Fix Hash-Table Sizing of Small Inputs

For inputs smaller than `1 << ZSTD_WINDOWLOG_MIN` bytes, the pre-existing
code in `ZSTD_adjustCParams_internal()` temporarily calculated an illegally
small window log for the purposes of adjusting the hash- and chain-table
sizes, before fixing that bad window log to comply with the minimums. The new
code clamped the window log earlier and therefore didn't shrink the tables as
much. This commit fixes that to mirror the pre-existing behavior.

This resolves the remaining regression test differences.

Author: felixhandte

lib/compress/zstd_compress.c

@@ -1490,7 +1490,7 @@ static void ZSTD_dictAndWindowLog(ZSTD_CParams* cParams, U64 srcSize, U64 dictSi
         if (windowSize >= dictSize + srcSize) {
             /* Window size large enough already */
         } else {
-            ZSTD_setMinimalWindowLogAndFrac(cParams, (U32)dictAndWindowSize);
+            ZSTD_setMinimalWindowLogAndFrac(cParams, (U32)dictAndWindowSize, ZSTD_WINDOWLOG_MIN);
         }
     }
 }
@@ -1600,7 +1600,8 @@ ZSTD_adjustCParams_internal(ZSTD_CParams cPar,
             if (ZSTD_windowSize(&cPar) > (1u << (ZSTD_highbit32(tSize - 1) + 1)))
 #endif
             {
-                ZSTD_setMinimalWindowLogAndFrac(&cPar, tSize);
+                const U32 tmpMinWindowLog = ZSTD_HASHLOG_MIN < ZSTD_WINDOWLOG_MIN ? ZSTD_HASHLOG_MIN : ZSTD_WINDOWLOG_MIN;
+                ZSTD_setMinimalWindowLogAndFrac(&cPar, tSize, tmpMinWindowLog);
             }
         }
     }
@@ -6000,7 +6001,7 @@ static size_t ZSTD_compressBegin_usingCDict_internal(
     if (pledgedSrcSize != ZSTD_CONTENTSIZE_UNKNOWN) {
         U32 const limitedSrcSize = (U32)MIN(pledgedSrcSize, 1U << 19);
         if (limitedSrcSize > 1 && ZSTD_windowSize(&cctxParams.cParams) < limitedSrcSize) {
-            ZSTD_setMinimalWindowLogAndFrac(&cctxParams.cParams, limitedSrcSize);
+            ZSTD_setMinimalWindowLogAndFrac(&cctxParams.cParams, limitedSrcSize, ZSTD_WINDOWLOG_MIN);
         }
     }
     return ZSTD_compressBegin_internal(cctx,

lib/compress/zstd_compress_internal.h

@@ -1152,11 +1152,11 @@ MEM_STATIC int ZSTD_windowLogAndFracAreMinimal(ZSTD_CParams* cParams, const U32
  * Calculates the minimum legal window log and fraction that contain the
  * provided source size.
  */
-MEM_STATIC void ZSTD_setMinimalWindowLogAndFrac(ZSTD_CParams* cParams, const U32 srcSize) {
-    const U32 minSize = 1u << ZSTD_WINDOWLOG_ABSOLUTEMIN;
+MEM_STATIC void ZSTD_setMinimalWindowLogAndFrac(ZSTD_CParams* cParams, const U32 srcSize, const U32 minWindowLog) {
+    const U32 minSize = 1u << minWindowLog;
 #if ZSTD_WINDOW_ALLOW_PICKING_FRACTIONAL_SIZES
     if (srcSize < minSize) {
-        cParams->windowLog = ZSTD_WINDOWLOG_ABSOLUTEMIN;
+        cParams->windowLog = minWindowLog;
         cParams->windowFrac = 0;
     } else {
         const U32 srcSizeMinusOne = srcSize - 1;
@@ -1169,7 +1169,7 @@ MEM_STATIC void ZSTD_setMinimalWindowLogAndFrac(ZSTD_CParams* cParams, const U32
     }
 #else
     if (srcSize < minSize) {
-        cParams->windowLog = ZSTD_WINDOWLOG_ABSOLUTEMIN;
+        cParams->windowLog = minWindowLog;
         cParams->windowFrac = 0;
     } else {
         cParams->windowLog = ZSTD_highbit32(srcSize - 1) + 1;