On Wed, Feb 10, 2010 at 03:28:17PM +0000, Joseph Jezak wrote:
> This patch fixes commit dcb54fafb128ab41772ae217afc6a7612e2cc446 which is broken
> on big endian, 64 bit machines. The data is stored in the upper 4 bytes of the
> pointer on these machines, but the code was reading the lower 4 bytes. This
> resulted in the first day of the week being reported incorrectly.
Good catch. Thanks!
> {
> - int wfd = (int)(intptr_t) nl_langinfo(_NL_TIME_WEEK_1STDAY);
> + char *wfd_ptr = nl_langinfo(_NL_TIME_WEEK_1STDAY);
> + int *wfd_int_ptr = (int *)(&wfd_ptr);
At first glance it seems usable, but this cast is against strict-aliasing
rules (try gcc -Wall).
I have reverted the commit dcb54fafb128ab41772ae217afc6a7612e2cc446,
it seems that the original solution (based on union) is portable. See
the patch below.
Karel
>From aebb9522b78ded9cc00475b2dfc98813a0cbf202 Mon Sep 17 00:00:00 2001
From: Karel Zak <kzak@xxxxxxxxxx>
Date: Thu, 11 Feb 2010 16:29:05 +0100
Subject: [PATCH] cal: fix first day of the week calculation on BE systems
This reverts commit dcb54fafb128ab41772ae217afc6a7612e2cc446,
"cal: remove gcc-ism from nl_langinfo() call".
The code:
int wfd = (int)(intptr_t) nl_langinfo(_NL_TIME_WEEK_1STDAY);
does not work on big-endian machines. The original solution based on
union is better.
Note that the "type punning" is not gcc-ism any more, it's allowed
by C99 (6.5.2.3).
Reported-by: Joseph Jezak <josejx@xxxxxxxxxx>
Signed-off-by: Karel Zak <kzak@xxxxxxxxxx>
---
misc-utils/cal.c | 6 +++++-
1 files changed, 5 insertions(+), 1 deletions(-)
diff --git a/misc-utils/cal.c b/misc-utils/cal.c
index 5444cea..5eb14b5 100644
--- a/misc-utils/cal.c
+++ b/misc-utils/cal.c
@@ -312,7 +312,11 @@ main(int argc, char **argv) {
POSIX: 19971201 + 7 -1 = 0
*/
{
- int wfd = (int)(intptr_t) nl_langinfo(_NL_TIME_WEEK_1STDAY);
+ int wfd;
+ union { unsigned int word; char *string; } val;
+ val.string = nl_langinfo(_NL_TIME_WEEK_1STDAY);
+
+ wfd = val.word;
wfd = day_in_week(wfd % 100, (wfd / 100) % 100, wfd / (100 * 100));
weekstart = (wfd + *nl_langinfo(_NL_TIME_FIRST_WEEKDAY) - 1) % 7;
}
--
1.6.6
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