From a1633e09a761b9135a0a7084d2489d359a004e5a Mon Sep 17 00:00:00 2001
From: Peter Stephenson <pws@zsh.org>
Date: Wed, 9 Nov 2016 11:54:57 +0000
Subject: 39886 based on 39877: Optimise arrdup to arrdup_max.

Only duplicate as much of the array as is needed.
---
 Src/params.c | 24 +++++++++++++++++-------
 Src/utils.c  | 25 +++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 7 deletions(-)

(limited to 'Src')

diff --git a/Src/params.c b/Src/params.c
index 3f0179267..772345bd1 100644
--- a/Src/params.c
+++ b/Src/params.c
@@ -2294,14 +2294,24 @@ getarrvalue(Value v)
 	v->start += arrlen(s);
     if (v->end < 0)
 	v->end += arrlen(s) + 1;
-    if (arrlen_lt(s, v->start) || v->start < 0)
+
+    /* Null if 1) array too short, 2) index still negative */
+    if (arrlen_lt(s, v->start) || v->start < 0) {
 	s = arrdup(nular);
-    else
-	s = arrdup(s + v->start);
-    if (v->end <= v->start)
-	s[0] = NULL;
-    else if (arrlen_ge(s, v->end - v->start))
-	s[v->end - v->start] = NULL;
+    } else if (v->end <= v->start) {
+        s = arrdup_max(s, 1);
+        s[0] = NULL;
+    } else {
+        /* Copy to a point before the end of the source array:
+         * arrdup_max will copy at most v->end - v->start elements,
+         * starting from v->start element. Original code said:
+	 *  s[v->end - v->start] = NULL
+         * which means that there are exactly the same number of
+         * elements as the value of the above *0-based* index.
+         */
+	s = arrdup_max(s + v->start, v->end - v->start);
+    }
+
     return s;
 }
 
diff --git a/Src/utils.c b/Src/utils.c
index 93e757ce8..3d535b85c 100644
--- a/Src/utils.c
+++ b/Src/utils.c
@@ -4229,6 +4229,31 @@ arrdup(char **s)
     return y;
 }
 
+/* Duplicate at most max elements of the array s with heap memory */
+
+/**/
+mod_export char **
+arrdup_max(char **s, unsigned max)
+{
+    char **x, **y, **send;
+    int len;
+
+    len = arrlen(s);
+
+    /* Limit has sense only if not equal to len */
+    if (max > len)
+        max = len;
+
+    y = x = (char **) zhalloc(sizeof(char *) * (max + 1));
+
+    send = s + max;
+    while (s < send)
+	*x++ = dupstring(*s++);
+    *x = NULL;
+
+    return y;
+}
+
 /**/
 mod_export char **
 zarrdup(char **s)
-- 
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