From 298d24fa573842c7cc0c3530869817bc9ebe36f8 Mon Sep 17 00:00:00 2001
From: "W. Felix Handte" <w@felixhandte.com>
Date: Mon, 21 May 2018 20:12:11 -0400
Subject: [PATCH] Make loadedDictEnd an Index, not the Dict Len

---
 lib/compress/zstd_compress.c          | 4 +++-
 lib/compress/zstd_compress_internal.h | 6 ++++++
 lib/compress/zstd_fast.c              | 2 +-
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/lib/compress/zstd_compress.c b/lib/compress/zstd_compress.c
index e49046fc..105cea44 100644
--- a/lib/compress/zstd_compress.c
+++ b/lib/compress/zstd_compress.c
@@ -1209,6 +1209,8 @@ static size_t ZSTD_resetCCtx_usingCDict(ZSTD_CCtx* cctx,
      * in-place. We decide here which strategy to use. */
     const int attachDict = ( pledgedSrcSize <= 8 KB
                           || pledgedSrcSize == ZSTD_CONTENTSIZE_UNKNOWN )
+                        && !params.forceWindow /* dictMatchState isn't correctly
+                                                * handled in _enforceMaxDist */
                         && cdict->cParams.strategy == ZSTD_fast
                         && ZSTD_equivalentCParams(cctx->appliedParams.cParams,
                                                   cdict->cParams);
@@ -1244,7 +1246,7 @@ static size_t ZSTD_resetCCtx_usingCDict(ZSTD_CCtx* cctx,
                     cctx->blockState.matchState.window.base + cdictLen;
                 ZSTD_window_clear(&cctx->blockState.matchState.window);
             }
-            cctx->blockState.matchState.loadedDictEnd = params.forceWindow ? 0 : cdictLen;
+            cctx->blockState.matchState.loadedDictEnd = cctx->blockState.matchState.window.dictLimit;
         }
     } else {
         DEBUGLOG(4, "copying dictionary into context");
diff --git a/lib/compress/zstd_compress_internal.h b/lib/compress/zstd_compress_internal.h
index a61fc374..a7666d5c 100644
--- a/lib/compress/zstd_compress_internal.h
+++ b/lib/compress/zstd_compress_internal.h
@@ -594,14 +594,20 @@ MEM_STATIC U32 ZSTD_window_correctOverflow(ZSTD_window_t* window, U32 cycleLog,
  * ZSTD_window_enforceMaxDist():
  * Updates lowLimit so that:
  *    (srcEnd - base) - lowLimit == maxDist + loadedDictEnd
+ *
  * This allows a simple check that index >= lowLimit to see if index is valid.
  * This must be called before a block compression call, with srcEnd as the block
  * source end.
+ *
  * If loadedDictEndPtr is not NULL, we set it to zero once we update lowLimit.
  * This is because dictionaries are allowed to be referenced as long as the last
  * byte of the dictionary is in the window, but once they are out of range,
  * they cannot be referenced. If loadedDictEndPtr is NULL, we use
  * loadedDictEnd == 0.
+ *
+ * In normal dict mode, the dict is between lowLimit and dictLimit. In
+ * dictMatchState mode, lowLimit and dictLimit are the same, and the dictionary
+ * is below them. forceWindow and dictMatchState are therefore incompatible.
  */
 MEM_STATIC void ZSTD_window_enforceMaxDist(ZSTD_window_t* window,
                                            void const* srcEnd, U32 maxDist,
diff --git a/lib/compress/zstd_fast.c b/lib/compress/zstd_fast.c
index 3bac2bdd..bf962a17 100644
--- a/lib/compress/zstd_fast.c
+++ b/lib/compress/zstd_fast.c
@@ -72,7 +72,7 @@ size_t ZSTD_compressBlock_fast_generic(
     const BYTE* const dictEnd      = dictMode == ZSTD_dictMatchState ?
                                      dms->window.nextSrc : NULL;
     const U32 dictIndexDelta       = dictMode == ZSTD_dictMatchState ?
-                                     prefixLowestIndex - (U32)(dictEnd - dictBase) :
+                                     ms->loadedDictEnd - (U32)(dictEnd - dictBase) :
                                      0;
     const U32 dictAndPrefixLength  = (U32)(ip - prefixLowest + dictEnd - dictLowest);