loader/util: fully implement zstd bic variant

Implement both compression and decompression utilities and simplify loader logic

libraries/libstratosphere/source/util/util_compression.cpp

@@ -15,6 +15,9 @@
  */
 #include <stratosphere.hpp>
 #include "lz4.h"
+#define ZSTD_STATIC_LINKING_ONLY
+#define ZSTD_ZBIC_SUPPORT 1
+#include "zstd.h"
 
 namespace ams::util {
 
@@ -27,6 +30,23 @@ namespace ams::util {
         /* This is just a thin wrapper around LZ4. */
         return LZ4_compress_default(reinterpret_cast<const char *>(src), reinterpret_cast<char *>(dst), static_cast<int>(src_size), static_cast<int>(dst_size));
     }
+    
+    size_t CompressZstd(void *dst, size_t dst_size, const void *src, size_t src_size) {
+        /* Basic size checks. */
+        AMS_ABORT_UNLESS(dst_size <= std::numeric_limits<int>::max());
+        AMS_ABORT_UNLESS(src_size <= std::numeric_limits<int>::max());
+        
+        /* Additionally, we must check the compression boundary. */ 
+        auto bound = ZSTD_compressBound(src_size);
+        AMS_ABORT_UNLESS(!ZSTD_isError(bound));
+        AMS_ABORT_UNLESS(dst_size >= bound);
+
+        /* Use Zstd default level. */
+        int compressionLevel = 3;
+        
+        /* This is just a wrapper around Zstd. */
+        return ZSTD_compress(dst, dst_size, src, src_size, compressionLevel);
+    }
 
     /* Decompression utilities. */
     int DecompressLZ4(void *dst, size_t dst_size, const void *src, size_t src_size) {
@@ -37,5 +57,54 @@ namespace ams::util {
         /* This is just a thin wrapper around LZ4. */
         return LZ4_decompress_safe(reinterpret_cast<const char *>(src), reinterpret_cast<char *>(dst), static_cast<int>(src_size), static_cast<int>(dst_size));
     }
+    
+    size_t DecompressZstd(void *dst, size_t dst_size, const void *src, size_t src_size) {
+        /* Basic size checks. */
+        AMS_ABORT_UNLESS(dst_size <= std::numeric_limits<int>::max());
+        AMS_ABORT_UNLESS(src_size <= std::numeric_limits<int>::max());
+        
+        /* Additionally, we must check the decompression boundary. */ 
+        auto bound = ZSTD_decompressBound(src, src_size);
+        AMS_ABORT_UNLESS(!ZSTD_isError(bound));
+        AMS_ABORT_UNLESS(dst_size >= bound);
+        
+        /* This is just a wrapper around Zstd. */
+        return ZSTD_decompress(dst, dst_size, src, src_size);
+    }
+    
+    bool DecompressZstdForLoader(void* workspace, size_t workspace_size, void *dst, size_t dst_size, size_t expected_dec_size, const void *src, size_t src_size) {
+        /* Check decompression margin. */
+        auto margin = ZSTD_decompressionMargin(src, src_size);
+        if (ZSTD_isError(margin)) {
+            return false;
+        }
+        
+        /* Don't overflow from margin. */
+        if (!util::CanAddWithoutOverflow(margin, expected_dec_size)) {
+            return false;
+        }
+        
+        /* Make sure we fit in the destination buffer. */
+        if (margin + expected_dec_size > dst_size) {
+            return false;
+        }
+        
+        /* This is a runtime assert in Loader code. We replicate it here. */
+        AMS_ABORT_UNLESS(ZSTD_estimateDCtxSize() == workspace_size);
+        
+        /* Decompress using a static decompression context. */
+        auto dctx = ZSTD_initStaticDCtx(workspace, workspace_size);
+        size_t dec_size = ZSTD_decompressDCtx(dctx, dst, dst_size, src, src_size);
+
+        if (ZSTD_isError(dec_size)) {
+            return false;
+        }
+        
+        if (dec_size != expected_dec_size) {
+            return false;
+        }
+        
+        return true;
+    }
 
 }