timegm: add portable implementation (Solaris support)

The timegm(3) function is a non-standard extension to libc which is
available in GNU libc and on some BSDs.  Although SunOS had this
function in its libc, Solaris (unfortunately) removed it.  This patch
implements a very simple version of timegm() which is good enough for
parse-time-string.c.

Signed-off-by: Vladimir Marek <vlmarek@volny.cz>

compat/Makefile.local

@@ -17,4 +17,8 @@ ifneq ($(HAVE_STRSEP),1)
 notmuch_compat_srcs += $(dir)/strsep.c
 endif
 
+ifneq ($(HAVE_TIMEGM),1)
+notmuch_compat_srcs += $(dir)/timegm.c
+endif
+
 SRCS := $(SRCS) $(notmuch_compat_srcs)

compat/compat.h

@@ -57,6 +57,11 @@ char* strcasestr(const char *haystack, const char *needle);
 char *strsep(char **stringp, const char *delim);
 #endif /* !HAVE_STRSEP */
 
+#if !HAVE_TIMEGM
+#include <time.h>
+time_t timegm (struct tm *tm);
+#endif /* !HAVE_TIMEGM */
+
 /* Silence gcc warnings about unused results.  These warnings exist
  * for a reason; any use of this needs to be justified. */
 #ifdef __GNUC__

compat/have_timegm.c

@@ -0,0 +1,7 @@
+#include <time.h>
+#include "compat.h"
+
+int main()
+{
+    return (int) timegm((struct tm *)0);
+}

compat/timegm.c

@@ -0,0 +1,56 @@
+/* timegm.c --- Implementation of replacement timegm function.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License as
+   published by the Free Software Foundation; either version 3, or (at
+   your option) any later version.
+
+   This program is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+   02110-1301, USA.  */
+
+/* Copyright 2013 Blake Jones. */
+
+#include <time.h>
+#include "compat.h"
+
+static int
+leapyear (int year)
+{
+    return ((year % 4) == 0 && ((year % 100) != 0 || (year % 400) == 0));
+}
+
+/*
+ * This is a simple implementation of timegm() which does what is needed
+ * by create_output() -- just turns the "struct tm" into a GMT time_t.
+ * It does not normalize any of the fields of the "struct tm", nor does
+ * it set tm_wday or tm_yday.
+ */
+time_t
+timegm (struct tm *tm)
+{
+    int	monthlen[2][12] = {
+	{ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 },
+	{ 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 },
+    };
+    int	year, month, days;
+
+    days = 365 * (tm->tm_year - 70);
+    for (year = 70; year < tm->tm_year; year++) {
+	if (leapyear(1900 + year)) {
+	    days++;
+	}
+    }
+    for (month = 0; month < tm->tm_mon; month++) {
+	days += monthlen[leapyear(1900 + year)][month];
+    }
+    days += tm->tm_mday - 1;
+
+    return ((((days * 24) + tm->tm_hour) * 60 + tm->tm_min) * 60 + tm->tm_sec);
+}

configure

@@ -530,6 +530,17 @@ else
 fi
 rm -f compat/have_strsep
 
+printf "Checking for timegm... "
+if ${CC} -o compat/have_timegm "$srcdir"/compat/have_timegm.c > /dev/null 2>&1
+then
+    printf "Yes.\n"
+    have_timegm="1"
+else
+    printf "No (will use our own instead).\n"
+    have_timegm="0"
+fi
+rm -f compat/have_timegm
+
 printf "Checking for standard version of getpwuid_r... "
 if ${CC} -o compat/check_getpwuid "$srcdir"/compat/check_getpwuid.c > /dev/null 2>&1
 then

parse-time-string/parse-time-string.c

@@ -32,6 +32,7 @@
 #include <sys/time.h>
 #include <sys/types.h>
 
+#include "compat.h"
 #include "parse-time-string.h"
 
 /*