>From cebe2057d2970043db7e5efd839d9e663eaf0309 Mon Sep 17 00:00:00 2001
From: Szabolcs Nagy <nsz@port70.net>
Date: Sun, 27 Sep 2026 15:12:37 +0000
Subject: [PATCH 19/25] regex: refactor tag list merging

factor out "concatenate tags with duplicate removal" into merge_nodup
to optimize it later and apply elsewhere.
---
 src/regex/regcomp.c | 43 +++++++++++++++++--------------------------
 1 file changed, 17 insertions(+), 26 deletions(-)

diff --git a/src/regex/regcomp.c b/src/regex/regcomp.c
index be5fa595..ed35ac72 100644
--- a/src/regex/regcomp.c
+++ b/src/regex/regcomp.c
@@ -2013,6 +2013,20 @@ tre_expand_ast(tre_mem_t mem, tre_stack_t *stack, tre_ast_node_t *ast,
   return status;
 }
 
+/* merge s1 and s2 with no dups into out with no dups, returns length of out. */
+static int merge_nodup(int *out, int *s1, int n1, int *s2, int n2)
+{
+	int i=0, j=0, n=n1, v;
+	for (i=0; i<n1; i++) out[i] = s1[i];
+	for (j=0; j<n2; j++) {
+		v = s2[j];
+		for (i=0; i<n1 && v!=out[i]; i++);
+		if (i==n1)
+			out[n++] = v;
+	}
+	return n;
+}
+
 static tre_pos_and_tags_t *
 tre_set_empty(tre_mem_t mem)
 {
@@ -2481,7 +2495,7 @@ tre_make_trans(tre_pos_and_tags_t *p1, tre_pos_and_tags_t *p2,
 {
   tre_pos_and_tags_t *orig_p2 = p2;
   tre_tnfa_transition_t *trans;
-  int i, j, k, l, dup, prev_p2_pos;
+  int i, j, prev_p2_pos;
 
   if (transitions != NULL)
     while (p1->position >= 0)
@@ -2577,31 +2591,8 @@ tre_make_trans(tre_pos_and_tags_t *p1, tre_pos_and_tags_t *p2,
 		trans->tags = xmalloc(sizeof(*trans->tags) * (i + j + 1));
 		if (!trans->tags)
 		  return REG_ESPACE;
-		i = 0;
-		if (p1->tags != NULL)
-		  while(p1->tags[i] >= 0)
-		    {
-		      trans->tags[i] = p1->tags[i];
-		      i++;
-		    }
-		l = i;
-		j = 0;
-		if (p2->tags != NULL)
-		  while (p2->tags[j] >= 0)
-		    {
-		      /* Don't add duplicates. */
-		      dup = 0;
-		      for (k = 0; k < i; k++)
-			if (trans->tags[k] == p2->tags[j])
-			  {
-			    dup = 1;
-			    break;
-			  }
-		      if (!dup)
-			trans->tags[l++] = p2->tags[j];
-		      j++;
-		    }
-		trans->tags[l] = -1;
+		i = merge_nodup(trans->tags, p1->tags, i, p2->tags, j);
+		trans->tags[i] = -1;
 	      }
 
 	    p2++;
-- 
2.52.0