From b500c5282e61027b797d3fd39e7d4ab1ab084adf Mon Sep 17 00:00:00 2001
From: Yann Collet <cyan@fb.com>
Date: Thu, 7 Sep 2017 12:48:24 -0700
Subject: fix #397 : decompression failed when using a combination of extDict +
 low memory address

Reported and fixed by @jscheid

Note : we are missing a test case to include it in the CI
---
 NEWS      | 1 +
 lib/lz4.c | 3 +--
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/NEWS b/NEWS
index 57338f7..ff20e7e 100644
--- a/NEWS
+++ b/NEWS
@@ -1,4 +1,5 @@
 v1.8.1
+fix : decompression failed when using a combination of extDict + low memory address (#397), reported and fixed by Julian Scheid (@jscheid)
 install: fix : correct man page directory (#387), reported by Stuart Cardall (@itoffshore)
 build  : `make` and `make test` compatible with `-jX`, reported by @mwgamera
 
diff --git a/lib/lz4.c b/lib/lz4.c
index f361b22..0960c97 100644
--- a/lib/lz4.c
+++ b/lib/lz4.c
@@ -1127,7 +1127,6 @@ LZ4_FORCE_INLINE int LZ4_decompress_generic(
     BYTE* const oend = op + outputSize;
     BYTE* cpy;
     BYTE* oexit = op + targetOutputSize;
-    const BYTE* const lowLimit = lowPrefix - dictSize;
 
     const BYTE* const dictEnd = (const BYTE*)dictStart + dictSize;
     const unsigned dec32table[] = {0, 1, 2, 1, 4, 4, 4, 4};
@@ -1183,7 +1182,7 @@ LZ4_FORCE_INLINE int LZ4_decompress_generic(
         /* get offset */
         offset = LZ4_readLE16(ip); ip+=2;
         match = op - offset;
-        if ((checkOffset) && (unlikely(match < lowLimit))) goto _output_error;   /* Error : offset outside buffers */
+        if ((checkOffset) && (unlikely(match + dictSize < lowPrefix))) goto _output_error;   /* Error : offset outside buffers */
         LZ4_write32(op, (U32)offset);   /* costs ~1%; silence an msan warning when offset==0 */
 
         /* get matchlength */
-- 
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