strengthened conditions for using workplace into fse table space

ensure that the structure layout is as expected.
will trigger an error if it changes in the future.

Another solution would be to use a union,
this would be cleaner and get rid of these static asserts.

However, in order to keep the current code unmodified,
it would be necessary to use an un-named unions.
And apparently, un-named unions are only possible on "recent" compilers (C99+).

diff --git a/lib/decompress/zstd_decompress.c b/lib/decompress/zstd_decompress.c
index e9fc3633193b29767910d8f5676373e81b298aa7..35ed7c59a8e326efcbfc9117b4d4dd3c89e92415 100644 (file)
--- a/lib/decompress/zstd_decompress.c
+++ b/lib/decompress/zstd_decompress.c
@@ -2203,8 +2203,13 @@ static size_t ZSTD_loadEntropy(ZSTD_entropyDTables_t* entropy,
     const BYTE* const dictEnd = dictPtr + dictSize;
 
     if (dictSize <= 8) return ERROR(dictionary_corrupted);
+    assert(MEM_readLE32(dict) == ZSTD_MAGIC_DICTIONARY);   /* dict must be valid */
     dictPtr += 8;   /* skip header = magic + dictID */
 
+    ZSTD_STATIC_ASSERT(offsetof(ZSTD_entropyDTables_t, LLTable) == 0);
+    ZSTD_STATIC_ASSERT(offsetof(ZSTD_entropyDTables_t, OFTable) == sizeof(entropy->LLTable));
+    ZSTD_STATIC_ASSERT(offsetof(ZSTD_entropyDTables_t, MLTable) == sizeof(entropy->LLTable) + sizeof(entropy->OFTable));
+    ZSTD_STATIC_ASSERT(offsetof(ZSTD_entropyDTables_t, hufTable) == sizeof(entropy->LLTable) + sizeof(entropy->OFTable) + sizeof(entropy->MLTable));
     ZSTD_STATIC_ASSERT(offsetof(ZSTD_entropyDTables_t, hufTable) >= HUF_DECOMPRESS_WORKSPACE_SIZE);
     {   void* const workspace = entropy;   /* use fse tables as temporary workspace; implies fse table precede huffTable at beginning of entropy */
         size_t const workspaceSize = offsetof(ZSTD_entropyDTables_t, hufTable);