[PATCH 047/112] string: reduce strjoin runtime, drop trailing separator

[Ahmad Fatoum]

The implementation of strjoin is a bit suboptimal. The destination
string is traversed from the beginning due to strcat and we have a
left-over separator at the end, while it should only be in-between.

Fix this.

Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
Originally posted at: https://lore.barebox.org/barebox/20221027073334.GS6702@pengutronix.de/

Changes:
  - remove if statemnt in loop (Sascha)
Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
 lib/string.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/lib/string.c b/lib/string.c
index d8e5edd40648..695e50bc8fc1 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -1005,7 +1005,7 @@ char *strjoin(const char *separator, char **arr, size_t arrlen)
 {
 	size_t separatorlen;
 	int len = 1; /* '\0' */
-	char *buf;
+	char *buf, *p;
 	int i;
 
 	separatorlen = strlen(separator);
@@ -1013,13 +1013,18 @@ char *strjoin(const char *separator, char **arr, size_t arrlen)
 	for (i = 0; i < arrlen; i++)
 		len += strlen(arr[i]) + separatorlen;
 
-	buf = xzalloc(len);
+	if (!arrlen)
+		return xzalloc(1);
 
-	for (i = 0; i < arrlen; i++) {
-		strcat(buf, arr[i]);
-		strcat(buf, separator);
+	p = buf = xmalloc(len);
+
+	for (i = 0; i < arrlen - 1; i++) {
+		p = stpcpy(p, arr[i]);
+		p = mempcpy(p, separator, separatorlen);
 	}
 
+	stpcpy(p, arr[i]);
+
 	return buf;
 }
 EXPORT_SYMBOL(strjoin);
-- 
2.39.2