Re: [PATCH 10/10] timegm: add portable implementation (Solaris support)

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+       Mon,  5 Nov 2012 14:09:33 +0200 (EET)\r
+From: Tomi Ollila <tomi.ollila@iki.fi>\r
+To: Blake Jones <blakej@foo.net>, Jani Nikula <jani@nikula.org>\r
+Subject: Re: [PATCH 10/10] timegm: add portable implementation (Solaris\r
+       support)\r
+In-Reply-To: <12349.1352043650@foo.net>\r
+References: <12349.1352043650@foo.net>\r
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+Date: Mon, 05 Nov 2012 14:09:33 +0200\r
+Message-ID: <m2txt4jloi.fsf@guru.guru-group.fi>\r
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+\r
+--=-=-=\r
+Content-Type: text/plain\r
+\r
+On Sun, Nov 04 2012, Blake Jones wrote:\r
+\r
+> Hi Jani,\r
+>\r
+>> I'd prefer to use timegm() where available, and the suggested\r
+>> alternative [1] elsewhere.\r
+>> \r
+>> [1] http://www.kernel.org/doc/man-pages/online/pages/man3/timegm.3.html\r
+>\r
+> I considered this alternative, but decided against it because it's\r
+> completely MT-unsafe.  I don't know whether libnotmuch itself is\r
+> MT-safe, but a process which called this routine in one thread would\r
+> temporarily throw off any timezone-related work that any other threads\r
+> were doing, even if they weren't using libnotmuch.\r
+\r
+Yet another idea for an alternative. Compile by entering 'sh xtimegm.c'\r
+and then run ./xtimegm\r
+\r
+Simple cases seems to work. Dst change may (or then may not) give one\r
+hour difference to the expected. The test "coverage" could be easily\r
+expanded to that ;)\r
+\r
+Hmm, I also found this:\r
+http://lists.gnu.org/archive/html/bug-gnulib/2003-09/msg00004.html\r
+which does 2 mktime's and one gmtime_r (without allocating tg!)...\r
+Pick any of these 3 -- or something different (e.g. less NIH if there is)\r
+\r
+> Blake\r
+\r
+\r
+Tomi\r
+\r
+\r
+--=-=-=\r
+Content-Type: text/plain; charset=utf-8\r
+Content-Disposition: inline; filename=xtimegm.c\r
+Content-Transfer-Encoding: quoted-printable\r
+Content-Description: yet another attempt for timegm() implementation\r
+\r
+#if 0 /* -*- mode: c; c-file-style: "stroustrup"; tab-width: 8; -*-\r
+ set -eu; trg=3D`basename "$0" .c`; rm -f "$trg"\r
+ WARN=3D"-Wall -Wno-long-long -Wstrict-prototypes -pedantic"\r
+ WARN=3D"$WARN -Wcast-align -Wpointer-arith " # -Wfloat-equal #-Werror\r
+ WARN=3D"$WARN -W -Wwrite-strings -Wcast-qual -Wshadow" # -Wconversion\r
+ case ${1-} in '') set x -O2; shift; esac\r
+ #case ${1-} in '') set x -ggdb; shift; esac\r
+ set -x; exec ${CC:-gcc} -std=3Dc99 $WARN "$@" -o "$trg" "$0"\r
+ exit $?\r
+ */\r
+#endif\r
+/*\r
+ * $ xtimegm.c $\r
+ *\r
+ * Author: Tomi Ollila -- too =C3=A4t iki piste fi\r
+ *\r
+ * Created: Mon 05 Nov 2012 07:54:35 EET too\r
+ * Last modified: Mon 05 Nov 2012 08:27:52 EET too\r
+ *\r
+ * Public domain.\r
+ */\r
+\r
+#define _POSIX_SOURCE\r
+\r
+#include <time.h>\r
+\r
+time_t xtimegm(struct tm * atm)\r
+{\r
+    struct tm ltm;\r
+    time_t t =3D mktime(atm);\r
+    int sd;\r
+    int dd;\r
+\r
+    (void)gmtime_r(&t, &ltm);\r
+\r
+    sd =3D (atm->tm_hour - ltm.tm_hour) * 3600 + (atm->tm_min - ltm.tm_min)=\r
+ * 60\r
+       + (atm->tm_sec - ltm.tm_sec);\r
+\r
+    dd =3D (atm->tm_mday - ltm.tm_mday);\r
+\r
+    if (dd =3D=3D 0)\r
+       ;\r
+    else if (dd =3D=3D -1) sd -=3D 86400;  /* e.g. 3, 2 */\r
+    else if (dd =3D=3D 1)  sd +=3D 86400;  /* e.g. 2, 3 */\r
+    else if (dd > 1)   sd -=3D 86400;  /* e.g. 1, 31 */\r
+    else /* dd < 1 */  sd +=3D 86400;  /* e.g. 31, 1 */\r
+\r
+    printf("sd: %d\n", sd); // test line.\r
+\r
+    return t + sd;\r
+}\r
+\r
+#include <stdio.h>\r
+void test(int hour, int mday)\r
+{\r
+    struct tm mtm;\r
+    time_t t;\r
+    struct tm * otm;\r
+\r
+    mtm.tm_sec =3D 0;\r
+    mtm.tm_min =3D 0;\r
+    mtm.tm_hour =3D hour;\r
+\r
+    mtm.tm_mday =3D mday;\r
+    mtm.tm_mon =3D 11;\r
+    mtm.tm_year =3D 100;\r
+    mtm.tm_isdst =3D -1;\r
+\r
+    t =3D xtimegm(&mtm);\r
+    otm =3D gmtime(&t);\r
+\r
+    printf("%2d %02d:%02d:%02d\n", otm->tm_mday,\r
+          otm->tm_hour, otm->tm_min, otm->tm_sec);\r
+}\r
+\r
+void tests(const char * tz)\r
+{\r
+    printf("TZ: %s\n", tz);\r
+    setenv("TZ", tz, 1);\r
+    tzset();\r
+    test(23, 30);\r
+    test(23, 31);\r
+    test(23, 1);\r
+    test(23, 2);\r
+    printf("--\n");\r
+    test(1, 30);\r
+    test(1, 31);\r
+    test(1, 1);\r
+    test(1, 2);\r
+\r
+}\r
+\r
+int main(int argc, char * argv[])\r
+{\r
+    // ls /usr/share/zoneinfo...\r
+    tests("EET");\r
+    tests("MST");\r
+    tests("HST");\r
+    tests("NZ");\r
+\r
+    return 0;\r
+}\r
+\r
+--=-=-=--\r