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Here's an example I cooked up a few years ago that accomplishes
exactly this. Works on FreeBSD. ("make tryit")
John
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# This is a shell archive. Save it in a file, remove anything before
# this line, and then unpack it by entering "sh file". Note, it may
# create directories; files and directories will be owned by you and
# have default permissions.
#
# This archive contains:
#
# Makefile
# timeskew.c
#
echo x - Makefile
sed 's/^X//' >Makefile << 'END-of-Makefile'
XNOPROFILE=1
XINTERNALLIB=1
XSHLIB_MAJOR=1
XSHLIB_MINOR=0
X
XLIB= timeskew
XSRCS= timeskew.c
X
Xtryit: lib$(LIB).so.1.0
X @echo 'puts [clock format [clock seconds]]' | tclsh
X @echo 'puts [clock format [clock seconds]]' | \
X env LD_PRELOAD=./libtimeskew.so.1.0 tclsh
X
X.include <bsd.lib.mk>
END-of-Makefile
echo x - timeskew.c
sed 's/^X//' >timeskew.c << 'END-of-timeskew.c'
X/*
X * Coerces the return value from gettimeofday() to always fall within
X * the time range starting at BASEDATE and ending at BASEDATE+TIMESPAN
X *
X * Todo: pick up BASEDATE and TIMESPAN from env variables
X */
X
X#include <sys/time.h>
X#include <sys/syscall.h>
X
X#ifndef BASEDATE
X#define BASEDATE 820472400 /* 1 Jan 1996 00:00:00 */
X
X#define TIMESPAN ONELEAPYEAR
X/* really only want until 29 Dec 1996 (851835600), but this will do */
X#endif
X
X#define ONEDAY (24*60*60)
X#define ONEMONTH (ONEDAY*31)
X#define ONEYEAR (ONEDAY*365)
X#define ONELEAPYEAR (ONEDAY*366)
X
X#ifndef TIMESPAN
X#define TIMESPAN ONEMONTH
X#endif
X
Xint
Xgettimeofday(struct timeval *tp, struct timezone *tzp) {
X int ret;
X
X ret = __syscall(SYS_gettimeofday, 2, tp, tzp);
X if (ret == 0 && tp != NULL) {
X tp->tv_sec = ((tp->tv_sec - BASEDATE) % TIMESPAN) + BASEDATE;
X }
X return ret;
X}
X
END-of-timeskew.c
exit
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This archive was generated by hypermail 2b30 : Fri Apr 13 2001 - 14:45:57 PDT