Add routines to convert time_t to/from fixed-bit fields. These routines

serve two purposes: (1) so we can maintain backwards compatibility with
protocols (rwhod, dump, etc...) that either assume time_t is 32 bits or
assume sizeof(time_t) == sizeof(int), or make other similar assumptions.
(2) To tag such routines (by the presence of these calls) for future
cleanup/extension work.

The 32->64 routine, time32_to_time() (when time_t is 64 bits, that is),
is defined specifically to implement temporal locality to properly set the
msb bits of a 64 bit time_t quantity, using the 50 year rule.  The locality
code has not been implemented yet (and doesn't need to be for a while),
but that is the intent.   This will allow us to maintain backwards protocol
compatibility past 2038.

These routines are intended to be platform and time_t agnostic.

MFC after:	1 week

include/time.h

@@ -135,6 +135,13 @@ time_t mktime __P((struct tm *));
 size_t strftime __P((char *, size_t, const char *, const struct tm *));
 time_t time __P((time_t *));
 
+#ifndef _ANSI_SOURCE
+time_t time32_to_time __P((__int32_t t32));
+__int32_t time_to_time32 __P((time_t t));
+time_t time64_to_time __P((__int64_t t64));
+__int64_t time_to_time64 __P((time_t t));
+#endif /* not ANSI */
+
 #ifndef _ANSI_SOURCE
 void tzset __P((void));
 #endif /* not ANSI */

lib/libc/stdtime/Makefile.inc

@@ -3,7 +3,8 @@
 
 .PATH:	${.CURDIR}/../libc/stdtime ${.CURDIR}/../locale
 
-SRCS+=	asctime.c difftime.c localtime.c strftime.c strptime.c timelocal.c
+SRCS+=	asctime.c difftime.c localtime.c strftime.c strptime.c timelocal.c \
+	time32.c
 
 .if ${LIB} == "c"
 MAN+=	ctime.3 strftime.3 strptime.3 time2posix.3

lib/libc/stdtime/time32.c

@@ -0,0 +1,60 @@
+/*-
+ * Copyright (c) 2001 FreeBSD Inc.
+ * All rights reserved.
+ *
+ * These routines are for converting time_t to fixed-bit representations
+ * for use in protocols or storage.  When converting time to a larger
+ * representation of time_t these routines are expected to assume temporal
+ * locality and use the 50-year rule to properly set the msb bits.  XXX
+ *
+ * Redistribution and use under the terms of the COPYRIGHT file at the
+ * base of the source tree.
+ *
+ * $FreeBSD$
+ */
+
+#include <sys/types.h>
+#include <sys/time.h>
+
+/*
+ * Convert a 32 bit representation of time_t into time_t.  XXX needs to
+ * implement the 50-year rule to handle post-2038 conversions.
+ */
+time_t
+time32_to_time(__int32_t t32)
+{
+    return((time_t)t32);
+}
+
+/*
+ * Convert time_t to a 32 bit representation.  If time_t is 64 bits we can
+ * simply chop it down.   The resulting 32 bit representation can be 
+ * converted back to a temporally local 64 bit time_t using time32_to_time.
+ */
+__int32_t
+time_to_time32(time_t t)
+{
+    return((__int32_t)t);
+}
+
+/*
+ * Convert a 64 bit representation of time_t into time_t.  If time_t is
+ * represented as 32 bits we can simply chop it and not support times
+ * past 2038.
+ */
+time_t
+time64_to_time(__int64_t t64)
+{
+    return((time_t)t64);
+}
+
+/*
+ * Convert time_t to a 64 bit representation.  If time_t is represented
+ * as 32 bits we simply sign-extend and do not support times past 2038.
+ */
+__int64_t
+time_to_time64(time_t t)
+{
+    return((__int64_t)t);
+}
+