make [clock format] go faster

1 files changed, 1211 insertions, 191 deletions

diff --git a/generic/tclClock.c b/generic/tclClock.c
index 71dec02..3dc93fa 100644
--- a/generic/tclClock.c
+++ b/generic/tclClock.c
@@ -12,7 +12,7 @@
  * See the file "license.terms" for information on usage and redistribution of
  * this file, and for a DISCLAIMER OF ALL WARRANTIES.
  *
- * RCS: @(#) $Id: tclClock.c,v 1.42 2005/11/01 15:30:52 dkf Exp $
+ * RCS: @(#) $Id: tclClock.c,v 1.43 2005/11/29 22:50:58 kennykb Exp $
  */
 
 #include "tclInt.h"
@@ -26,6 +26,92 @@
 #endif
 
 /*
+ * Constants
+ */
+
+#define JULIAN_SEC_POSIX_EPOCH		((Tcl_WideInt) 210866803200)
+#define SECONDS_PER_DAY			86400
+#define FOUR_CENTURIES			146097 /* days */
+#define JDAY_1_JAN_1_CE_JULIAN		1721424
+#define JDAY_1_JAN_1_CE_GREGORIAN	1721426
+#define ONE_CENTURY_GREGORIAN		36524  /* days */
+#define FOUR_YEARS			1461   /* days */
+#define ONE_YEAR			365    /* days */
+
+/*
+ * Table of the days in each month, leap and common years
+ */
+
+static const int hath[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}
+};
+static const int daysInPriorMonths[2][13] = {
+    {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365},
+    {0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366}
+};
+
+/*
+ * Enumeration of the string literals used in [clock]
+ */
+
+typedef enum ClockLiteral {
+    LIT_BCE,		LIT_CE,		    
+    LIT_DAYOFMONTH,	LIT_DAYOFWEEK,	    LIT_DAYOFYEAR,
+    LIT_ERA,            LIT_GREGORIAN,	
+    LIT_ISO8601WEEK,	LIT_ISO8601YEAR,
+    LIT_JULIANDAY,	LIT_LOCALSECONDS,
+    LIT_MONTH,
+    LIT_SECONDS,	LIT_TZNAME,	    LIT_TZOFFSET,
+    LIT_YEAR,
+    LIT__END
+} ClockLiteral;
+static const char *const literals[] = {
+    "BCE",		"CE",		    
+    "dayOfMonth",	"dayOfWeek",	    "dayOfYear",
+    "era",	        "gregorian",	
+    "iso8601Week",	"iso8601Year",
+    "julianDay",	"localSeconds",
+    "month",
+    "seconds",		"tzName",      	    "tzOffset",
+    "year"
+};
+
+/*
+ * Structure containing the client data for [clock]
+ */
+
+typedef struct ClockClientData {
+    int refCount;		/* Number of live references */
+    Tcl_Obj** literals;		/* Pool of object literals */
+} ClockClientData;
+
+/*
+ * Structure containing the fields used in [clock format] and [clock scan]
+ */
+
+typedef struct TclDateFields {
+    Tcl_WideInt seconds;	/* Time expressed in seconds from the
+				 * Posix epoch */
+    Tcl_WideInt localSeconds;	/* Local time expressed in nominal seconds
+				 * from the Posix epoch */
+    int tzOffset;		/* Time zone offset in seconds east of
+				 * Greenwich */
+    Tcl_Obj* tzName;		/* Time zone name */
+    int julianDay;		/* Julian Day Number in local time zone */
+    enum {BCE=1, CE=0} era;	/* Era */
+    int gregorian;		/* Flag == 1 if the date is Gregorian */
+    int year;			/* Year of the era */
+    int dayOfYear;		/* Day of the year (1 January == 1) */
+    int month;			/* Month number */
+    int dayOfMonth;		/* Day of the month */
+    int iso8601Year;		/* ISO8601 week-based year */
+    int iso8601Week;		/* ISO8601 week number */
+    int dayOfWeek;		/* Day of the week */
+    
+} TclDateFields;
+
+/*
  * Thread specific data block holding a 'struct tm' for the 'gmtime' and
  * 'localtime' library calls.
  */
@@ -43,312 +129,1216 @@ TCL_DECLARE_MUTEX(clockMutex)
  * Function prototypes for local procedures in this file:
  */
 
+static int		ConvertUTCToLocal(Tcl_Interp*, 
+			    TclDateFields*, Tcl_Obj*, int);
+static int		ConvertUTCToLocalUsingTable(Tcl_Interp*, 
+			    TclDateFields*, int, Tcl_Obj *CONST[]);
+static int		ConvertUTCToLocalUsingC(Tcl_Interp*, 
+			    TclDateFields*, int);
+static int		ConvertLocalToUTC(Tcl_Interp*, 
+			    TclDateFields*, Tcl_Obj*, int);
+static int		ConvertLocalToUTCUsingTable(Tcl_Interp*, 
+			    TclDateFields*, int, Tcl_Obj *CONST[]);
+static int		ConvertLocalToUTCUsingC(Tcl_Interp*, 
+			    TclDateFields*, int);
+static Tcl_Obj*		LookupLastTransition(Tcl_Interp*, Tcl_WideInt,
+			    int, Tcl_Obj *CONST *);
+static void		GetYearWeekDay(TclDateFields*, int);
+static void		GetGregorianEraYearDay(TclDateFields*, int);
+static void		GetMonthDay(TclDateFields*);
+static void		GetJulianDayFromEraYearWeekDay(TclDateFields*, int);
+static void		GetJulianDayFromEraYearMonthDay(TclDateFields*, int);
+static int		IsGregorianLeapYear(TclDateFields*);
+static int		WeekdayOnOrBefore(int, int);
+static int		ClockClicksObjCmd(
+			    ClientData clientData, Tcl_Interp *interp,
+			    int objc, Tcl_Obj *CONST objv[]);
+static int		ClockConvertlocaltoutcObjCmd(
+			    ClientData clientData, Tcl_Interp *interp,
+			    int objc, Tcl_Obj *CONST objv[]);
+static int		ClockGetdatefieldsObjCmd(
+			    ClientData clientData, Tcl_Interp *interp,
+			    int objc, Tcl_Obj *CONST objv[]);
+static int		ClockGetenvObjCmd(
+			    ClientData clientData, Tcl_Interp *interp,
+			    int objc, Tcl_Obj *CONST objv[]);
+static int		ClockMicrosecondsObjCmd(
+			    ClientData clientData, Tcl_Interp *interp,
+			    int objc, Tcl_Obj *CONST objv[]);
+static int		ClockMillisecondsObjCmd(
+			    ClientData clientData, Tcl_Interp *interp,
+			    int objc, Tcl_Obj *CONST objv[]);
+static int		ClockSecondsObjCmd(
+			    ClientData clientData, Tcl_Interp *interp,
+			    int objc, Tcl_Obj *CONST objv[]);
 static struct tm *	ThreadSafeLocalTime(CONST time_t *);
 static void		TzsetIfNecessary(void);
+static void		ClockDeleteCmdProc(ClientData);
+
 
 /*
  *----------------------------------------------------------------------
  *
- * TclClockGetenvObjCmd --
+ * TclClockInit --
  *
- *	Tcl command that reads an environment variable from the system
+ *	Registers the 'clock' subcommands with the Tcl interpreter
+ *	and initializes its client data (which consists mostly of
+ *	constant Tcl_Obj's that it is too much trouble to keep
+ *	recreating).
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	Installs the commands and creates the client data
+ *
+ *----------------------------------------------------------------------
+ */
+
+void
+TclClockInit(
+    Tcl_Interp* interp		/* Tcl interpreter */
+) {
+    int i;
+
+    /* Create the client data */
+
+    ClockClientData *data =
+	(ClockClientData*) ckalloc(sizeof(ClockClientData));
+    data->refCount = 0;
+    
+    /*
+     * Create the literal pool
+     */
+    data->literals = (Tcl_Obj**) ckalloc(LIT__END * sizeof(Tcl_Obj*));
+    for (i = 0; i < LIT__END; ++i) {
+	data->literals[i] = Tcl_NewStringObj(literals[i], -1);
+	Tcl_IncrRefCount(data->literals[i]);
+    }
+
+    /* Install the commands */
+
+    Tcl_CreateObjCommand(interp,	"::tcl::clock::clicks",
+	    ClockClicksObjCmd,	(ClientData) NULL, NULL);
+    Tcl_CreateObjCommand(interp,	"::tcl::clock::getenv",
+	    ClockGetenvObjCmd,	(ClientData) NULL, NULL);
+    Tcl_CreateObjCommand(interp,	"::tcl::clock::microseconds",
+	    ClockMicrosecondsObjCmd,	(ClientData) NULL, NULL);
+    Tcl_CreateObjCommand(interp,	"::tcl::clock::milliseconds",
+	    ClockMillisecondsObjCmd,	(ClientData) NULL, NULL);
+    Tcl_CreateObjCommand(interp,	"::tcl::clock::seconds",
+	    ClockSecondsObjCmd,	(ClientData) NULL, NULL);
+    Tcl_CreateObjCommand(interp,	"::tcl::clock::Oldscan",
+	    TclClockOldscanObjCmd,	(ClientData) NULL, NULL);
+    Tcl_CreateObjCommand(interp,	"::tcl::clock::ConvertLocalToUTC",
+	    ClockConvertlocaltoutcObjCmd, (ClientData) data,
+	    ClockDeleteCmdProc);
+    Tcl_CreateObjCommand(interp,	"::tcl::clock::GetDateFields",
+	    ClockGetdatefieldsObjCmd,(ClientData) data,
+	    ClockDeleteCmdProc);
+    ++data->refCount;
+
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * ClockConvertlocaltoutcObjCmd --
+ *
+ *	Tcl command that converts a UTC time to a local time by
+ *	whatever means is available.
  *
  * Usage:
- *	::tcl::clock::getEnv NAME
+ *	::tcl::clock::ConvertUTCToLocal dictionary tzdata changeover
  *
  * Parameters:
- *	NAME - Name of the environment variable desired
+ *	dict - Dictionary containing a 'localSeconds' entry.
+ *	tzdata - Time zone data
+ *	changeover - Julian Day of the adoption of the Gregorian calendar.
  *
  * Results:
- *	Returns a standard Tcl result.  Returns an error if the
- *	variable does not exist, with a message left in the interpreter.
- *	Returns TCL_OK and the value of the variable if the variable
- *	does exist,
+ *	Returns a standard Tcl result.
+ *
+ * Side effects:
+ *	On success, sets the interpreter result to the given dictionary
+ *	augmented with a 'seconds' field giving the UTC time.  On failure,
+ *	leaves an error message in the interpreter result.
  *
  *----------------------------------------------------------------------
  */
 
-int
-TclClockGetenvObjCmd(
-    ClientData clientData,
-    Tcl_Interp* interp,
-    int objc,
-    Tcl_Obj *CONST objv[])
-{
+static int
+ClockConvertlocaltoutcObjCmd(
+    ClientData clientData,	/* Client data  */
+    Tcl_Interp* interp,		/* Tcl interpreter */
+    int objc,			/* Parameter count */
+    Tcl_Obj *CONST * objv	/* Parameter vector */
+) {
+    ClockClientData* data = (ClockClientData*) clientData;
+    Tcl_Obj* CONST * literals = data->literals;
+    Tcl_Obj* secondsObj;
+    Tcl_Obj* dict;
+    int changeover;
+    TclDateFields fields;
+    int created = 0;
+    int status;
 
-    CONST char* varName;
-    CONST char* varValue;
+    /* Check params and convert time */
 
-    if (objc != 2) {
-	Tcl_WrongNumArgs(interp, 1, objv, "name");
+    if (objc != 4) {
+	Tcl_WrongNumArgs(interp, 1, objv, "dict tzdata changeover");
 	return TCL_ERROR;
     }
-    varName = Tcl_GetStringFromObj(objv[1], NULL);
-    varValue = getenv(varName);
-    if (varValue == NULL) {
-	Tcl_SetObjResult(interp,
-		Tcl_NewStringObj("variable not found", -1));
+    dict = objv[1];
+    if ((Tcl_DictObjGet(interp, dict, literals[LIT_LOCALSECONDS], &secondsObj)
+	 != TCL_OK)
+	|| (Tcl_GetWideIntFromObj(interp, secondsObj, &(fields.localSeconds))
+	    != TCL_OK)
+	|| (Tcl_GetIntFromObj(interp, objv[3], &changeover) != TCL_OK)
+	|| ConvertLocalToUTC(interp, &fields, objv[2], changeover)) {
 	return TCL_ERROR;
-    } else {
-	Tcl_SetObjResult(interp, Tcl_NewStringObj(varValue, -1));
-	return TCL_OK;
     }
+
+    /* 
+     * Copy-on-write; set the 'seconds' field in the dictionary and
+     * place the modified dictionary in the interpreter result.
+     */
+
+    if (Tcl_IsShared(dict)) {
+	dict = Tcl_DuplicateObj(dict);
+	created = 1;
+	Tcl_IncrRefCount(dict);
+    }
+    status = Tcl_DictObjPut(interp, dict, literals[LIT_SECONDS],
+			    Tcl_NewWideIntObj(fields.seconds));
+    if (status == TCL_OK) {
+	Tcl_SetObjResult(interp, dict);
+    }
+    if (created) {
+	Tcl_DecrRefCount(dict);
+    }
+    return status;
 }
 
 /*
- *-------------------------------------------------------------------------
+ *----------------------------------------------------------------------
  *
- * TclClockLocaltimeObjCmd --
+ * ClockGetdatefieldsObjCmd --
  *
- *	Tcl command that extracts local time using the C library to do
- *	it.
+ *	Tcl command that determines the values that [clock format] will
+ *	use in formatting a date, and populates a dictionary with them.
  *
  * Usage:
- *	::tcl::clock::Localtime <tick>
+ *	::tcl::clock::GetDateFields seconds tzdata changeover
  *
  * Parameters:
- *	<tick> -- A count of seconds from the Posix epoch.
+ *	seconds - Time expressed in seconds from the Posix epoch.
+ *	tzdata - Time zone data of the time zone in which time is to 
+ *                 be expressed.
+ *	changeover - Julian Day Number at which the current locale adopted
+ *		     the Gregorian calendar
  *
  * Results:
+ *	Returns a dictonary populated with the fields:
+ *		seconds - Seconds from the Posix epoch
+ *		localSeconds - Nominal seconds from the Posix epoch in
+ *			       the local time zone.
+ *		tzOffset - Time zone offset in seconds east of Greenwich
+ *		tzName - Time zone name
+ *		julianDay - Julian Day Number in the local time zone
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+ClockGetdatefieldsObjCmd(
+    ClientData clientData,	/* Opaque pointer to literal pool, etc. */
+    Tcl_Interp* interp,		/* Tcl interpreter */
+    int objc,			/* Parameter count */
+    Tcl_Obj *CONST *objv	/* Parameter vector */
+) {
+    TclDateFields fields;
+    Tcl_Obj* dict;
+    ClockClientData* data = (ClockClientData*) clientData;
+    Tcl_Obj* CONST * literals = data->literals;
+    int changeover;
 
- *	Returns a standard Tcl result.  The object result is a Tcl
- *	list containing the year, month, day, hour, minute, and second
- *	fields of the local time.  It may return an error if the
- *	argument exceeds the arithmetic range representable by
- *	'time_t'.
+    /* Check params */
+
+    if (objc != 4) {
+	Tcl_WrongNumArgs(interp, 1, objv, "seconds tzdata changeover");
+	return TCL_ERROR;
+    }
+    if (Tcl_GetWideIntFromObj(interp, objv[1], &(fields.seconds)) != TCL_OK
+	|| Tcl_GetIntFromObj(interp, objv[3], &changeover) != TCL_OK) {
+	return TCL_ERROR;
+    }
+
+    /* Convert UTC time to local */
+
+    if (ConvertUTCToLocal(interp, &fields, objv[2], changeover) != TCL_OK) {
+	return TCL_ERROR;
+    }
+
+    /* Extract Julian day */
+
+    fields.julianDay = (int) ((fields.localSeconds + JULIAN_SEC_POSIX_EPOCH)
+			      / SECONDS_PER_DAY);
+
+    /* Convert to Julian or Gregorian calendar */
+
+    GetGregorianEraYearDay(&fields, changeover);
+    GetMonthDay(&fields);
+    GetYearWeekDay(&fields, changeover);
+
+    dict = Tcl_NewDictObj();
+    Tcl_DictObjPut((Tcl_Interp*) NULL, dict, literals[LIT_LOCALSECONDS],
+		   Tcl_NewWideIntObj(fields.localSeconds));
+    Tcl_DictObjPut((Tcl_Interp*) NULL, dict, literals[LIT_SECONDS],
+		   Tcl_NewWideIntObj(fields.seconds));
+    Tcl_DictObjPut((Tcl_Interp*) NULL, dict, literals[LIT_TZNAME],
+		   fields.tzName);
+    Tcl_DecrRefCount(fields.tzName);
+    Tcl_DictObjPut((Tcl_Interp*) NULL, dict, literals[LIT_TZOFFSET],
+		   Tcl_NewIntObj(fields.tzOffset));
+    Tcl_DictObjPut((Tcl_Interp*) NULL, dict, literals[LIT_JULIANDAY],
+		   Tcl_NewWideIntObj(fields.julianDay));
+    Tcl_DictObjPut((Tcl_Interp*) NULL, dict, literals[LIT_GREGORIAN],
+		   Tcl_NewIntObj(fields.gregorian));
+    Tcl_DictObjPut((Tcl_Interp*) NULL, dict, literals[LIT_ERA],
+		   literals[fields.era ? LIT_BCE : LIT_CE]);
+    Tcl_DictObjPut((Tcl_Interp*) NULL, dict, literals[LIT_YEAR],
+		   Tcl_NewIntObj(fields.year));
+    Tcl_DictObjPut((Tcl_Interp*) NULL, dict, literals[LIT_DAYOFYEAR],
+		   Tcl_NewIntObj(fields.dayOfYear));
+    Tcl_DictObjPut((Tcl_Interp*) NULL, dict, literals[LIT_MONTH],
+		   Tcl_NewIntObj(fields.month));
+    Tcl_DictObjPut((Tcl_Interp*) NULL, dict, literals[LIT_DAYOFMONTH],
+		   Tcl_NewIntObj(fields.dayOfMonth));
+    Tcl_DictObjPut((Tcl_Interp*) NULL, dict, literals[LIT_ISO8601YEAR],
+		   Tcl_NewIntObj(fields.iso8601Year));
+    Tcl_DictObjPut((Tcl_Interp*) NULL, dict, literals[LIT_ISO8601WEEK],
+		   Tcl_NewIntObj(fields.iso8601Week));
+    Tcl_DictObjPut((Tcl_Interp*) NULL, dict, literals[LIT_DAYOFWEEK],
+		   Tcl_NewIntObj(fields.dayOfWeek));
+    Tcl_SetObjResult(interp, dict);
+
+    return TCL_OK;
+}
+
+/*
+ *----------------------------------------------------------------------
  *
- * Side effects:
- *	None.
+ * ConvertLocalToUTC --
+ *
+ *	Converts a time (in a TclDateFields structure) from the
+ *	local wall clock to UTC.
+ *
+ * Results:
+ *	Returns a standard Tcl result.
  *
- * This function is used as a call of last resort if the current time
- * zone cannot be determined from environment variables TZ or TCL_TZ.
- * It attempts to use the 'localtime' library function to extract the
- * time and return it that way.  This method suffers from Y2038 problems
- * on most platforms.  It also provides no portable way to get the
- * name of the time zone.
+ * Side effects:
+ *	Populates the 'seconds' field if successful; stores an error
+ *	message in the interpreter result on failure.
  *
- *-------------------------------------------------------------------------
+ *----------------------------------------------------------------------
  */
 
-int
-TclClockLocaltimeObjCmd(
-    ClientData clientData,	/* Unused */
+static int
+ConvertLocalToUTC(
     Tcl_Interp* interp,		/* Tcl interpreter */
-    int objc,			/* Parameter count */
-    Tcl_Obj* CONST* objv)	/* Parameter vector */
-{
-    Tcl_WideInt tick;		/* Time to convert */
-    time_t tock;
-    struct tm* timeVal;		/* Time after conversion */
+    TclDateFields* fields,	/* Fields of the time */
+    Tcl_Obj* tzdata,		/* Time zone data */
+    int changeover		/* Julian Day of the Gregorian transition */
+) {
+    int rowc;			/* Number of rows in tzdata */
+    Tcl_Obj** rowv;		/* Pointers to the rows */
 
-    Tcl_Obj* returnVec[ 6 ];
+    /* unpack the tz data */
+
+    if (Tcl_ListObjGetElements(interp, tzdata, &rowc, &rowv) != TCL_OK) {
+	return TCL_ERROR;
+    }
+
+    /* 
+     * Special case: If the time zone is :localtime, the tzdata will be empty.
+     * Use 'mktime' to convert the time to local
+     */
+
+    if (rowc == 0) {
+	return ConvertLocalToUTCUsingC(interp, fields, changeover);
+    } else {
+	return ConvertLocalToUTCUsingTable(interp, fields, rowc, rowv);
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * ConvertLocalToUTCUsingTable --
+ *
+ *	Converts a time (in a TclDateFields structure) from local time
+ *	in a given time zone to UTC.
+ *
+ * Results:
+ *	Returns a standard Tcl result.
+ *
+ * Side effects:
+ *	Stores an error message in the interpreter if an error occurs;
+ *	if successful, stores the 'seconds' field in 'fields.
+ *
+ *----------------------------------------------------------------------
+ */
+static int
+ConvertLocalToUTCUsingTable(
+    Tcl_Interp* interp,		/* Tcl interpreter */
+    TclDateFields* fields,	/* Time to convert, with 'seconds' filled in */
+    int rowc,			/* Number of points at which time changes */
+    Tcl_Obj *CONST rowv[]	/* Points at which time changes */
+) {
+    Tcl_Obj* row;
+    int cellc;
+    Tcl_Obj** cellv;
+    int have[8];
+    int nHave = 0;
+    int i;
+    int found;
 
     /*
-     * Check args
+     * Perform an initial lookup assuming that local == UTC, and locate
+     * the last time conversion prior to that time.  Get the offset from
+     * that row, and look up again.  Continue until we find an offset
+     * that we found before. This definition, rather than "the same offset"
+     * ensures that we don't enter an endless loop, as would otherwise happen
+     * when trying to convert a non-existent time such as 02:30 during
+     * the US Spring Daylight Saving Time transition.
      */
 
-    if (objc != 2) {
-	Tcl_WrongNumArgs(interp, 1, objv, "seconds");
+    found = 0;
+    fields->tzOffset = 0;
+    fields->seconds = fields->localSeconds;
+    while (!found) {
+	row = LookupLastTransition(interp, fields->seconds, rowc, rowv);
+	if ((row == NULL)
+	    || (Tcl_ListObjGetElements(interp, row, &cellc, &cellv) != TCL_OK) 
+	    || (Tcl_GetIntFromObj(interp, cellv[1], &(fields->tzOffset))
+		!= TCL_OK)) {
+	    return TCL_ERROR;
+	}
+	found = 0;
+	for (i = 0; !found && i < nHave; ++i) {
+	    if (have[i] == fields->tzOffset) {
+		found = 1;
+		break;
+	    } 
+	}
+	if (!found) {
+	    if (nHave == 8) {
+		Tcl_Panic("loop in ConvertLocalToUTCUsingTable");
+	    }
+	    have[nHave] = fields->tzOffset;
+	    ++nHave;
+	}
+	fields->seconds = fields->localSeconds - fields->tzOffset;
+    }
+    fields->tzOffset = have[i];
+    fields->seconds = fields->localSeconds - fields->tzOffset;
+    return TCL_OK;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * ConvertLocalToUTCUsingC --
+ *
+ *	Converts a time from local wall clock to UTC when the local
+ *	time zone cannot be determined.  Uses 'mktime' to do the job.
+ *
+ * Results:
+ *	Returns a standard Tcl result.
+ *
+ * Side effects:
+ *	Stores an error message in the interpreter if an error occurs;
+ *	if successful, stores the 'seconds' field in 'fields.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+ConvertLocalToUTCUsingC(
+    Tcl_Interp* interp,		/* Tcl interpreter */
+    TclDateFields* fields,	/* Time to convert, with 'seconds' filled in */
+    int changeover		/* Julian Day of the Gregorian transition */
+) {
+    struct tm timeVal;
+    int localErrno;
+
+    /* Convert the given time to a date */
+
+    fields->julianDay = (int) ((fields->localSeconds + JULIAN_SEC_POSIX_EPOCH)
+			       / SECONDS_PER_DAY);
+    GetGregorianEraYearDay(fields, changeover);
+    GetMonthDay(fields);
+ 
+    /* Convert the date/time to a 'struct tm' */
+
+    timeVal.tm_year = fields->year - 1900;
+    timeVal.tm_mon = fields->month - 1;
+    timeVal.tm_mday = fields->dayOfMonth;
+    timeVal.tm_hour = (int)((fields->localSeconds / 3600) % 24);
+    timeVal.tm_min = (int)((fields->localSeconds / 60) % 60);
+    timeVal.tm_sec = (int)(fields->localSeconds % 60);
+    timeVal.tm_isdst = -1;
+    timeVal.tm_wday = -1;
+    timeVal.tm_yday = -1;
+
+    /* 
+     * Get local time. It is rumored that mktime is not thread safe
+     * on some platforms, so seize a mutex before attempting this. 
+     */
+
+    TzsetIfNecessary();
+    Tcl_MutexLock(&clockMutex);
+    errno = 0;
+    fields->seconds = (Tcl_WideInt) mktime(&timeVal);
+    localErrno = errno;
+    Tcl_MutexUnlock(&clockMutex);
+
+    /* If conversion fails, report an error */
+
+    if (localErrno != 0
+	|| (fields->seconds == -1 && timeVal.tm_yday == -1)) {
+	Tcl_SetObjResult(interp, 
+			 Tcl_NewStringObj( "time value too large/small to "
+					   "represent", -1));
 	return TCL_ERROR;
     }
-    if (Tcl_GetWideIntFromObj(interp, objv[1], &tick) != TCL_OK) {
+    return TCL_OK;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * ConvertUTCToLocal --
+ *
+ *	Converts a time (in a TclDateFields structure) from UTC to
+ *	local time.
+ *
+ * Results:
+ *	Returns a standard Tcl result.
+ *
+ * Side effects:
+ *	Populates the 'tzName' and 'tzOffset' fields.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+ConvertUTCToLocal(
+    Tcl_Interp* interp,		/* Tcl interpreter */
+    TclDateFields* fields,	/* Fields of the time */
+    Tcl_Obj* tzdata,		/* Time zone data */
+    int changeover		/* Julian Day of the Gregorian transition */
+) {
+    int rowc;			/* Number of rows in tzdata */
+    Tcl_Obj** rowv;		/* Pointers to the rows */
+
+    /* unpack the tz data */
+
+    if (Tcl_ListObjGetElements(interp, tzdata, &rowc, &rowv) != TCL_OK) {
 	return TCL_ERROR;
     }
 
-    /*
-     * Convert the time, checking for overflow
+    /* 
+     * Special case: If the time zone is :localtime, the tzdata will be empty.
+     * Use 'localtime' to convert the time to local
      */
 
-    tock = (time_t) tick;
-    if ((Tcl_WideInt) tock != tick) {
+    if (rowc == 0) {
+	return ConvertUTCToLocalUsingC(interp, fields, changeover);
+    } else {
+	return ConvertUTCToLocalUsingTable(interp, fields, rowc, rowv);
+    }
+
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * ConvertUTCToLocalUsingTable --
+ *
+ *	Converts UTC to local time, given a table of transition points
+ *
+ * Results:
+ *	Returns a standard Tcl result
+ *
+ * Side effects:
+ *	On success, fills fields->tzName, fields->tzOffset and
+ *	fields->localSeconds.  On failure, places an error message in
+ *	the interpreter result.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+ConvertUTCToLocalUsingTable(
+    Tcl_Interp* interp,		/* Tcl interpreter */
+    TclDateFields* fields,	/* Fields of the date */
+    int rowc,			/* Number of rows in the conversion table
+				 * (>= 1) */
+    Tcl_Obj *CONST rowv[]	/* Rows of the conversion table */
+) {
+
+    Tcl_Obj* row;		/* Row containing the current information */
+    int cellc;		/* Count of cells in the row (must be 4) */
+    Tcl_Obj** cellv;	/* Pointers to the cells */
+
+    /* Look up the nearest transition time */
+
+    row = LookupLastTransition(interp, fields->seconds, rowc, rowv);
+    if (row == NULL
+	|| (Tcl_ListObjGetElements(interp, row, &cellc, &cellv) != TCL_OK)
+	|| (Tcl_GetIntFromObj(interp, cellv[1], &(fields->tzOffset))
+	    != TCL_OK)) {
+	return TCL_ERROR;
+    }
+
+    /* Convert the time */
+
+    fields->tzName = cellv[3];
+    Tcl_IncrRefCount(fields->tzName);
+    fields->localSeconds = fields->seconds + fields->tzOffset;
+    return TCL_OK;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * ConvertUTCToLocalUsingC --
+ *
+ *	Converts UTC to localtime in cases where the local time zone is
+ *	not determinable, using the C 'localtime' function to do it.
+ *
+ * Results:
+ *	Returns a standard Tcl result.
+ *
+ * Side effects:
+ *	On success, fills fields->tzName, fields->tzOffset and
+ *	fields->localSeconds.  On failure, places an error message in
+ *	the interpreter result.
+ *
+ *----------------------------------------------------------------------
+ */
+ 
+static int
+ConvertUTCToLocalUsingC(
+    Tcl_Interp* interp,		/* Tcl interpreter */
+    TclDateFields* fields,	/* Time to convert, with 'seconds' filled in */
+    int changeover		/* Julian Day of the Gregorian transition */
+) {
+
+    time_t tock;
+    struct tm* timeVal;		/* Time after conversion */
+    int diff;			/* Time zone diff local-Greenwich */
+    char buffer[8];		/* Buffer for time zone name */
+
+    /* Use 'localtime' to determine local year, month, day, time of day. */
+
+    tock = (time_t) fields->seconds;
+    if ((Tcl_WideInt) tock != fields->seconds) {
 	Tcl_AppendResult(interp,
-		"number too large to represent as a Posix time", NULL);
+			 "number too large to represent as a Posix time",
+			 NULL);
 	Tcl_SetErrorCode(interp, "CLOCK", "argTooLarge", NULL);
 	return TCL_ERROR;
     }
     TzsetIfNecessary();
     timeVal = ThreadSafeLocalTime(&tock);
     if (timeVal == NULL) {
-	Tcl_AppendResult(interp, "localtime failed (clock value may be too ",
-		"large/small to represent)", NULL);
+	Tcl_AppendResult(interp,
+			 "localtime failed (clock value may be too ",
+			 "large/small to represent)", NULL);
 	Tcl_SetErrorCode(interp, "CLOCK", "localtimeFailed", NULL);
 	return TCL_ERROR;
     }
 
-    /*
-     * Package the results.
-     */
+    /* Fill in the date in 'fields' and use it to derive Julian Day */
+
+    fields->era = CE;
+    fields->year = timeVal->tm_year + 1900;
+    fields->month = timeVal->tm_mon + 1;
+    fields->dayOfMonth = timeVal->tm_mday;
+    GetJulianDayFromEraYearMonthDay(fields, changeover);
 
-    returnVec[0] = Tcl_NewIntObj(timeVal->tm_year + 1900);
-    returnVec[1] = Tcl_NewIntObj(timeVal->tm_mon + 1);
-    returnVec[2] = Tcl_NewIntObj(timeVal->tm_mday);
-    returnVec[3] = Tcl_NewIntObj(timeVal->tm_hour);
-    returnVec[4] = Tcl_NewIntObj(timeVal->tm_min);
-    returnVec[5] = Tcl_NewIntObj(timeVal->tm_sec);
-    Tcl_SetObjResult(interp, Tcl_NewListObj(6, returnVec));
+    /* Convert that value to seconds */
+    
+    fields->localSeconds = (((fields->julianDay * (Tcl_WideInt) 24
+			      + timeVal->tm_hour) * 60
+			     + timeVal->tm_min) * 60
+			    + timeVal->tm_sec) - JULIAN_SEC_POSIX_EPOCH;
+    
+    /* Determine a time zone offset and name; just use +hhmm for the name */
+
+    diff = (int) (fields->localSeconds - fields->seconds);
+    fields->tzOffset = diff;
+    if (diff < 0) {
+	*buffer = '-';
+	diff = -diff;
+    } else {
+	*buffer = '+';
+    }
+    sprintf(buffer+1, "%02d", diff / 3600);
+    diff %= 3600;
+    sprintf(buffer+3, "%02d", diff / 60);
+    diff %= 60;
+    if (diff > 0) {
+	sprintf(buffer+5, "%02d", diff);
+    }
+    fields->tzName = Tcl_NewStringObj(buffer, -1);
+    Tcl_IncrRefCount(fields->tzName);
     return TCL_OK;
 }
 
 /*
  *----------------------------------------------------------------------
  *
- * ThreadSafeLocalTime --
+ * LookupLastTransition --
  *
- *	Wrapper around the 'localtime' library function to make it thread
- *	safe.
+ *	Given a UTC time and a tzdata array, looks up the last
+ *	transition on or before the given time.
  *
  * Results:
- *	Returns a pointer to a 'struct tm' in thread-specific data.
- *
- * Side effects:
- *	Invokes localtime or localtime_r as appropriate.
+ *	Returns a pointer to the row, or NULL if an error occurs.
  *
  *----------------------------------------------------------------------
  */
 
-static struct tm *
-ThreadSafeLocalTime(
-    CONST time_t *timePtr)	/* Pointer to the number of seconds since the
-				 * local system's epoch */
+static Tcl_Obj*
+LookupLastTransition(
+    Tcl_Interp* interp,		/* Interpreter for error messages */
+    Tcl_WideInt tick,		/* Time from the epoch */
+    int rowc,			/* Number of rows of tzdata */
+    Tcl_Obj *CONST * rowv)	/* Rows in tzdata */
 {
-    /*
-     * Get a thread-local buffer to hold the returned time.
-     */
+    int l;
+    int u;
+    Tcl_Obj* compObj;
+    Tcl_WideInt compVal;
 
-    struct tm *tmPtr = (struct tm *)
-	    Tcl_GetThreadData(&tmKey, (int) sizeof(struct tm));
-#ifdef HAVE_LOCALTIME_R
-    localtime_r(timePtr, tmPtr);
-#else
-    struct tm *sysTmPtr;
+    /* Examine the first row to make sure we're in bounds */
 
-    Tcl_MutexLock(&clockMutex);
-    sysTmPtr = localtime(timePtr);
-    if (sysTmPtr == NULL) {
-	Tcl_MutexUnlock(&clockMutex);
+    if (Tcl_ListObjIndex(interp, rowv[0], 0, &compObj) != TCL_OK
+	|| Tcl_GetWideIntFromObj(interp, compObj, &compVal) != TCL_OK) {
 	return NULL;
-    } else {
-	memcpy((VOID *) tmPtr, (VOID *) localtime(timePtr), sizeof(struct tm));
-	Tcl_MutexUnlock(&clockMutex);
     }
-#endif
-    return tmPtr;
+    /* 
+     * Bizarre case - first row doesn't begin at MIN_WIDE_INT.
+     * Return it anyway. 
+     */
+    if (tick < compVal) {
+	return rowv[0];
+    }
+
+    /* 
+     * Binary-search to find the transition.
+     */
+
+    l = 0;
+    u = rowc-1;
+    while (l < u) {
+	int m = (l + u + 1) / 2;
+	if (Tcl_ListObjIndex(interp, rowv[m], 0, &compObj) != TCL_OK
+	    || Tcl_GetWideIntFromObj(interp, compObj, &compVal) != TCL_OK) {
+	    return NULL;
+	}
+	if (tick >= compVal) {
+	    l = m;
+	} else {
+	    u = m-1;
+	}
+    }
+    return rowv[l];
+    
 }
 
 /*
  *----------------------------------------------------------------------
  *
- * TclClockMktimeObjCmd --
+ * GetYearWeekDay --
  *
- *	Determine seconds from the epoch, given the fields of a local time.
+ *	Given a date with Julian Calendar Day, compute the year, week,
+ *	and day in the ISO8601 calendar.
  *
- * Usage:
- *	mktime <year> <month> <day> <hour> <minute> <second>
+ * Results:
+ *	None.
  *
- * Parameters:
- *	year -- Calendar year
- *	month -- Calendar month
- *	day -- Calendar day
- *	hour -- Hour of day (00-23)
- *	minute -- Minute of hour
- *	second -- Second of minute
+ * Side effects:
+ *	Stores 'iso8601Year', 'iso8601Week' and 'dayOfWeek' in
+ *	the date fields.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+GetYearWeekDay(
+    TclDateFields* fields,	/* Date to convert, must have 'julianDay' */
+    int changeover		/* Julian Day Number of the Gregorian
+				 * transition */
+) {
+    TclDateFields temp;
+    int dayOfFiscalYear;
+
+    /* 
+     * Find the given date, minus three days, plus one year.  That date's
+     * iso8601 year is an upper bound on the ISO8601 year of the given date.
+     */
+
+    temp.julianDay = fields->julianDay - 3;
+    GetGregorianEraYearDay(&temp, changeover);
+    if (temp.era == BCE) {
+	temp.iso8601Year = temp.year - 1;
+    } else {
+	temp.iso8601Year = temp.year + 1;
+    }
+    temp.iso8601Week = 1;
+    temp.dayOfWeek = 1;
+    GetJulianDayFromEraYearWeekDay(&temp, changeover);
+
+    /* 
+     * temp.julianDay is now the start of an ISO8601 year, either the
+     * one corresponding to the given date, or the one after. If we guessed
+     * high, move one year earlier
+     */
+
+    if (fields->julianDay < temp.julianDay) {
+	if (temp.era == BCE) {
+	    temp.iso8601Year += 1;
+	} else {
+	    temp.iso8601Year -= 1;
+	}
+	GetJulianDayFromEraYearWeekDay(&temp, changeover);
+    }
+
+    fields->iso8601Year = temp.iso8601Year;
+    dayOfFiscalYear = fields->julianDay - temp.julianDay;
+    fields->iso8601Week = (dayOfFiscalYear / 7) + 1;
+    fields->dayOfWeek = (dayOfFiscalYear + 1) % 7;
+    if (fields->dayOfWeek < 1) {
+	fields->dayOfWeek += 7;
+    }
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * GetGregorianEraYearDay --
+ *
+ *	Given a Julian Day Number, extracts the year and day of the
+ *	year and puts them into TclDateFields, along with the era
+ *	(BCE or CE) and a flag indicating whether the date is Gregorian
+ *	or Julian.
  *
  * Results:
- *	Returns the given local time.
+ *	None.
  *
- * Errors:
- *	Returns an error if the 'mktime' function does not exist in the C
- *	library, or if the given time cannot be converted.
+ * Side effects:
+ *	Stores 'era', 'gregorian', 'year', and 'dayOfYear'.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+GetGregorianEraYearDay(
+    TclDateFields* fields,	/* Date fields containing 'julianDay' */
+    int changeover		/* Gregorian transition date */
+) {
+    int jday = fields->julianDay;
+    int day;
+    int year;
+    int n;
+
+    if (jday >= changeover) {
+
+        /* Gregorian calendar */
+
+	fields->gregorian = 1;
+	year = 1;
+
+	/* 
+	 * n = Number of 400-year cycles since 1 January, 1 CE in the
+	 * proleptic Gregorian calendar.  day = remaining days.
+	 */
+
+	day = jday - JDAY_1_JAN_1_CE_GREGORIAN;
+	n = day / FOUR_CENTURIES;
+	day %= FOUR_CENTURIES;
+	year += 400 * n;
+
+	/*
+	 * n = number of centuries since the start of (year);
+	 * day = remaining days
+	 */
+
+	n = day / ONE_CENTURY_GREGORIAN;
+	day %= ONE_CENTURY_GREGORIAN;
+	if (n > 3) {
+	    /* 31 December in the last year of a 400-year cycle */
+	    n = 3;
+	    day += ONE_CENTURY_GREGORIAN;
+	}
+	year += 100 * n;
+
+    } else {
+
+	/* Julian calendar */
+
+	fields->gregorian = 0;
+	year = 1;
+	day = jday - JDAY_1_JAN_1_CE_JULIAN;
+
+    }
+
+    /* n = number of 4-year cycles; days = remaining days */
+
+    n = day / FOUR_YEARS;
+    day %= 1461;
+    year += 4 * n;
+
+    /* n = number of years; days = remaining days */
+
+    n = day / ONE_YEAR;
+    day %= ONE_YEAR;
+    if (n > 3) {
+	/* 31 December of a leap year */
+	n = 3;
+	day += 365;
+    }
+    year += n;
+
+    /* store era/year/day back into fields */
+
+    if (year < 0) {
+	fields->era = BCE;
+	fields->year = 1 - year;
+    } else {
+	fields->era = CE;
+	fields->year = year;
+    }
+    fields->dayOfYear = day + 1;
+
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * GetMonthDay --
+ *
+ *	Given a date as year and day-of-year, find month and day.
+ *
+ * Results:
+ *	None.
  *
  * Side effects:
+ *	Stores 'month' and 'dayOfMonth' in the 'fields' structure.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+GetMonthDay(
+    TclDateFields* fields	/* Date to convert */
+) {
+    int day = fields->dayOfYear;
+    int month;
+    const int* h = hath[IsGregorianLeapYear(fields)];
+    for (month = 0; month < 12 && day > h[month]; ++month) {
+	day -= h[month];
+    }
+    fields->month = month+1;
+    fields->dayOfMonth = day;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * GetJulianDayFromEraYearWeekDay --
+ *
+ *	Given a TclDateFields structure containing era, ISO8601 year,
+ *	ISO8601 week, and day of week, computes the Julian Day Number.
+ *
+ * Results:
  *	None.
  *
+ * Side effects:
+ *	Stores 'julianDay' in the fields.
+ *
  *----------------------------------------------------------------------
  */
 
-int
-TclClockMktimeObjCmd(
-    ClientData clientData,	/* Unused */
-    Tcl_Interp *interp,		/* Tcl interpreter */
-    int objc,			/* Parameter count */
-    Tcl_Obj *CONST *objv)	/* Parameter vector */
-{
-#ifndef HAVE_MKTIME
-    Tcl_AppendResult(interp, "cannot determine local time", NULL);
-    return TCL_ERROR;
-#else
+static void
+GetJulianDayFromEraYearWeekDay(
+    TclDateFields* fields,	/* Date to convert */
+    int changeover		/* Julian Day Number of the 
+				 * Gregorian transition */
+) {
 
-    int i;
-    struct tm toConvert;	/* Time to be converted */
-    time_t convertedTime;	/* Time converted from mktime */
-    int localErrno;
+    int firstMonday;		/* Julian day number of week 1, day 1
+				 * in the given year */
 
-    /*
-     * Convert parameters
-     */
+    /* Find January 4 in the ISO8601 year, which will always be in week 1 */
 
-    if (objc != 7) {
-	Tcl_WrongNumArgs(interp, 1, objv, "year month day hour minute second");
-	return TCL_ERROR;
+    TclDateFields firstWeek;
+    firstWeek.era = fields->era;
+    firstWeek.year = fields->iso8601Year;
+    firstWeek.month = 1;
+    firstWeek.dayOfMonth = 4;
+    GetJulianDayFromEraYearMonthDay(&firstWeek, changeover);
+
+    /* Find Monday of week 1. */
+
+    firstMonday = WeekdayOnOrBefore(1, firstWeek.julianDay);
+
+    /* Advance to the given week and day */
+
+    fields->julianDay = firstMonday + 7 * (fields->iso8601Week - 1)
+	+ fields->dayOfWeek - 1;
+    
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * GetJulianDayFromEraYearMonthDay --
+ *
+ *	Given era, year, month, and dayOfMonth (in TclDateFields), and
+ *	the Gregorian transition date, computes the Julian Day Number.
+ *
+ * Results:
+ *	None.
+ *
+ * Side effects:
+ *	Stores day number in 'julianDay'
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+GetJulianDayFromEraYearMonthDay(
+    TclDateFields* fields,	/* Date to convert */
+    int changeover		/* Gregorian transition date as a Julian Day */
+) {
+    int year;  int ym1;
+    int month; int mm1;
+
+    if (fields->era == BCE) {
+	year = 1 - fields->year;
+    } else {
+	year = fields->year;
     }
-    if (Tcl_GetIntFromObj(interp, objv[1], &i) != TCL_OK) {
-	return TCL_ERROR;
+
+    /* Reduce month modulo 12 */
+
+    month = fields->month;
+    mm1 = month - 1;
+    year += mm1 / 12;
+    month = (mm1 % 12) + 1;
+    ym1 = year - 1;
+    
+    /* Adjust the year after reducing the month */
+
+    fields->gregorian = 1;
+    if (year < 1) {
+	fields->era = BCE;
+	fields->year = 1-year;
+    } else {
+	fields->era = CE;
+	fields->year = year;
     }
-    toConvert.tm_year = i - 1900;
-    if (Tcl_GetIntFromObj(interp, objv[2], &i) != TCL_OK) {
-	return TCL_ERROR;
+
+    /* Try an initial conversion in the Gregorian calendar */
+
+    fields->julianDay = JDAY_1_JAN_1_CE_GREGORIAN - 1
+	+ fields->dayOfMonth
+	+ daysInPriorMonths[IsGregorianLeapYear(fields)][month - 1]
+	+ (ONE_YEAR * ym1)
+	+ (ym1 / 4)
+	- (ym1 / 100)
+	+ (ym1 / 400);
+
+    /* 
+     * If the resulting date is before the Gregorian changeover, convert
+     * in the Julian calendar instead.
+     */
+
+    if (fields->julianDay < changeover) {
+	fields->gregorian = 0;
+	fields->julianDay = JDAY_1_JAN_1_CE_JULIAN - 1
+	    + fields->dayOfMonth
+	    + daysInPriorMonths[year%4 == 0][month - 1]
+	    + (365 * ym1)
+	    + (ym1 / 4);
     }
-    toConvert.tm_mon = i - 1;
-    if (Tcl_GetIntFromObj(interp, objv[3], &i) != TCL_OK) {
-	return TCL_ERROR;
+
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * IsGregorianLeapYear --
+ *
+ *	Tests whether a given year is a leap year, in either Julian
+ *	or Gregorian calendar.
+ *
+ * Results:
+ *	Returns 1 for a leap year, 0 otherwise.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+IsGregorianLeapYear(
+    TclDateFields* fields	/* Date to test */
+) {
+    int year;
+    if (fields->era == BCE) {
+	year = 1 - fields->year;
+    } else {
+	year = fields->year;
     }
-    toConvert.tm_mday = i;
-    if (Tcl_GetIntFromObj(interp, objv[4], &i) != TCL_OK) {
-	return TCL_ERROR;
+    if (year%4 != 0) {
+	return 0;
+    } else if (!(fields->gregorian)) {
+	return 1;
+    } else if (year%400 == 0) {
+	return 1;
+    } else if (year%100 == 0) {
+	return 0;
+    } else {
+	return 1;
     }
-    toConvert.tm_hour = i;
-    if (Tcl_GetIntFromObj(interp, objv[5], &i) != TCL_OK) {
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * WeekdayOnOrBefore --
+ *
+ *	Finds the Julian Day Number of a given day of the week that
+ *	falls on or before a given date, expressed as Julian Day Number.
+ *
+ * Results:
+ *	Returns the Julian Day Number
+ *
+ *----------------------------------------------------------------------
+ */
+
+static int
+WeekdayOnOrBefore(
+    int dayOfWeek,		/* Day of week; Sunday == 0 or 7 */
+    int julianDay		/* Reference date */
+) {
+    int k = (dayOfWeek + 6) % 7;
+    return julianDay - ((julianDay - k) % 7);
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * ClockGetenvObjCmd --
+ *
+ *	Tcl command that reads an environment variable from the system
+ *
+ * Usage:
+ *	::tcl::clock::getEnv NAME
+ *
+ * Parameters:
+ *	NAME - Name of the environment variable desired
+ *
+ * Results:
+ *	Returns a standard Tcl result.  Returns an error if the
+ *	variable does not exist, with a message left in the interpreter.
+ *	Returns TCL_OK and the value of the variable if the variable
+ *	does exist,
+ *
+ *----------------------------------------------------------------------
+ */
+
+int
+ClockGetenvObjCmd(
+    ClientData clientData,
+    Tcl_Interp* interp,
+    int objc,
+    Tcl_Obj *CONST objv[])
+{
+
+    CONST char* varName;
+    CONST char* varValue;
+
+    if (objc != 2) {
+	Tcl_WrongNumArgs(interp, 1, objv, "name");
 	return TCL_ERROR;
     }
-    toConvert.tm_min = i;
-    if (Tcl_GetIntFromObj(interp, objv[6], &i) != TCL_OK) {
+    varName = Tcl_GetStringFromObj(objv[1], NULL);
+    varValue = getenv(varName);
+    if (varValue == NULL) {
+	Tcl_SetObjResult(interp,
+		Tcl_NewStringObj("variable not found", -1));
 	return TCL_ERROR;
+    } else {
+	Tcl_SetObjResult(interp, Tcl_NewStringObj(varValue, -1));
+	return TCL_OK;
     }
-    toConvert.tm_sec = i;
-    toConvert.tm_isdst = -1;
-    toConvert.tm_wday = -1;
-    toConvert.tm_yday = -1;
+}
+
+/*
+ *----------------------------------------------------------------------
+ *
+ * ThreadSafeLocalTime --
+ *
+ *	Wrapper around the 'localtime' library function to make it thread
+ *	safe.
+ *
+ * Results:
+ *	Returns a pointer to a 'struct tm' in thread-specific data.
+ *
+ * Side effects:
+ *	Invokes localtime or localtime_r as appropriate.
+ *
+ *----------------------------------------------------------------------
+ */
 
+static struct tm *
+ThreadSafeLocalTime(
+    CONST time_t *timePtr)	/* Pointer to the number of seconds since the
+				 * local system's epoch */
+{
     /*
-     * Convert the time. It is rumored that mktime is not thread safe on some
-     * platforms.
+     * Get a thread-local buffer to hold the returned time.
      */
 
-    TzsetIfNecessary();
-    Tcl_MutexLock(&clockMutex);
-    errno = 0;
-    convertedTime = mktime(&toConvert);
-    localErrno = errno;
-    Tcl_MutexUnlock(&clockMutex);
-
-    /*
-     * Return the converted time, or an error if conversion fails.
-     */
+    struct tm *tmPtr = (struct tm *)
+	    Tcl_GetThreadData(&tmKey, (int) sizeof(struct tm));
+#ifdef HAVE_LOCALTIME_R
+    localtime_r(timePtr, tmPtr);
+#else
+    struct tm *sysTmPtr;
 
-    if (localErrno != 0 || (convertedTime == -1 && toConvert.tm_yday == -1)) {
-	Tcl_AppendResult(interp, "time value too large/small to represent",
-		NULL);
-	return TCL_ERROR;
+    Tcl_MutexLock(&clockMutex);
+    sysTmPtr = localtime(timePtr);
+    if (sysTmPtr == NULL) {
+	Tcl_MutexUnlock(&clockMutex);
+	return NULL;
+    } else {
+	memcpy((VOID *) tmPtr, (VOID *) localtime(timePtr), sizeof(struct tm));
+	Tcl_MutexUnlock(&clockMutex);
     }
-
-    Tcl_SetObjResult(interp, Tcl_NewWideIntObj((Tcl_WideInt) convertedTime));
-    return TCL_OK;
-#endif /* HAVE_MKTIME */
+#endif
+    return tmPtr;
 }
 
 /*----------------------------------------------------------------------
  *
- * TclClockClicksObjCmd --
+ * ClockClicksObjCmd --
  *
  *	Returns a high-resolution counter.
  *
@@ -365,7 +1355,7 @@ TclClockMktimeObjCmd(
  */
 
 int
-TclClockClicksObjCmd(
+ClockClicksObjCmd(
     ClientData clientData,	/* Client data is unused */
     Tcl_Interp* interp,		/* Tcl interpreter */
     int objc,			/* Parameter count */
@@ -416,7 +1406,7 @@ TclClockClicksObjCmd(
 
 /*----------------------------------------------------------------------
  *
- * TclClockMillisecondsObjCmd -
+ * ClockMillisecondsObjCmd -
  *
  *	Returns a count of milliseconds since the epoch.
  *
@@ -433,7 +1423,7 @@ TclClockClicksObjCmd(
  */
 
 int
-TclClockMillisecondsObjCmd(
+ClockMillisecondsObjCmd(
     ClientData clientData,	/* Client data is unused */
     Tcl_Interp* interp,		/* Tcl interpreter */
     int objc,			/* Parameter count */
@@ -453,7 +1443,7 @@ TclClockMillisecondsObjCmd(
 
 /*----------------------------------------------------------------------
  *
- * TclClockMicrosecondsObjCmd -
+ * ClockMicrosecondsObjCmd -
  *
  *	Returns a count of microseconds since the epoch.
  *
@@ -470,7 +1460,7 @@ TclClockMillisecondsObjCmd(
  */
 
 int
-TclClockMicrosecondsObjCmd(
+ClockMicrosecondsObjCmd(
     ClientData clientData,	/* Client data is unused */
     Tcl_Interp* interp,		/* Tcl interpreter */
     int objc,			/* Parameter count */
@@ -490,7 +1480,7 @@ TclClockMicrosecondsObjCmd(
 
 /*----------------------------------------------------------------------
  *
- * TclClockSecondsObjCmd -
+ * ClockSecondsObjCmd -
  *
  *	Returns a count of microseconds since the epoch.
  *
@@ -507,7 +1497,7 @@ TclClockMicrosecondsObjCmd(
  */
 
 int
-TclClockSecondsObjCmd(
+ClockSecondsObjCmd(
     ClientData clientData,	/* Client data is unused */
     Tcl_Interp* interp,		/* Tcl interpreter */
     int objc,			/* Parameter count */
@@ -566,6 +1556,36 @@ TzsetIfNecessary(void)
 }
 
 /*
+ *----------------------------------------------------------------------
+ *
+ * ClockDeleteCmdProc --
+ *
+ *	Remove a reference to the clock client data, and clean up memory
+ *	when it's all gone.
+ *
+ * Results:
+ *	None.
+ *
+ *----------------------------------------------------------------------
+ */
+
+static void
+ClockDeleteCmdProc(ClientData clientData)
+				/* Opaque pointer to the client data */
+{
+    ClockClientData *data = (ClockClientData*) clientData;
+    int i;
+    --(data->refCount);
+    if (data->refCount == 0) {
+	for (i = 0; i < LIT__END; ++i) {
+	    Tcl_DecrRefCount(data->literals[i]);
+	}
+	ckfree((char*) (data->literals));
+	ckfree((char*) data);
+    }
+}
+
+/*
  * Local Variables:
  * mode: c
  * c-basic-offset: 4