From 19fe725976fddaf4b36ce92645099d9187a2674e Mon Sep 17 00:00:00 2001
From: Gary Langshaw <gary.langshaw@gmail.com>
Date: Wed, 7 Aug 2024 22:35:22 +0100
Subject: [PATCH] database.c: avoid undefined behaviour in FixDayDow()

This issue was flagged by clang-static-analyser:

mask |= 1 << (i - 1) will result in undefined behaviour when i == 0
as the lshift operand will be negative.

As cl_Days[] only uses indices 1..31 we can avoid the potential issue
by starting the iteration at index 1.
---
 database.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/database.c b/database.c
index ba71b93..2de2693 100644
--- a/database.c
+++ b/database.c
@@ -852,7 +852,7 @@ FixDayDow(CronLine *line)
 		}
 	}
 
-	for (i = 0; i < arysize(line->cl_Days); ++i) {
+	for (i = 1; i < arysize(line->cl_Days); ++i) {
 		if (line->cl_Days[i] == 0) {
 			/* '*' was NOT specified in the Date field on this CronLine */
 			DomStar = 0;
@@ -865,7 +865,7 @@ FixDayDow(CronLine *line)
 		return;
 
 	/* Set individual bits within the DoW mask... */
-	for (i = 0; i < arysize(line->cl_Days); ++i) {
+	for (i = 1; i < arysize(line->cl_Days); ++i) {
 		if (line->cl_Days[i]) {
 			if (i < 6)
 				mask |= 1 << (i - 1);