CR fixes and better entropy for hash salt

Author: yoniko

lib/compress/zstd_compress.c

@@ -1939,7 +1939,8 @@ ZSTD_reset_matchState(ZSTD_matchState_t* ms,
          * 0 when we reset a Cdict */
         if(forWho == ZSTD_resetTarget_CCtx) {
             ms->tagTable = (U16 *) ZSTD_cwksp_reserve_aligned_init_once(ws, tagTableSize);
-            ms->hashSalt = ms->hashSalt * 6364136223846793005 + 1; /* based on MUSL rand */
+            ms->hashSalt = ZSTD_hashPtr(&ms->hashSalt, 32, sizeof(ms->hashSalt)) << 32 |
+                           ZSTD_hashPtr(&ms->hashSaltEntropy, 32, sizeof(ms->hashSaltEntropy));
         } else {
             /* When we are not salting we want to always memset the memory */
             ms->tagTable = (U16 *) ZSTD_cwksp_reserve_aligned(ws, tagTableSize);

lib/compress/zstd_compress_internal.h

@@ -228,7 +228,8 @@ struct ZSTD_matchState_t {
     U32 rowHashLog;                          /* For row-based matchfinder: Hashlog based on nb of rows in the hashTable.*/
     U16* tagTable;                           /* For row-based matchFinder: A row-based table containing the hashes and head index. */
     U32 hashCache[ZSTD_ROW_HASH_CACHE_SIZE]; /* For row-based matchFinder: a cache of hashes to improve speed */
-    U64 hashSalt;
+    U64 hashSalt;                            /* For row-based matchFinder: salts the hash for re-use of tag table */
+    U32 hashSaltEntropy;                     /* For row-based matchFinder: collects entropy for salt generation */
 
     U32* hashTable;
     U32* hashTable3;
@@ -845,7 +846,7 @@ size_t ZSTD_hashPtrSalted(const void* p, U32 hBits, U32 mls, const U64 hashSalt)
     switch(mls)
     {
         default:
-        case 4: return ZSTD_hash4PtrS(p, hBits, (U32)(hashSalt >> 32));
+        case 4: return ZSTD_hash4PtrS(p, hBits, (U32)hashSalt);
         case 5: return ZSTD_hash5PtrS(p, hBits, hashSalt);
         case 6: return ZSTD_hash6PtrS(p, hBits, hashSalt);
         case 7: return ZSTD_hash7PtrS(p, hBits, hashSalt);

lib/compress/zstd_lazy.c

@@ -906,6 +906,7 @@ FORCE_INLINE_TEMPLATE void ZSTD_row_update_internalImpl(ZSTD_matchState_t* ms,
         assert(hash == ZSTD_hashPtrSalted(base + updateStartIdx, hashLog + ZSTD_ROW_HASH_TAG_BITS, mls, ms->hashSalt));
         ((BYTE*)tagRow)[pos + ZSTD_ROW_HASH_TAG_OFFSET] = hash & ZSTD_ROW_HASH_TAG_MASK;
         row[pos] = updateStartIdx;
+        ms->hashSaltEntropy += hash;
     }
 }