From 6f8089482391e999fa772e7b8579ff5f89ec79c1 Mon Sep 17 00:00:00 2001
From: Emmanuel Marty <emmanuel@fgl.com>
Date: Tue, 25 Jun 2019 13:16:25 +0200
Subject: [PATCH] Fix matchfinder limitation

---
 src/lz4ultra.c       |  2 +-
 src/matchfinder.c    | 20 +++++++-------------
 src/shrink_context.h |  2 ++
 3 files changed, 10 insertions(+), 14 deletions(-)

diff --git a/src/lz4ultra.c b/src/lz4ultra.c
index a737f02..4a5c52f 100755
--- a/src/lz4ultra.c
+++ b/src/lz4ultra.c
@@ -50,7 +50,7 @@
 #define OPT_INDEP_BLOCKS   8
 #define OPT_LEGACY_FRAMES  16
 
-#define TOOL_VERSION "1.2.1"
+#define TOOL_VERSION "1.2.2"
 
 /*---------------------------------------------------------------------------*/
 
diff --git a/src/matchfinder.c b/src/matchfinder.c
index 99e24b2..45397de 100644
--- a/src/matchfinder.c
+++ b/src/matchfinder.c
@@ -197,33 +197,27 @@ static int lz4ultra_find_matches_at(lz4ultra_compressor *pCompressor, const int
    /* Ascend until we reach a visited interval, the root, or a child of the
     * root.  Link unvisited intervals to the current suffix as we go.  */
    while ((super_ref = intervals[ref & POS_MASK]) & LCP_MASK) {
-      intervals[ref & POS_MASK] = nOffset;
+      intervals[ref & POS_MASK] = nOffset | VISITED_FLAG;
       ref = super_ref;
    }
 
    if (super_ref == 0) {
       /* In this case, the current interval may be any of:
        * (1) the root;
-       * (2) an unvisited child of the root;
-       * (3) an interval last visited by suffix 0
-       *
-       * We could avoid the ambiguity with (3) by using an lcp
-       * placeholder value other than 0 to represent "visited", but
-       * it's fastest to use 0.  So we just don't allow matches with
-       * position 0.  */
+       * (2) an unvisited child of the root */
 
       if (ref != 0)  /* Not the root?  */
-         intervals[ref & POS_MASK] = nOffset;
+         intervals[ref & POS_MASK] = nOffset | VISITED_FLAG;
       return 0;
    }
 
    /* Ascend indirectly via pos_data[] links.  */
-   match_pos = super_ref;
+   match_pos = super_ref & EXCL_VISITED_MASK;
    matchptr = pMatches;
    for (;;) {
       while ((super_ref = pos_data[match_pos]) > ref)
-         match_pos = intervals[super_ref & POS_MASK];
-      intervals[ref & POS_MASK] = nOffset;
+         match_pos = intervals[super_ref & POS_MASK] & EXCL_VISITED_MASK;
+      intervals[ref & POS_MASK] = nOffset | VISITED_FLAG;
       pos_data[match_pos] = (unsigned long long)ref;
 
       if ((matchptr - pMatches) < nMaxMatches) {
@@ -239,7 +233,7 @@ static int lz4ultra_find_matches_at(lz4ultra_compressor *pCompressor, const int
       if (super_ref == 0)
          break;
       ref = super_ref;
-      match_pos = intervals[ref & POS_MASK];
+      match_pos = intervals[ref & POS_MASK] & EXCL_VISITED_MASK;
    }
 
    return (int)(matchptr - pMatches);
diff --git a/src/shrink_context.h b/src/shrink_context.h
index cbe029f..1c12534 100644
--- a/src/shrink_context.h
+++ b/src/shrink_context.h
@@ -40,6 +40,8 @@
 #define LCP_SHIFT (39-LCP_BITS)
 #define LCP_MASK (((1ULL<<LCP_BITS) - 1) << LCP_SHIFT)
 #define POS_MASK ((1ULL<<LCP_SHIFT) - 1)
+#define VISITED_FLAG 0x8000000000ULL
+#define EXCL_VISITED_MASK  0x7fffffffffULL
 
 #define NMATCHES_PER_OFFSET 8
 #define MATCHES_PER_OFFSET_SHIFT 3