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Date: Wed, 25 Jul 2018 12:11:42 +0200
From: Rafał Miłecki <zajec5@...il.com>
To: musl@...ts.openwall.com
Cc: Rafał Miłecki <rafal@...ecki.pl>
Subject: [PATCH] strftime: fix %z sign for small negative time zone offsets

From: Rafał Miłecki <rafal@...ecki.pl>

Using + printf flag for printing plus/minus sign isn't reliable for
negative offsets greater than -3600. In such cases the first two digits
are zero but offset still should be printed with a leading minus char.

Existing implementation results in code:
	struct tm tm = { .tm_gmtoff = -1800, };
	char buf[255];
	strftime(buf, sizeof(buf), "%z", &tm);
	puts(buf);
printing +0030 instead of -0030.

This patch fixes it by handling sign character manually and checking the
__tm_gmtoff value (instead of __tm_gmtoff / 3600).

Signed-off-by: Rafał Miłecki <rafal@...ecki.pl>
---
 src/time/strftime.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/time/strftime.c b/src/time/strftime.c
index 0a256970..6716ad4b 100644
--- a/src/time/strftime.c
+++ b/src/time/strftime.c
@@ -181,7 +181,8 @@ const char *__strftime_fmt_1(char (*s)[100], size_t *l, int f, const struct tm *
 			*l = 0;
 			return "";
 		}
-		*l = snprintf(*s, sizeof *s, "%+.2ld%.2d",
+		*l = snprintf(*s, sizeof *s, "%c%.2ld%.2d",
+			tm->__tm_gmtoff >= 0 ? '+' : '-',
 			(tm->__tm_gmtoff)/3600,
 			abs(tm->__tm_gmtoff%3600)/60);
 		return *s;
-- 
2.13.7

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