Fix matchfinder limitation

emmanuel-marty · Jun 25, 2019 · 6f80894 · 6f80894
1 parent efdeab3
commit 6f80894
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Showing 3 changed files with 10 additions and 14 deletions.
diff --git 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
@@ -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
@@ -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