509cb6b8a757de639a4e4741b8712
  - nxdumptool ZBIC segment compression support:
    https://github.com/DarkMatterCore/nxdumptool/commit/441e5c0904f29427987433be4eb057a2843d222a
  - STORM_SWITCH ZBIC implementation:
    https://github.com/ReiKatari/STORM_SWITCH/commit/1e09eb82b760aaf340b810031400991c0740c091

Tested with firmware 23.0.0 and ZBIC-compressed NSOs.

Co-authored-by: xbzk <xbzk@eden-emu.dev>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4482
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>
Reviewed-by: lizzie <lizzie@eden-emu.dev>
Reviewed-by: Maufeat <sahyno1996@gmail.com>

3 files changed, 67 insertions, 0 deletions

diff --git a/src/common/CMakeLists.txt b/src/common/CMakeLists.txt
index 0517f0b9e1..5d1b30a549 100644
--- a/src/common/CMakeLists.txt
+++ b/src/common/CMakeLists.txt
@@ -137,6 +137,8 @@ add_library(
     uuid.cpp
     uuid.h
     vector_math.h
+    zbic_compression.cpp
+    zbic_compression.h
     zstd_compression.cpp
     zstd_compression.h
     fs/ryujinx_compat.h fs/ryujinx_compat.cpp
@@ -147,6 +149,10 @@ add_library(
     net/net.h net/net.cpp
     container/unordered_map.h container/unordered_set.h)
 
+set_source_files_properties(zbic_compression.cpp PROPERTIES
+    INCLUDE_DIRECTORIES "${ZBIC_INCLUDE_DIR}"
+    COMPILE_OPTIONS "$<$<CXX_COMPILER_ID:Clang,GNU>:-Wno-unused-function;-Wno-missing-declarations;-Wno-shadow>")
+
 if(WIN32)
     target_sources(common PRIVATE windows/timer_resolution.cpp
         windows/timer_resolution.h)
diff --git a/src/common/zbic_compression.cpp b/src/common/zbic_compression.cpp
new file mode 100644
index 0000000000..5e0e4d947b
--- /dev/null
+++ b/src/common/zbic_compression.cpp
@@ -0,0 +1,46 @@
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include <cstring>
+
+#include "common/zbic_compression.h"
+
+#define ZSTD_ZBIC_SUPPORT 1
+#define ZSTDLIB_VISIBLE static
+#define ZSTDLIB_HIDDEN static
+#define ZSTDERRORLIB_VISIBLE static
+#define ZSTDERRORLIB_HIDDEN static
+#undef ZSTD_MULTITHREAD
+
+#if defined(__ANDROID__)
+#undef _GNU_SOURCE
+#endif
+
+#include "zstd.h"
+#define g_ZSTD_threading_useless_symbol g_ZSTD_zbic_threading_useless_symbol
+#include "zstd.c"
+#undef g_ZSTD_threading_useless_symbol
+
+namespace Common::Compression {
+
+bool IsZBIC(std::span<const u8> src) {
+    if (src.size() < sizeof(u32)) {
+        return false;
+    }
+    u32 magic = 0;
+    std::memcpy(&magic, src.data(), sizeof(u32));
+    return magic == ZSTD_MAGICNUMBER; // 0x4349425A ("ZBIC")
+}
+
+int DecompressDataZBIC(std::span<u8> dst, std::span<const u8> src) {
+    if (dst.empty() || src.empty()) {
+        return -1;
+    }
+    const size_t res = ZSTD_decompress(dst.data(), dst.size(), src.data(), src.size());
+    if (ZSTD_isError(res)) {
+        return -1;
+    }
+    return static_cast<int>(res);
+}
+
+} // namespace Common::Compression
diff --git a/src/common/zbic_compression.h b/src/common/zbic_compression.h
new file mode 100644
index 0000000000..c36a559388
--- /dev/null
+++ b/src/common/zbic_compression.h
@@ -0,0 +1,15 @@
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#pragma once
+
+#include <span>
+#include "common/common_types.h"
+
+namespace Common::Compression {
+
+[[nodiscard]] bool IsZBIC(std::span<const u8> src);
+
+[[nodiscard]] int DecompressDataZBIC(std::span<u8> dst, std::span<const u8> src);
+
+} // namespace Common::Compression