[PATCH] Refactor mktime and add the POSIX function timegm

["R. Diez" <rdiezmail-newlib@yahoo.de>]

I have manually reconstructed the patch from Andrew Russell posted here:

https://sourceware.org/legacy-ml/newlib/2018/msg00824.html

Is the new implementation of __is_leap_year() right? I would rather keep the old ISLEAP implementation.

R. Diez (1):
  Refactor mktime and add the POSIX function timegm

 newlib/libc/include/time.h   |  3 ++
 newlib/libc/saber            |  1 +
 newlib/libc/time/Makefile.am |  2 +
 newlib/libc/time/Makefile.in |  9 +++++
 newlib/libc/time/local.h     |  2 +
 newlib/libc/time/mktime.c    | 78 +++++++++++++++++++++++++-----------
 newlib/libc/time/timegm.c    | 63 +++++++++++++++++++++++++++++
 7 files changed, 135 insertions(+), 23 deletions(-)
 create mode 100644 newlib/libc/time/timegm.c

-- 
2.31.1

From b935001fcc817efe1187d993c076f65a7988e468 Mon Sep 17 00:00:00 2001
From: "R. Diez" <rdiezmail-newlib@yahoo.de>
Date: Mon, 3 May 2021 10:27:32 +0200
Subject: [PATCH 1/1] Refactor mktime and add the POSIX function timegm

Original author: Andrew Russell <ahrussell@google.com>
Signed-off-by: R. Diez <rdiezmail-newlib@yahoo.de>
---
 newlib/libc/include/time.h   |  3 ++
 newlib/libc/saber            |  1 +
 newlib/libc/time/Makefile.am |  2 +
 newlib/libc/time/Makefile.in |  9 +++++
 newlib/libc/time/local.h     |  2 +
 newlib/libc/time/mktime.c    | 78 +++++++++++++++++++++++++-----------
 newlib/libc/time/timegm.c    | 63 +++++++++++++++++++++++++++++
 7 files changed, 135 insertions(+), 23 deletions(-)
 create mode 100644 newlib/libc/time/timegm.c

diff --git a/newlib/libc/include/time.h b/newlib/libc/include/time.h
index ed6cc70fe..28aa978fc 100644
--- a/newlib/libc/include/time.h
+++ b/newlib/libc/include/time.h
@@ -56,6 +56,9 @@ struct tm
 clock_t	   clock (void);
 double	   difftime (time_t _time2, time_t _time1);
 time_t	   mktime (struct tm *_timeptr);
+#if __BSD_VISIBLE || __SVID_VISIBLE || __GNU_VISIBLE
+time_t    timegm (struct tm *_timeptr);
+#endif // __BSD_VISIBLE || __SVID_VISIBLE || __GNU_VISIBLE
 time_t	   time (time_t *_timer);
 #ifndef _REENT_ONLY
 char	  *asctime (const struct tm *_tblock);
diff --git a/newlib/libc/saber b/newlib/libc/saber
index 154eddf41..bdaef28fe 100644
--- a/newlib/libc/saber
+++ b/newlib/libc/saber
@@ -122,6 +122,7 @@ time/gmtime.c
 time/localtime.c
 time/mktime.c
 time/strftime.c
+time/timegm.c
 
 
 load stdio/fiprintf.c
diff --git a/newlib/libc/time/Makefile.am b/newlib/libc/time/Makefile.am
index be040baec..5c73c3a17 100644
--- a/newlib/libc/time/Makefile.am
+++ b/newlib/libc/time/Makefile.am
@@ -17,6 +17,7 @@ LIB_SOURCES = \
 	lcltime.c	\
 	lcltime_r.c	\
 	mktime.c	\
+	timegm.c	\
 	month_lengths.c \
 	strftime.c  	\
 	strptime.c	\
@@ -54,6 +55,7 @@ CHEWOUT_FILES = \
 	gmtime.def	\
 	lcltime.def	\
 	mktime.def	\
+	timegm.def	\
 	strftime.def	\
 	time.def	\
 	tzlock.def	\
diff --git a/newlib/libc/time/Makefile.in b/newlib/libc/time/Makefile.in
index ce6b6c183..b20ae09c4 100644
--- a/newlib/libc/time/Makefile.in
+++ b/newlib/libc/time/Makefile.in
@@ -80,6 +80,7 @@ am__objects_1 = lib_a-asctime.$(OBJEXT) lib_a-asctime_r.$(OBJEXT) \
 	lib_a-lcltime_r.$(OBJEXT) lib_a-mktime.$(OBJEXT) \
 	lib_a-month_lengths.$(OBJEXT) lib_a-strftime.$(OBJEXT) \
 	lib_a-strptime.$(OBJEXT) lib_a-time.$(OBJEXT) \
+	lib_a-timegm.$(OBJEXT) \
 	lib_a-tzcalc_limits.$(OBJEXT) lib_a-tzlock.$(OBJEXT) \
 	lib_a-tzset.$(OBJEXT) lib_a-tzset_r.$(OBJEXT) \
 	lib_a-tzvars.$(OBJEXT) lib_a-wcsftime.$(OBJEXT)
@@ -91,6 +92,7 @@ am__objects_2 = asctime.lo asctime_r.lo clock.lo ctime.lo ctime_r.lo \
 	difftime.lo gettzinfo.lo gmtime.lo gmtime_r.lo lcltime.lo \
 	lcltime_r.lo mktime.lo month_lengths.lo strftime.lo \
 	strptime.lo time.lo tzcalc_limits.lo tzlock.lo tzset.lo \
+	timegm.lo \
 	tzset_r.lo tzvars.lo wcsftime.lo
 @USE_LIBTOOL_TRUE@am_libtime_la_OBJECTS = $(am__objects_2)
 libtime_la_OBJECTS = $(am_libtime_la_OBJECTS)
@@ -283,6 +285,7 @@ LIB_SOURCES = \
 	strftime.c  	\
 	strptime.c	\
 	time.c		\
+	timegm.c	\
 	tzcalc_limits.c \
 	tzlock.c	\
 	tzset.c		\
@@ -464,6 +467,12 @@ lib_a-mktime.o: mktime.c
 lib_a-mktime.obj: mktime.c
 	$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) $(CPPFLAGS) $(lib_a_CFLAGS) $(CFLAGS) -c -o lib_a-mktime.obj `if test -f 'mktime.c'; then $(CYGPATH_W) 'mktime.c'; else $(CYGPATH_W) '$(srcdir)/mktime.c'; fi`
 
+lib_a-timegm.o: timegm.c
+	$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) $(CPPFLAGS) $(lib_a_CFLAGS) $(CFLAGS) -c -o lib_a-timegm.o `test -f 'timegm.c' || echo '$(srcdir)/'`timegm.c
+
+lib_a-timegm.obj: timegm.c
+	$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) $(CPPFLAGS) $(lib_a_CFLAGS) $(CFLAGS) -c -o lib_a-timegm.obj `if test -f 'timegm.c'; then $(CYGPATH_W) 'timegm.c'; else $(CYGPATH_W) '$(srcdir)/timegm.c'; fi`
+
 lib_a-month_lengths.o: month_lengths.c
 	$(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) $(CPPFLAGS) $(lib_a_CFLAGS) $(CFLAGS) -c -o lib_a-month_lengths.o `test -f 'month_lengths.c' || echo '$(srcdir)/'`month_lengths.c
 
diff --git a/newlib/libc/time/local.h b/newlib/libc/time/local.h
index bfe06e622..557187e0e 100644
--- a/newlib/libc/time/local.h
+++ b/newlib/libc/time/local.h
@@ -39,3 +39,5 @@ void _tzset_unlocked (void);
 void __tz_lock (void);
 void __tz_unlock (void);
 
+time_t __mktime_internal (struct tm *tim_p);
+void __set_tm_wday (long days, struct tm *tim_p);
diff --git a/newlib/libc/time/mktime.c b/newlib/libc/time/mktime.c
index 02032599a..c2717b08c 100644
--- a/newlib/libc/time/mktime.c
+++ b/newlib/libc/time/mktime.c
@@ -11,6 +11,8 @@
  * represented, returns the value (time_t) -1.
  *
  * Modifications:	Fixed tm_isdst usage - 27 August 2008 Craig Howland.
+ * 			Refactor code from mktime.c to share internal
+ * 			functions. - 17 July 2018 Andrew Russell.
  */
 
 /*
@@ -44,25 +46,36 @@ ANSI C requires <<mktime>>.
 
 #include <stdlib.h>
 #include <time.h>
+#include <stdint.h>
 #include "local.h"
 
 #define _SEC_IN_MINUTE 60L
 #define _SEC_IN_HOUR 3600L
 #define _SEC_IN_DAY 86400L
 
-static const int DAYS_IN_MONTH[12] =
+static const uint_least8_t DAYS_IN_MONTH[12] =
 {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
 
 #define _DAYS_IN_MONTH(x) ((x == 1) ? days_in_feb : DAYS_IN_MONTH[x])
 
-static const int _DAYS_BEFORE_MONTH[12] =
+static const uint_least16_t _DAYS_BEFORE_MONTH[12] =
 {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334};
 
-#define _ISLEAP(y) (((y) % 4) == 0 && (((y) % 100) != 0 || (((y)+1900) % 400) == 0))
-#define _DAYS_IN_YEAR(year) (_ISLEAP(year) ? 366 : 365)
+/* returns either 0 or 1 */
+static int
+__is_leap_year (int year)
+{
+  return (year % 4) == 0 && ((year % 100) != 0 || (((year / 100) & 3) == (-(YEAR_BASE / 100)  & 3)));
+}
+
+static int
+__days_in_year (int year)
+{
+  return __is_leap_year(year) ? 366 : 365;
+}
 
-static void 
-validate_structure (struct tm *tim_p)
+static void
+__validate_tm_structure (struct tm *tim_p)
 {
   div_t res;
   int days_in_feb = 28;
@@ -112,7 +125,7 @@ validate_structure (struct tm *tim_p)
         }
     }
 
-  if (_DAYS_IN_YEAR (tim_p->tm_year) == 366)
+  if (__days_in_year(tim_p->tm_year) == 366)
     days_in_feb = 29;
 
   if (tim_p->tm_mday <= 0)
@@ -124,7 +137,7 @@ validate_structure (struct tm *tim_p)
 	      tim_p->tm_year--;
 	      tim_p->tm_mon = 11;
 	      days_in_feb =
-		((_DAYS_IN_YEAR (tim_p->tm_year) == 366) ?
+	        ((__days_in_year(tim_p->tm_year) == 366) ?
 		 29 : 28);
 	    }
 	  tim_p->tm_mday += _DAYS_IN_MONTH (tim_p->tm_mon);
@@ -140,15 +153,23 @@ validate_structure (struct tm *tim_p)
 	      tim_p->tm_year++;
 	      tim_p->tm_mon = 0;
 	      days_in_feb =
-		((_DAYS_IN_YEAR (tim_p->tm_year) == 366) ?
+	        ((__days_in_year(tim_p->tm_year) == 366) ?
 		 29 : 28);
 	    }
 	}
     }
 }
 
-time_t 
-mktime (struct tm *tim_p)
+void
+__set_tm_wday (long days, struct tm *tim_p)
+{
+  if ((tim_p->tm_wday = (days + 4) % 7) < 0)
+    tim_p->tm_wday += 7;
+}
+
+/* Assumes the time at tim_p is a UTC time and returns its arithmetic representation */
+time_t
+__mktime_internal (struct tm *tim_p)
 {
   time_t tim = 0;
   long days = 0;
@@ -156,7 +177,7 @@ mktime (struct tm *tim_p)
   __tzinfo_type *tz = __gettzinfo ();
 
   /* validate structure */
-  validate_structure (tim_p);
+  __validate_tm_structure (tim_p);
 
   /* compute hours, minutes, seconds */
   tim += tim_p->tm_sec + (tim_p->tm_min * _SEC_IN_MINUTE) +
@@ -165,7 +186,7 @@ mktime (struct tm *tim_p)
   /* compute days in year */
   days += tim_p->tm_mday - 1;
   days += _DAYS_BEFORE_MONTH[tim_p->tm_mon];
-  if (tim_p->tm_mon > 1 && _DAYS_IN_YEAR (tim_p->tm_year) == 366)
+  if (tim_p->tm_mon > 1 && __days_in_year(tim_p->tm_year) == 366)
     days++;
 
   /* compute day of the year */
@@ -178,17 +199,29 @@ mktime (struct tm *tim_p)
   if ((year = tim_p->tm_year) > 70)
     {
       for (year = 70; year < tim_p->tm_year; year++)
-	days += _DAYS_IN_YEAR (year);
+	days += __days_in_year(year);
     }
   else if (year < 70)
     {
       for (year = 69; year > tim_p->tm_year; year--)
-	days -= _DAYS_IN_YEAR (year);
-      days -= _DAYS_IN_YEAR (year);
+	days -= __days_in_year(year);
+      days -= __days_in_year(year);
     }
 
   /* compute total seconds */
-  tim += (time_t)days * _SEC_IN_DAY;
+  tim += (days * _SEC_IN_DAY);
+
+  return tim;
+}
+
+time_t
+mktime (struct tm *tim_p)
+{
+  time_t tim = __mktime_internal(tim_p);
+  long days = tim / SECSPERDAY;
+  int year = tim_p->tm_year;
+  int isdst=0;
+  __tzinfo_type *tz = __gettzinfo ();
 
   TZ_LOCK;
 
@@ -237,7 +270,7 @@ mktime (struct tm *tim_p)
 		  tim_p->tm_sec += diff;
 		  tim += diff;  /* we also need to correct our current time calculation */
 		  int mday = tim_p->tm_mday;
-		  validate_structure (tim_p);
+		  __validate_tm_structure(tim_p);
 		  mday = tim_p->tm_mday - mday;
 		  /* roll over occurred */
 		  if (mday) {
@@ -251,9 +284,9 @@ mktime (struct tm *tim_p)
 		    /* handle yday */
 		    if ((tim_p->tm_yday += mday) < 0) {
 			  --year;
-			  tim_p->tm_yday = _DAYS_IN_YEAR(year) - 1;
+			  tim_p->tm_yday = __days_in_year(year) - 1;
 		    } else {
-			  mday = _DAYS_IN_YEAR(year);
+			  mday = __days_in_year(year);
 			  if (tim_p->tm_yday > (mday - 1))
 				tim_p->tm_yday -= mday;
 		    }
@@ -275,8 +308,7 @@ mktime (struct tm *tim_p)
   tim_p->tm_isdst = isdst;
 
   /* compute day of the week */
-  if ((tim_p->tm_wday = (days + 4) % 7) < 0)
-    tim_p->tm_wday += 7;
-	
+  __set_tm_wday(days, tim_p);
+
   return tim;
 }
diff --git a/newlib/libc/time/timegm.c b/newlib/libc/time/timegm.c
new file mode 100644
index 000000000..ab50de7e1
--- /dev/null
+++ b/newlib/libc/time/timegm.c
@@ -0,0 +1,63 @@
+/*
+ * timegm.c
+ * Original Author: A. Russell
+ *
+ * Converts the broken-down time, expressed as UTC time, in the structure
+ * pointed to by tim_p into a calendar time value. The original values of the
+ * tm_wday and tm_yday fields of the structure are ignored, and the original
+ * values of the other fields have no restrictions. On successful completion
+ * the fields of the structure are set to represent the specified calendar
+ * time. Returns the specified calendar time. If the calendar time can not be
+ * represented, returns the value (time_t) -1.  These functions are nonstandard
+ * GNU extensions that are also present on the BSDs.  Avoid their use.
+ * Modifications: Refactored mktime.c to support both mktime and timegm
+                         - 23 July 2018 Andrew Russell.
+ */
+
+/*
+FUNCTION
+<<timegm>>---convert time to arithmetic representation
+
+INDEX
+ timegm
+
+SYNOPSIS
+ #include <time.h>
+ time_t timegm(struct tm *<[timp]>);
+
+DESCRIPTION
+<<timegm>> assumes the time at <[timp]> is a UTC time, and converts
+its representation from the traditional representation defined by
+<<struct tm>> into a representation suitable for arithmetic.
+
+<<timegm>> is the inverse of <<gmtime>>.
+
+RETURNS
+If the contents of the structure at <[timp]> do not form a valid
+calendar time representation, the result is <<-1>>.  Otherwise, the
+result is the time, converted to a <<time_t>> value.
+
+PORTABILITY
+<<timegm>> is a nonstandard GNU extension to POSIX also present on BSD.
+
+<<timegm>> requires no supporting OS subroutines.
+*/
+
+#include <stdlib.h>
+#include <time.h>
+#include "local.h"
+
+time_t
+timegm (struct tm *tim_p)
+{
+  time_t tim = __mktime_internal(tim_p);
+  long days = tim / SECSPERDAY;
+
+  /* set isdst flag to 0 since we are in UTC */
+  tim_p->tm_isdst = 0;
+
+  /* compute day of the week */
+  __set_tm_wday(days, tim_p);
+
+  return tim;
+}
-- 
2.31.1