/*  C implementation for the date/time type documented at
 *  http://www.zope.org/Members/fdrake/DateTimeWiki/FrontPage
 */

#define PY_SSIZE_T_CLEAN

#include "Python.h"
#include "modsupport.h"
#include "structmember.h"

#include <time.h>

#include "timefuncs.h"

/* Differentiate between building the core module and building extension
 * modules.
 */
#ifndef Py_BUILD_CORE
#define Py_BUILD_CORE
#endif
#include "datetime.h"
#undef Py_BUILD_CORE

/* We require that C int be at least 32 bits, and use int virtually
 * everywhere.  In just a few cases we use a temp long, where a Python
 * API returns a C long.  In such cases, we have to ensure that the
 * final result fits in a C int (this can be an issue on 64-bit boxes).
 */
#if SIZEOF_INT < 4
#	error "datetime.c requires that C int have at least 32 bits"
#endif

#define MINYEAR 1
#define MAXYEAR 9999

/* Nine decimal digits is easy to communicate, and leaves enough room
 * so that two delta days can be added w/o fear of overflowing a signed
 * 32-bit int, and with plenty of room left over to absorb any possible
 * carries from adding seconds.
 */
#define MAX_DELTA_DAYS 999999999

/* Rename the long macros in datetime.h to more reasonable short names. */
#define GET_YEAR		PyDateTime_GET_YEAR
#define GET_MONTH		PyDateTime_GET_MONTH
#define GET_DAY			PyDateTime_GET_DAY
#define DATE_GET_HOUR		PyDateTime_DATE_GET_HOUR
#define DATE_GET_MINUTE		PyDateTime_DATE_GET_MINUTE
#define DATE_GET_SECOND		PyDateTime_DATE_GET_SECOND
#define DATE_GET_MICROSECOND	PyDateTime_DATE_GET_MICROSECOND

/* Date accessors for date and datetime. */
#define SET_YEAR(o, v)		(((o)->data[0] = ((v) & 0xff00) >> 8), \
                                 ((o)->data[1] = ((v) & 0x00ff)))
#define SET_MONTH(o, v)		(PyDateTime_GET_MONTH(o) = (v))
#define SET_DAY(o, v)		(PyDateTime_GET_DAY(o) = (v))

/* Date/Time accessors for datetime. */
#define DATE_SET_HOUR(o, v)	(PyDateTime_DATE_GET_HOUR(o) = (v))
#define DATE_SET_MINUTE(o, v)	(PyDateTime_DATE_GET_MINUTE(o) = (v))
#define DATE_SET_SECOND(o, v)	(PyDateTime_DATE_GET_SECOND(o) = (v))
#define DATE_SET_MICROSECOND(o, v)	\
	(((o)->data[7] = ((v) & 0xff0000) >> 16), \
         ((o)->data[8] = ((v) & 0x00ff00) >> 8), \
         ((o)->data[9] = ((v) & 0x0000ff)))

/* Time accessors for time. */
#define TIME_GET_HOUR		PyDateTime_TIME_GET_HOUR
#define TIME_GET_MINUTE		PyDateTime_TIME_GET_MINUTE
#define TIME_GET_SECOND		PyDateTime_TIME_GET_SECOND
#define TIME_GET_MICROSECOND	PyDateTime_TIME_GET_MICROSECOND
#define TIME_SET_HOUR(o, v)	(PyDateTime_TIME_GET_HOUR(o) = (v))
#define TIME_SET_MINUTE(o, v)	(PyDateTime_TIME_GET_MINUTE(o) = (v))
#define TIME_SET_SECOND(o, v)	(PyDateTime_TIME_GET_SECOND(o) = (v))
#define TIME_SET_MICROSECOND(o, v)	\
	(((o)->data[3] = ((v) & 0xff0000) >> 16), \
         ((o)->data[4] = ((v) & 0x00ff00) >> 8), \
         ((o)->data[5] = ((v) & 0x0000ff)))

/* Delta accessors for timedelta. */
#define GET_TD_DAYS(o)		(((PyDateTime_Delta *)(o))->days)
#define GET_TD_SECONDS(o)	(((PyDateTime_Delta *)(o))->seconds)
#define GET_TD_MICROSECONDS(o)	(((PyDateTime_Delta *)(o))->microseconds)

#define SET_TD_DAYS(o, v)	((o)->days = (v))
#define SET_TD_SECONDS(o, v)	((o)->seconds = (v))
#define SET_TD_MICROSECONDS(o, v) ((o)->microseconds = (v))

/* p is a pointer to a time or a datetime object; HASTZINFO(p) returns
 * p->hastzinfo.
 */
#define HASTZINFO(p)		(((_PyDateTime_BaseTZInfo *)(p))->hastzinfo)

/* M is a char or int claiming to be a valid month.  The macro is equivalent
 * to the two-sided Python test
 *	1 <= M <= 12
 */
#define MONTH_IS_SANE(M) ((unsigned int)(M) - 1 < 12)

/* Forward declarations. */
static PyTypeObject PyDateTime_DateType;
static PyTypeObject PyDateTime_DateTimeType;
static PyTypeObject PyDateTime_DeltaType;
static PyTypeObject PyDateTime_TimeType;
static PyTypeObject PyDateTime_TZInfoType;

/* ---------------------------------------------------------------------------
 * Math utilities.
 */

/* k = i+j overflows iff k differs in sign from both inputs,
 * iff k^i has sign bit set and k^j has sign bit set,
 * iff (k^i)&(k^j) has sign bit set.
 */
#define SIGNED_ADD_OVERFLOWED(RESULT, I, J) \
	((((RESULT) ^ (I)) & ((RESULT) ^ (J))) < 0)

/* Compute Python divmod(x, y), returning the quotient and storing the
 * remainder into *r.  The quotient is the floor of x/y, and that's
 * the real point of this.  C will probably truncate instead (C99
 * requires truncation; C89 left it implementation-defined).
 * Simplification:  we *require* that y > 0 here.  That's appropriate
 * for all the uses made of it.  This simplifies the code and makes
 * the overflow case impossible (divmod(LONG_MIN, -1) is the only
 * overflow case).
 */
static int
divmod(int x, int y, int *r)
{
	int quo;

	assert(y > 0);
	quo = x / y;
	*r = x - quo * y;
	if (*r < 0) {
		--quo;
		*r += y;
	}
	assert(0 <= *r && *r < y);
	return quo;
}

/* Round a double to the nearest long.  |x| must be small enough to fit
 * in a C long; this is not checked.
 */
static long
round_to_long(double x)
{
	if (x >= 0.0)
		x = floor(x + 0.5);
	else
		x = ceil(x - 0.5);
	return (long)x;
}

/* ---------------------------------------------------------------------------
 * General calendrical helper functions
 */

/* For each month ordinal in 1..12, the number of days in that month,
 * and the number of days before that month in the same year.  These
 * are correct for non-leap years only.
 */
static int _days_in_month[] = {
	0, /* unused; this vector uses 1-based indexing */
	31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
};

static int _days_before_month[] = {
	0, /* unused; this vector uses 1-based indexing */
	0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334
};

/* year -> 1 if leap year, else 0. */
static int
is_leap(int year)
{
	/* Cast year to unsigned.  The result is the same either way, but
	 * C can generate faster code for unsigned mod than for signed
	 * mod (especially for % 4 -- a good compiler should just grab
	 * the last 2 bits when the LHS is unsigned).
	 */
	const unsigned int ayear = (unsigned int)year;
	return ayear % 4 == 0 && (ayear % 100 != 0 || ayear % 400 == 0);
}

/* year, month -> number of days in that month in that year */
static int
days_in_month(int year, int month)
{
	assert(month >= 1);
	assert(month <= 12);
	if (month == 2 && is_leap(year))
		return 29;
	else
		return _days_in_month[month];
}

/* year, month -> number of days in year preceeding first day of month */
static int
days_before_month(int year, int month)
{
	int days;

	assert(month >= 1);
	assert(month <= 12);
	days = _days_before_month[month];
	if (month > 2 && is_leap(year))
		++days;
	return days;
}

/* year -> number of days before January 1st of year.  Remember that we
 * start with year 1, so days_before_year(1) == 0.
 */
static int
days_before_year(int year)
{
	int y = year - 1;
	/* This is incorrect if year <= 0; we really want the floor
	 * here.  But so long as MINYEAR is 1, the smallest year this
	 * can see is 0 (this can happen in some normalization endcases),
	 * so we'll just special-case that.
	 */
	assert (year >= 0);
	if (y >= 0)
		return y*365 + y/4 - y/100 + y/400;
	else {
		assert(y == -1);
		return -366;
	}
}

/* Number of days in 4, 100, and 400 year cycles.  That these have
 * the correct values is asserted in the module init function.
 */
#define DI4Y	1461	/* days_before_year(5); days in 4 years */
#define DI100Y	36524	/* days_before_year(101); days in 100 years */
#define DI400Y	146097	/* days_before_year(401); days in 400 years  */

/* ordinal -> year, month, day, considering 01-Jan-0001 as day 1. */
static void
ord_to_ymd(int ordinal, int *year, int *month, int *day)
{
	int n, n1, n4, n100, n400, leapyear, preceding;

	/* ordinal is a 1-based index, starting at 1-Jan-1.  The pattern of
	 * leap years repeats exactly every 400 years.  The basic strategy is
	 * to find the closest 400-year boundary at or before ordinal, then
	 * work with the offset from that boundary to ordinal.  Life is much
	 * clearer if we subtract 1 from ordinal first -- then the values
	 * of ordinal at 400-year boundaries are exactly those divisible
	 * by DI400Y:
	 *
	 *    D  M   Y            n              n-1
	 *    -- --- ----        ----------     ----------------
	 *    31 Dec -400        -DI400Y       -DI400Y -1
	 *     1 Jan -399         -DI400Y +1   -DI400Y      400-year boundary
	 *    ...
	 *    30 Dec  000        -1             -2
	 *    31 Dec  000         0             -1
	 *     1 Jan  001         1              0          400-year boundary
	 *     2 Jan  001         2              1
	 *     3 Jan  001         3              2
	 *    ...
	 *    31 Dec  400         DI400Y        DI400Y -1
	 *     1 Jan  401         DI400Y +1     DI400Y      400-year boundary
	 */
	assert(ordinal >= 1);
	--ordinal;
	n400 = ordinal / DI400Y;
	n = ordinal % DI400Y;
	*year = n400 * 400 + 1;

	/* Now n is the (non-negative) offset, in days, from January 1 of
	 * year, to the desired date.  Now compute how many 100-year cycles
	 * precede n.
	 * Note that it's possible for n100 to equal 4!  In that case 4 full
	 * 100-year cycles precede the desired day, which implies the
	 * desired day is December 31 at the end of a 400-year cycle.
	 */
	n100 = n / DI100Y;
	n = n % DI100Y;

	/* Now compute how many 4-year cycles precede it. */
	n4 = n / DI4Y;
	n = n % DI4Y;

	/* And now how many single years.  Again n1 can be 4, and again
	 * meaning that the desired day is December 31 at the end of the
	 * 4-year cycle.
	 */
	n1 = n / 365;
	n = n % 365;

	*year += n100 * 100 + n4 * 4 + n1;
	if (n1 == 4 || n100 == 4) {
		assert(n == 0);
		*year -= 1;
		*month = 12;
		*day = 31;
		return;
	}

	/* Now the year is correct, and n is the offset from January 1.  We
	 * find the month via an estimate that's either exact or one too
	 * large.
	 */
	leapyear = n1 == 3 && (n4 != 24 || n100 == 3);
	assert(leapyear == is_leap(*year));
	*month = (n + 50) >> 5;
	preceding = (_days_before_month[*month] + (*month > 2 && leapyear));
	if (preceding > n) {
		/* estimate is too large */
		*month -= 1;
		preceding -= days_in_month(*year, *month);
	}
	n -= preceding;
	assert(0 <= n);
	assert(n < days_in_month(*year, *month));

	*day = n + 1;
}

/* year, month, day -> ordinal, considering 01-Jan-0001 as day 1. */
static int
ymd_to_ord(int year, int month, int day)
{
	return days_before_year(year) + days_before_month(year, month) + day;
}

/* Day of week, where Monday==0, ..., Sunday==6.  1/1/1 was a Monday. */
static int
weekday(int year, int month, int day)
{
	return (ymd_to_ord(year, month, day) + 6) % 7;
}

/* Ordinal of the Monday starting week 1 of the ISO year.  Week 1 is the
 * first calendar week containing a Thursday.
 */
static int
iso_week1_monday(int year)
{
	int first_day = ymd_to_ord(year, 1, 1);	/* ord of 1/1 */
	/* 0 if 1/1 is a Monday, 1 if a Tue, etc. */
	int first_weekday = (first_day + 6) % 7;
	/* ordinal of closest Monday at or before 1/1 */
	int week1_monday  = first_day - first_weekday;

	if (first_weekday > 3)	/* if 1/1 was Fri, Sat, Sun */
		week1_monday += 7;
	return week1_monday;
}

/* ---------------------------------------------------------------------------
 * Range checkers.
 */

/* Check that -MAX_DELTA_DAYS <= days <= MAX_DELTA_DAYS.  If so, return 0.
 * If not, raise OverflowError and return -1.
 */
static int
check_delta_day_range(int days)
{
	if (-MAX_DELTA_DAYS <= days && days <= MAX_DELTA_DAYS)
		return 0;
	PyErr_Format(PyExc_OverflowError,
		     "days=%d; must have magnitude <= %d",
		     days, MAX_DELTA_DAYS);
	return -1;
}

/* Check that date arguments are in range.  Return 0 if they are.  If they
 * aren't, raise ValueError and return -1.
 */
static int
check_date_args(int year, int month, int day)
{

	if (year < MINYEAR || year > MAXYEAR) {
		PyErr_SetString(PyExc_ValueError,
				"year is out of range");
		return -1;
	}
	if (month < 1 || month > 12) {
		PyErr_SetString(PyExc_ValueError,
				"month must be in 1..12");
		return -1;
	}
	if (day < 1 || day > days_in_month(year, month)) {
		PyErr_SetString(PyExc_ValueError,
				"day is out of range for month");
		return -1;
	}
	return 0;
}

/* Check that time arguments are in range.  Return 0 if they are.  If they
 * aren't, raise ValueError and return -1.
 */
static int
check_time_args(int h, int m, int s, int us)
{
	if (h < 0 || h > 23) {
		PyErr_SetString(PyExc_ValueError,
				"hour must be in 0..23");
		return -1;
	}
	if (m < 0 || m > 59) {
		PyErr_SetString(PyExc_ValueError,
				"minute must be in 0..59");
		return -1;
	}
	if (s < 0 || s > 59) {
		PyErr_SetString(PyExc_ValueError,
				"second must be in 0..59");
		return -1;
	}
	if (us < 0 || us > 999999) {
		PyErr_SetString(PyExc_ValueError,
				"microsecond must be in 0..999999");
		return -1;
	}
	return 0;
}

/* ---------------------------------------------------------------------------
 * Normalization utilities.
 */

/* One step of a mixed-radix conversion.  A "hi" unit is equivalent to
 * factor "lo" units.  factor must be > 0.  If *lo is less than 0, or
 * at least factor, enough of *lo is converted into "hi" units so that
 * 0 <= *lo < factor.  The input values must be such that int overflow
 * is impossible.
 */
static void
normalize_pair(int *hi, int *lo, int factor)
{
	assert(factor > 0);
	assert(lo != hi);
	if (*lo < 0 || *lo >= factor) {
		const int num_hi = divmod(*lo, factor, lo);
		const int new_hi = *hi + num_hi;
		assert(! SIGNED_ADD_OVERFLOWED(new_hi, *hi, num_hi));
		*hi = new_hi;
	}
	assert(0 <= *lo && *lo < factor);
}

/* Fiddle days (d), seconds (s), and microseconds (us) so that
 * 	0 <= *s < 24*3600
 * 	0 <= *us < 1000000
 * The input values must be such that the internals don't overflow.
 * The way this routine is used, we don't get close.
 */
static void
normalize_d_s_us(int *d, int *s, int *us)
{
	if (*us < 0 || *us >= 1000000) {
		normalize_pair(s, us, 1000000);
		/* |s| can't be bigger than about
		 * |original s| + |original us|/1000000 now.
		 */

	}
	if (*s < 0 || *s >= 24*3600) {
		normalize_pair(d, s, 24*3600);
		/* |d| can't be bigger than about
		 * |original d| +
		 * (|original s| + |original us|/1000000) / (24*3600) now.
		 */
	}
	assert(0 <= *s && *s < 24*3600);
	assert(0 <= *us && *us < 1000000);
}

/* Fiddle years (y), months (m), and days (d) so that
 * 	1 <= *m <= 12
 * 	1 <= *d <= days_in_month(*y, *m)
 * The input values must be such that the internals don't overflow.
 * The way this routine is used, we don't get close.
 */
static void
normalize_y_m_d(int *y, int *m, int *d)
{
	int dim;	/* # of days in month */

	/* This gets muddy:  the proper range for day can't be determined
	 * without knowing the correct month and year, but if day is, e.g.,
	 * plus or minus a million, the current month and year values make
	 * no sense (and may also be out of bounds themselves).
	 * Saying 12 months == 1 year should be non-controversial.
	 */
	if (*m < 1 || *m > 12) {
		--*m;
		normalize_pair(y, m, 12);
		++*m;
		/* |y| can't be bigger than about
		 * |original y| + |original m|/12 now.
		 */
	}
	assert(1 <= *m && *m <= 12);

	/* Now only day can be out of bounds (year may also be out of bounds
	 * for a datetime object, but we don't care about that here).
	 * If day is out of bounds, what to do is arguable, but at least the
	 * method here is principled and explainable.
	 */
	dim = days_in_month(*y, *m);
	if (*d < 1 || *d > dim) {
		/* Move day-1 days from the first of the month.  First try to
		 * get off cheap if we're only one day out of range
		 * (adjustments for timezone alone can't be worse than that).
		 */
		if (*d == 0) {
			--*m;
			if (*m > 0)
				*d = days_in_month(*y, *m);
			else {
				--*y;
				*m = 12;
				*d = 31;
			}
		}
		else if (*d == dim + 1) {
			/* move forward a day */
			++*m;
			*d = 1;
			if (*m > 12) {
				*m = 1;
				++*y;
			}
		}
		else {
			int ordinal = ymd_to_ord(*y, *m, 1) +
						  *d - 1;
			ord_to_ymd(ordinal, y, m, d);
		}
	}
	assert(*m > 0);
	assert(*d > 0);
}

/* Fiddle out-of-bounds months and days so that the result makes some kind
 * of sense.  The parameters are both inputs and outputs.  Returns < 0 on
 * failure, where failure means the adjusted year is out of bounds.
 */
static int
normalize_date(int *year, int *month, int *day)
{
	int result;

	normalize_y_m_d(year, month, day);
	if (MINYEAR <= *year && *year <= MAXYEAR)
		result = 0;
	else {
		PyErr_SetString(PyExc_OverflowError,
				"date value out of range");
		result = -1;
	}
	return result;
}

/* Force all the datetime fields into range.  The parameters are both
 * inputs and outputs.  Returns < 0 on error.
 */
static int
normalize_datetime(int *year, int *month, int *day,
                   int *hour, int *minute, int *second,
                   int *microsecond)
{
	normalize_pair(second, microsecond, 1000000);
	normalize_pair(minute, second, 60);
	normalize_pair(hour, minute, 60);
	normalize_pair(day, hour, 24);
	return normalize_date(year, month, day);
}

/* ---------------------------------------------------------------------------
 * Basic object allocation:  tp_alloc implementations.  These allocate
 * Python objects of the right size and type, and do the Python object-
 * initialization bit.  If there's not enough memory, they return NULL after
 * setting MemoryError.  All data members remain uninitialized trash.
 *
 * We abuse the tp_alloc "nitems" argument to communicate whether a tzinfo
 * member is needed.  This is ugly, imprecise, and possibly insecure.
 * tp_basicsize for the time and datetime types is set to the size of the
 * struct that has room for the tzinfo member, so subclasses in Python will
 * allocate enough space for a tzinfo member whether or not one is actually
 * needed.  That's the "ugly and imprecise" parts.  The "possibly insecure"
 * part is that PyType_GenericAlloc() (which subclasses in Python end up
 * using) just happens today to effectively ignore the nitems argument
 * when tp_itemsize is 0, which it is for these type objects.  If that
 * changes, perhaps the callers of tp_alloc slots in this file should
 * be changed to force a 0 nitems argument unless the type being allocated
 * is a base type implemented in this file (so that tp_alloc is time_alloc
 * or datetime_alloc below, which know about the nitems abuse).
 */

static PyObject *
time_alloc(PyTypeObject *type, Py_ssize_t aware)
{
	PyObject *self;

	self = (PyObject *)
		PyObject_MALLOC(aware ?
				sizeof(PyDateTime_Time) :
				sizeof(_PyDateTime_BaseTime));
	if (self == NULL)
		return (PyObject *)PyErr_NoMemory();
	PyObject_INIT(self, type);
	return self;
}

static PyObject *
datetime_alloc(PyTypeObject *type, Py_ssize_t aware)
{
	PyObject *self;

	self = (PyObject *)
		PyObject_MALLOC(aware ?
				sizeof(PyDateTime_DateTime) :
				sizeof(_PyDateTime_BaseDateTime));
	if (self == NULL)
		return (PyObject *)PyErr_NoMemory();
	PyObject_INIT(self, type);
	return self;
}

/* ---------------------------------------------------------------------------
 * Helpers for setting object fields.  These work on pointers to the
 * appropriate base class.
 */

/* For date and datetime. */
static void
set_date_fields(PyDateTime_Date *self, int y, int m, int d)
{
	self->hashcode = -1;
	SET_YEAR(self, y);
	SET_MONTH(self, m);
	SET_DAY(self, d);
}

/* ---------------------------------------------------------------------------
 * Create various objects, mostly without range checking.
 */

/* Create a date instance with no range checking. */
static PyObject *
new_date_ex(int year, int month, int day, PyTypeObject *type)
{
	PyDateTime_Date *self;

	self = (PyDateTime_Date *) (type->tp_alloc(type, 0));
	if (self != NULL)
		set_date_fields(self, year, month, day);
	return (PyObject *) self;
}

#define new_date(year, month, day) \
	new_date_ex(year, month, day, &PyDateTime_DateType)

/* Create a datetime instance with no range checking. */
static PyObject *
new_datetime_ex(int year, int month, int day, int hour, int minute,
	     int second, int usecond, PyObject *tzinfo, PyTypeObject *type)
{
	PyDateTime_DateTime *self;
	char aware = tzinfo != Py_None;

	self = (PyDateTime_DateTime *) (type->tp_alloc(type, aware));
	if (self != NULL) {
		self->hastzinfo = aware;
		set_date_fields((PyDateTime_Date *)self, year, month, day);
		DATE_SET_HOUR(self, hour);
		DATE_SET_MINUTE(self, minute);
		DATE_SET_SECOND(self, second);
		DATE_SET_MICROSECOND(self, usecond);
		if (aware) {
			Py_INCREF(tzinfo);
			self->tzinfo = tzinfo;
		}
	}
	return (PyObject *)self;
}

#define new_datetime(y, m, d, hh, mm, ss, us, tzinfo)		\
	new_datetime_ex(y, m, d, hh, mm, ss, us, tzinfo,	\
			&PyDateTime_DateTimeType)

/* Create a time instance with no range checking. */
static PyObject *
new_time_ex(int hour, int minute, int second, int usecond,
	    PyObject *tzinfo, PyTypeObject *type)
{
	PyDateTime_Time *self;
	char aware = tzinfo != Py_None;

	self = (PyDateTime_Time *) (type->tp_alloc(type, aware));
	if (self != NULL) {
		self->hastzinfo = aware;
		self->hashcode = -1;
		TIME_SET_HOUR(self, hour);
		TIME_SET_MINUTE(self, minute);
		TIME_SET_SECOND(self, second);
		TIME_SET_MICROSECOND(self, usecond);
		if (aware) {
			Py_INCREF(tzinfo);
			self->tzinfo = tzinfo;
		}
	}
	return (PyObject *)self;
}

#define new_time(hh, mm, ss, us, tzinfo)		\
	new_time_ex(hh, mm, ss, us, tzinfo, &PyDateTime_TimeType)

/* Create a timedelta instance.  Normalize the members iff normalize is
 * true.  Passing false is a speed optimization, if you know for sure
 * that seconds and microseconds are already in their proper ranges.  In any
 * case, raises OverflowError and returns NULL if the normalized days is out
 * of range).
 */
static PyObject *
new_delta_ex(int days, int seconds, int microseconds, int normalize,
	     PyTypeObject *type)
{
	PyDateTime_Delta *self;

	if (normalize)
		normalize_d_s_us(&days, &seconds, &microseconds);
	assert(0 <= seconds && seconds < 24*3600);
	assert(0 <= microseconds && microseconds < 1000000);

 	if (check_delta_day_range(days) < 0)
 		return NULL;

	self = (PyDateTime_Delta *) (type->tp_alloc(type, 0));
	if (self != NULL) {
		self->hashcode = -1;
		SET_TD_DAYS(self, days);
		SET_TD_SECONDS(self, seconds);
		SET_TD_MICROSECONDS(self, microseconds);
	}
	return (PyObject *) self;
}

#define new_delta(d, s, us, normalize)	\
	new_delta_ex(d, s, us, normalize, &PyDateTime_DeltaType)

/* ---------------------------------------------------------------------------
 * tzinfo helpers.
 */

/* Ensure that p is None or of a tzinfo subclass.  Return 0 if OK; if not
 * raise TypeError and return -1.
 */
static int
check_tzinfo_subclass(PyObject *p)
{
	if (p == Py_None || PyTZInfo_Check(p))
		return 0;
	PyErr_Format(PyExc_TypeError,
		     "tzinfo argument must be None or of a tzinfo subclass, "
		     "not type '%s'",
		     Py_TYPE(p)->tp_name);
	return -1;
}

/* Return tzinfo.methname(tzinfoarg), without any checking of results.
 * If tzinfo is None, returns None.
 */
static PyObject *
call_tzinfo_method(PyObject *tzinfo, char *methname, PyObject *tzinfoarg)
{
	PyObject *result;

	assert(tzinfo && methname && tzinfoarg);
	assert(check_tzinfo_subclass(tzinfo) >= 0);
	if (tzinfo == Py_None) {
		result = Py_None;
		Py_INCREF(result);
	}
	else
		result = PyObject_CallMethod(tzinfo, methname, "O", tzinfoarg);
	return result;
}

/* If self has a tzinfo member, return a BORROWED reference to it.  Else
 * return NULL, which is NOT AN ERROR.  There are no error returns here,
 * and the caller must not decref the result.
 */
static PyObject *
get_tzinfo_member(PyObject *self)
{
	PyObject *tzinfo = NULL;

	if (PyDateTime_Check(self) && HASTZINFO(self))
		tzinfo = ((PyDateTime_DateTime *)self)->tzinfo;
	else if (PyTime_Check(self) && HASTZINFO(self))
		tzinfo = ((PyDateTime_Time *)self)->tzinfo;

	return tzinfo;
}

/* Call getattr(tzinfo, name)(tzinfoarg), and extract an int from the
 * result.  tzinfo must be an instance of the tzinfo class.  If the method
 * returns None, this returns 0 and sets *none to 1.  If the method doesn't
 * return None or timedelta, TypeError is raised and this returns -1.  If it
 * returnsa timedelta and the value is out of range or isn't a whole number
 * of minutes, ValueError is raised and this returns -1.
 * Else *none is set to 0 and the integer method result is returned.
 */
static int
call_utc_tzinfo_method(PyObject *tzinfo, char *name, PyObject *tzinfoarg,
		       int *none)
{
	PyObject *u;
	int result = -1;

	assert(tzinfo != NULL);
	assert(PyTZInfo_Check(tzinfo));
	assert(tzinfoarg != NULL);

	*none = 0;
	u = call_tzinfo_method(tzinfo, name, tzinfoarg);
	if (u == NULL)
		return -1;

	else if (u == Py_None) {
		result = 0;
		*none = 1;
	}
	else if (PyDelta_Check(u)) {
		const int days = GET_TD_DAYS(u);
		if (days < -1 || days > 0)
			result = 24*60;	/* trigger ValueError below */
		else {
			/* next line can't overflow because we know days
			 * is -1 or 0 now
			 */
			int ss = days * 24 * 3600 + GET_TD_SECONDS(u);
			result = divmod(ss, 60, &ss);
			if (ss || GET_TD_MICROSECONDS(u)) {
				PyErr_Format(PyExc_ValueError,
					     "tzinfo.%s() must return a "
					     "whole number of minutes",
					     name);
				result = -1;
			}
		}
	}
	else {
		PyErr_Format(PyExc_TypeError,
			     "tzinfo.%s() must return None or "
			     "timedelta, not '%s'",
			     name, Py_TYPE(u)->tp_name);
	}

	Py_DECREF(u);
	if (result < -1439 || result > 1439) {
		PyErr_Format(PyExc_ValueError,
			     "tzinfo.%s() returned %d; must be in "
			     "-1439 .. 1439",
			     name, result);
		result = -1;
	}
	return result;
}

/* Call tzinfo.utcoffset(tzinfoarg), and extract an integer from the
 * result.  tzinfo must be an instance of the tzinfo class.  If utcoffset()
 * returns None, call_utcoffset returns 0 and sets *none to 1.  If uctoffset()
 * doesn't return None or timedelta, TypeError is raised and this returns -1.
 * If utcoffset() returns an invalid timedelta (out of range, or not a whole
 * # of minutes), ValueError is raised and this returns -1.  Else *none is
 * set to 0 and the offset is returned (as int # of minutes east of UTC).
 */
static int
call_utcoffset(PyObject *tzinfo, PyObject *tzinfoarg, int *none)
{
	return call_utc_tzinfo_method(tzinfo, "utcoffset", tzinfoarg, none);
}

/* Call tzinfo.name(tzinfoarg), and return the offset as a timedelta or None.
 */
static PyObject *
offset_as_timedelta(PyObject *tzinfo, char *name, PyObject *tzinfoarg) {
	PyObject *result;

	assert(tzinfo && name && tzinfoarg);
	if (tzinfo == Py_None) {
		result = Py_None;
		Py_INCREF(result);
	}
	else {
		int none;
		int offset = call_utc_tzinfo_method(tzinfo, name, tzinfoarg,
						    &none);
		if (offset < 0 && PyErr_Occurred())
			return NULL;
		if (none) {
			result = Py_None;
			Py_INCREF(result);
		}
		else
			result = new_delta(0, offset * 60, 0, 1);
	}
	return result;
}

/* Call tzinfo.dst(tzinfoarg), and extract an integer from the
 * result.  tzinfo must be an instance of the tzinfo class.  If dst()
 * returns None, call_dst returns 0 and sets *none to 1.  If dst()
 & doesn't return None or timedelta, TypeError is raised and this
 * returns -1.  If dst() returns an invalid timedelta for a UTC offset,
 * ValueError is raised and this returns -1.  Else *none is set to 0 and
 * the offset is returned (as an int # of minutes east of UTC).
 */
static int
call_dst(PyObject *tzinfo, PyObject *tzinfoarg, int *none)
{
	return call_utc_tzinfo_method(tzinfo, "dst", tzinfoarg, none);
}

/* Call tzinfo.tzname(tzinfoarg), and return the result.  tzinfo must be
 * an instance of the tzinfo class or None.  If tzinfo isn't None, and
 * tzname() doesn't return None or a string, TypeError is raised and this
 * returns NULL.
 */
static PyObject *
call_tzname(PyObject *tzinfo, PyObject *tzinfoarg)
{
	PyObject *result;

	assert(tzinfo != NULL);
	assert(check_tzinfo_subclass(tzinfo) >= 0);
	assert(tzinfoarg != NULL);

	if (tzinfo == Py_None) {
		result = Py_None;
		Py_INCREF(result);
	}
	else
		result = PyObject_CallMethod(tzinfo, "tzname", "O", tzinfoarg);

	if (result != NULL && result != Py_None && ! PyString_Check(result)) {
		PyErr_Format(PyExc_TypeError, "tzinfo.tzname() must "
			     "return None or a string, not '%s'",
			     Py_TYPE(result)->tp_name);
		Py_DECREF(result);
		result = NULL;
	}
	return result;
}

typedef enum {
	      /* an exception has been set; the caller should pass it on */
	      OFFSET_ERROR,

	      /* type isn't date, datetime, or time subclass */
	      OFFSET_UNKNOWN,

	      /* date,
	       * datetime with !hastzinfo
	       * datetime with None tzinfo,
	       * datetime where utcoffset() returns None
	       * time with !hastzinfo
	       * time with None tzinfo,
	       * time where utcoffset() returns None
	       */
	      OFFSET_NAIVE,

	      /* time or datetime where utcoffset() doesn't return None */
	      OFFSET_AWARE
} naivety;

/* Classify an object as to whether it's naive or offset-aware.  See
 * the "naivety" typedef for details.  If the type is aware, *offset is set
 * to minutes east of UTC (as returned by the tzinfo.utcoffset() method).
 * If the type is offset-naive (or unknown, or error), *offset is set to 0.
 * tzinfoarg is the argument to pass to the tzinfo.utcoffset() method.
 */
static naivety
classify_utcoffset(PyObject *op, PyObject *tzinfoarg, int *offset)
{
	int none;
	PyObject *tzinfo;

	assert(tzinfoarg != NULL);
	*offset = 0;
	tzinfo = get_tzinfo_member(op);	/* NULL means no tzinfo, not error */
	if (tzinfo == Py_None)
		return OFFSET_NAIVE;
	if (tzinfo == NULL) {
		/* note that a datetime passes the PyDate_Check test */
		return (PyTime_Check(op) || PyDate_Check(op)) ?
		       OFFSET_NAIVE : OFFSET_UNKNOWN;
	}
	*offset = call_utcoffset(tzinfo, tzinfoarg, &none);
	if (*offset == -1 && PyErr_Occurred())
		return OFFSET_ERROR;
	return none ? OFFSET_NAIVE : OFFSET_AWARE;
}

/* Classify two objects as to whether they're naive or offset-aware.
 * This isn't quite the same as calling classify_utcoffset() twice:  for
 * binary operations (comparison and subtraction), we generally want to
 * ignore the tzinfo members if they're identical.  This is by design,
 * so that results match "naive" expectations when mixing objects from a
 * single timezone.  So in that case, this sets both offsets to 0 and
 * both naiveties to OFFSET_NAIVE.
 * The function returns 0 if everything's OK, and -1 on error.
 */
static int
classify_two_utcoffsets(PyObject *o1, int *offset1, naivety *n1,
			PyObject *tzinfoarg1,
			PyObject *o2, int *offset2, naivety *n2,
			PyObject *tzinfoarg2)
{
	if (get_tzinfo_member(o1) == get_tzinfo_member(o2)) {
		*offset1 = *offset2 = 0;
		*n1 = *n2 = OFFSET_NAIVE;
	}
	else {
		*n1 = classify_utcoffset(o1, tzinfoarg1, offset1);
		if (*n1 == OFFSET_ERROR)
			return -1;
		*n2 = classify_utcoffset(o2, tzinfoarg2, offset2);
		if (*n2 == OFFSET_ERROR)
			return -1;
	}
	return 0;
}

/* repr is like "someclass(arg1, arg2)".  If tzinfo isn't None,
 * stuff
 *     ", tzinfo=" + repr(tzinfo)
 * before the closing ")".
 */
static PyObject *
append_keyword_tzinfo(PyObject *repr, PyObject *tzinfo)
{
	PyObject *temp;

	assert(PyString_Check(repr));
	assert(tzinfo);
	if (tzinfo == Py_None)
		return repr;
	/* Get rid of the trailing ')'. */
	assert(PyString_AsString(repr)[PyString_Size(repr)-1] == ')');
	temp = PyString_FromStringAndSize(PyString_AsString(repr),
					  PyString_Size(repr) - 1);
	Py_DECREF(repr);
	if (temp == NULL)
		return NULL;
	repr = temp;

	/* Append ", tzinfo=". */
	PyString_ConcatAndDel(&repr, PyString_FromString(", tzinfo="));

	/* Append repr(tzinfo). */
	PyString_ConcatAndDel(&repr, PyObject_Repr(tzinfo));

	/* Add a closing paren. */
	PyString_ConcatAndDel(&repr, PyString_FromString(")"));
	return repr;
}

/* ---------------------------------------------------------------------------
 * String format helpers.
 */

static PyObject *
format_ctime(PyDateTime_Date *date, int hours, int minutes, int seconds)
{
	static const char *DayNames[] = {
		"Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"
	};
	static const char *MonthNames[] = {
		"Jan", "Feb", "Mar", "Apr", "May", "Jun",
		"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
	};

	char buffer[128];
	int wday = weekday(GET_YEAR(date), GET_MONTH(date), GET_DAY(date));

	PyOS_snprintf(buffer, sizeof(buffer), "%s %s %2d %02d:%02d:%02d %04d",
		      DayNames[wday], MonthNames[GET_MONTH(date) - 1],
		      GET_DAY(date), hours, minutes, seconds,
		      GET_YEAR(date));
	return PyString_FromString(buffer);
}

/* Add an hours & minutes UTC offset string to buf.  buf has no more than
 * buflen bytes remaining.  The UTC offset is gotten by calling
 * tzinfo.uctoffset(tzinfoarg).  If that returns None, \0 is stored into
 * *buf, and that's all.  Else the returned value is checked for sanity (an
 * integer in range), and if that's OK it's converted to an hours & minutes
 * string of the form
 *   sign HH sep MM
 * Returns 0 if everything is OK.  If the return value from utcoffset() is
 * bogus, an appropriate exception is set and -1 is returned.
 */
static int
format_utcoffset(char *buf, size_t buflen, const char *sep,
		PyObject *tzinfo, PyObject *tzinfoarg)
{
	int offset;
	int hours;
	int minutes;
	char sign;
	int none;

	assert(buflen >= 1);

	offset = call_utcoffset(tzinfo, tzinfoarg, &none);
	if (offset == -1 && PyErr_Occurred())
		return -1;
	if (none) {
		*buf = '\0';
		return 0;
	}
	sign = '+';
	if (offset < 0) {
		sign = '-';
		offset = - offset;
	}
	hours = divmod(offset, 60, &minutes);
	PyOS_snprintf(buf, buflen, "%c%02d%s%02d", sign, hours, sep, minutes);
	return 0;
}

static PyObject *
make_freplacement(PyObject *object)
{
	char freplacement[64];
	if (PyTime_Check(object))
	    sprintf(freplacement, "%06d", TIME_GET_MICROSECOND(object));
	else if (PyDateTime_Check(object))
	    sprintf(freplacement, "%06d", DATE_GET_MICROSECOND(object));
	else
	    sprintf(freplacement, "%06d", 0);

	return PyString_FromStringAndSize(freplacement, strlen(freplacement));
}

/* I sure don't want to reproduce the strftime code from the time module,
 * so this imports the module and calls it.  All the hair is due to
 * giving special meanings to the %z, %Z and %f format codes via a
 * preprocessing step on the format string.
 * tzinfoarg is the argument to pass to the object's tzinfo method, if
 * needed.
 */
static PyObject *
wrap_strftime(PyObject *object, const char *format, size_t format_len,
		PyObject *timetuple, PyObject *tzinfoarg)
{
	PyObject *result = NULL;	/* guilty until proved innocent */

	PyObject *zreplacement = NULL;	/* py string, replacement for %z */
	PyObject *Zreplacement = NULL;	/* py string, replacement for %Z */
	PyObject *freplacement = NULL;	/* py string, replacement for %f */

	const char *pin;	/* pointer to next char in input format */
	char ch;		/* next char in input format */

	PyObject *newfmt = NULL;	/* py string, the output format */
	char *pnew;	/* pointer to available byte in output format */
	size_t totalnew;	/* number bytes total in output format buffer,
				   exclusive of trailing \0 */
	size_t usednew;	/* number bytes used so far in output format buffer */

	const char *ptoappend;	/* ptr to string to append to output buffer */
	size_t ntoappend;	/* # of bytes to append to output buffer */

	assert(object && format && timetuple);

	/* Give up if the year is before 1900.
	 * Python strftime() plays games with the year, and different
	 * games depending on whether envar PYTHON2K is set.  This makes
	 * years before 1900 a nightmare, even if the platform strftime
	 * supports them (and not all do).
	 * We could get a lot farther here by avoiding Python's strftime
	 * wrapper and calling the C strftime() directly, but that isn't
	 * an option in the Python implementation of this module.
	 */
	{
		long year;
		PyObject *pyyear = PySequence_GetItem(timetuple, 0);
		if (pyyear == NULL) return NULL;
		assert(PyInt_Check(pyyear));
		year = PyInt_AsLong(pyyear);
		Py_DECREF(pyyear);
		if (year < 1900) {
			PyErr_Format(PyExc_ValueError, "year=%ld is before "
				     "1900; the datetime strftime() "
	                             "methods require year >= 1900",
	                             year);
	                return NULL;
		}
	}

	/* Scan the input format, looking for %z/%Z/%f escapes, building
	 * a new format.  Since computing the replacements for those codes
	 * is expensive, don't unless they're actually used.
	 */
	if (format_len > INT_MAX - 1) {
		PyErr_NoMemory();
		goto Done;
	}

	totalnew = format_len + 1;	/* realistic if no %z/%Z/%f */
	newfmt = PyString_FromStringAndSize(NULL, totalnew);
	if (newfmt == NULL) goto Done;
	pnew = PyString_AsString(newfmt);
	usednew = 0;

	pin = format;
	while ((ch = *pin++) != '\0') {
		if (ch != '%') {
			ptoappend = pin - 1;
			ntoappend = 1;
		}
		else if ((ch = *pin++) == '\0') {
			/* There's a lone trailing %; doesn't make sense. */
			PyErr_SetString(PyExc_ValueError, "strftime format "
					"ends with raw %");
			goto Done;
		}
		/* A % has been seen and ch is the character after it. */
		else if (ch == 'z') {
			if (zreplacement == NULL) {
				/* format utcoffset */
				char buf[100];
				PyObject *tzinfo = get_tzinfo_member(object);
				zreplacement = PyString_FromString("");
				if (zreplacement == NULL) goto Done;
				if (tzinfo != Py_None && tzinfo != NULL) {
					assert(tzinfoarg != NULL);
					if (format_utcoffset(buf,
							     sizeof(buf),
							     "",
							     tzinfo,
							     tzinfoarg) < 0)
						goto Done;
					Py_DECREF(zreplacement);
					zreplacement = PyString_FromString(buf);
					if (zreplacement == NULL) goto Done;
				}
			}
			assert(zreplacement != NULL);
			ptoappend = PyString_AS_STRING(zreplacement);
			ntoappend = PyString_GET_SIZE(zreplacement);
		}
		else if (ch == 'Z') {
			/* format tzname */
			if (Zreplacement == NULL) {
				PyObject *tzinfo = get_tzinfo_member(object);
				Zreplacement = PyString_FromString("");
				if (Zreplacement == NULL) goto Done;
				if (tzinfo != Py_None && tzinfo != NULL) {
					PyObject *temp;
					assert(tzinfoarg != NULL);
					temp = call_tzname(tzinfo, tzinfoarg);
					if (temp == NULL) goto Done;
					if (temp != Py_None) {
						assert(PyString_Check(temp));
						/* Since the tzname is getting
						 * stuffed into the format, we
						 * have to double any % signs
						 * so that strftime doesn't
						 * treat them as format codes.
						 */
						Py_DECREF(Zreplacement);
						Zreplacement = PyObject_CallMethod(
							temp, "replace",
							"ss", "%", "%%");
						Py_DECREF(temp);
						if (Zreplacement == NULL)
							goto Done;
						if (!PyString_Check(Zreplacement)) {
							PyErr_SetString(PyExc_TypeError, "tzname.replace() did not return a string");
							goto Done;
						}
					}
					else
						Py_DECREF(temp);
				}
			}
			assert(Zreplacement != NULL);
			ptoappend = PyString_AS_STRING(Zreplacement);
			ntoappend = PyString_GET_SIZE(Zreplacement);
		}
		else if (ch == 'f') {
			/* format microseconds */
			if (freplacement == NULL) {
				freplacement = make_freplacement(object);
				if (freplacement == NULL)
					goto Done;
			}
			assert(freplacement != NULL);
			assert(PyString_Check(freplacement));
			ptoappend = PyString_AS_STRING(freplacement);
			ntoappend = PyString_GET_SIZE(freplacement);
		}
		else {
			/* percent followed by neither z nor Z */
			ptoappend = pin - 2;
			ntoappend = 2;
		}

 		/* Append the ntoappend chars starting at ptoappend to
 		 * the new format.
 		 */
 		assert(ptoappend != NULL);
 		assert(ntoappend >= 0);
 		if (ntoappend == 0)
 			continue;
 		while (usednew + ntoappend > totalnew) {
 			size_t bigger = totalnew << 1;
 			if ((bigger >> 1) != totalnew) { /* overflow */
 				PyErr_NoMemory();
 				goto Done;
 			}
 			if (_PyString_Resize(&newfmt, bigger) < 0)
 				goto Done;
 			totalnew = bigger;
 			pnew = PyString_AsString(newfmt) + usednew;
 		}
		memcpy(pnew, ptoappend, ntoappend);
		pnew += ntoappend;
		usednew += ntoappend;
		assert(usednew <= totalnew);
	}  /* end while() */

	if (_PyString_Resize(&newfmt, usednew) < 0)
		goto Done;
	{
		PyObject *time = PyImport_ImportModuleNoBlock("time");
		if (time == NULL)
			goto Done;
		result = PyObject_CallMethod(time, "strftime", "OO",
					     newfmt, timetuple);
		Py_DECREF(time);
    	}
 Done:
	Py_XDECREF(freplacement);
	Py_XDECREF(zreplacement);
	Py_XDECREF(Zreplacement);
	Py_XDECREF(newfmt);
    	return result;
}

static char *
isoformat_date(PyDateTime_Date *dt, char buffer[], int bufflen)
{
	int x;
	x = PyOS_snprintf(buffer, bufflen,
			  "%04d-%02d-%02d",
			  GET_YEAR(dt), GET_MONTH(dt), GET_DAY(dt));
	return buffer + x;
}

static void
isoformat_time(PyDateTime_DateTime *dt, char buffer[], int bufflen)
{
	int us = DATE_GET_MICROSECOND(dt);

	PyOS_snprintf(buffer, bufflen,
		      "%02d:%02d:%02d",	/* 8 characters */
		      DATE_GET_HOUR(dt),
		      DATE_GET_MINUTE(dt),
		      DATE_GET_SECOND(dt));
	if (us)
		PyOS_snprintf(buffer + 8, bufflen - 8, ".%06d", us);
}

/* ---------------------------------------------------------------------------
 * Wrap functions from the time module.  These aren't directly available
 * from C.  Perhaps they should be.
 */

/* Call time.time() and return its result (a Python float). */
static PyObject *
time_time(void)
{
	PyObject *result = NULL;
	PyObject *time = PyImport_ImportModuleNoBlock("time");

	if (time != NULL) {
		result = PyObject_CallMethod(time, "time", "()");
		Py_DECREF(time);
	}
	return result;
}

/* Build a time.struct_time.  The weekday and day number are automatically
 * computed from the y,m,d args.
 */
static PyObject *
build_struct_time(int y, int m, int d, int hh, int mm, int ss, int dstflag)
{
	PyObject *time;
	PyObject *result = NULL;

	time = PyImport_ImportModuleNoBlock("time");
	if (time != NULL) {
		result = PyObject_CallMethod(time, "struct_time",
					     "((iiiiiiiii))",
					     y, m, d,
					     hh, mm, ss,
				 	     weekday(y, m, d),
				 	     days_before_month(y, m) + d,
				 	     dstflag);
		Py_DECREF(time);
	}
	return result;
}

/* ---------------------------------------------------------------------------
 * Miscellaneous helpers.
 */

/* For obscure reasons, we need to use tp_richcompare instead of tp_compare.
 * The comparisons here all most naturally compute a cmp()-like result.
 * This little helper turns that into a bool result for rich comparisons.
 */
static PyObject *
diff_to_bool(int diff, int op)
{
	PyObject *result;
	int istrue;

	switch (op) {
		case Py_EQ: istrue = diff == 0; break;
		case Py_NE: istrue = diff != 0; break;
		case Py_LE: istrue = diff <= 0; break;
		case Py_GE: istrue = diff >= 0; break;
		case Py_LT: istrue = diff < 0; break;
		case Py_GT: istrue = diff > 0; break;
		default:
			assert(! "op unknown");
			istrue = 0; /* To shut up compiler */
	}
	result = istrue ? Py_True : Py_False;
	Py_INCREF(result);
	return result;
}

/* Raises a "can't compare" TypeError and returns NULL. */
static PyObject *
cmperror(PyObject *a, PyObject *b)
{
	PyErr_Format(PyExc_TypeError,
		     "can't compare %s to %s",
		     Py_TYPE(a)->tp_name, Py_TYPE(b)->tp_name);
	return NULL;
}

/* ---------------------------------------------------------------------------
 * Cached Python objects; these are set by the module init function.
 */

/* Conversion factors. */
static PyObject *us_per_us = NULL;	/* 1 */
static PyObject *us_per_ms = NULL;	/* 1000 */
static PyObject *us_per_second = NULL;	/* 1000000 */
static PyObject *us_per_minute = NULL;	/* 1e6 * 60 as Python int */
static PyObject *us_per_hour = NULL;	/* 1e6 * 3600 as Python long */
static PyObject *us_per_day = NULL;	/* 1e6 * 3600 * 24 as Python long */
static PyObject *us_per_week = NULL;	/* 1e6*3600*24*7 as Python long */
static PyObject *seconds_per_day = NULL; /* 3600*24 as Python int */

/* ---------------------------------------------------------------------------
 * Class implementations.
 */

/*
 * PyDateTime_Delta implementation.
 */

/* Convert a timedelta to a number of us,
 * 	(24*3600*self.days + self.seconds)*1000000 + self.microseconds
 * as a Python int or long.
 * Doing mixed-radix arithmetic by hand instead is excruciating in C,
 * due to ubiquitous overflow possibilities.
 */
static PyObject *
delta_to_microseconds(PyDateTime_Delta *self)
{
	PyObject *x1 = NULL;
	PyObject *x2 = NULL;
	PyObject *x3 = NULL;
	PyObject *result = NULL;

	x1 = PyInt_FromLong(GET_TD_DAYS(self));
	if (x1 == NULL)
		goto Done;
	x2 = PyNumber_Multiply(x1, seconds_per_day);	/* days in seconds */
	if (x2 == NULL)
		goto Done;
	Py_DECREF(x1);
	x1 = NULL;

	/* x2 has days in seconds */
	x1 = PyInt_FromLong(GET_TD_SECONDS(self));	/* seconds */
	if (x1 == NULL)
		goto Done;
	x3 = PyNumber_Add(x1, x2);	/* days and seconds in seconds */
	if (x3 == NULL)
		goto Done;
	Py_DECREF(x1);
	Py_DECREF(x2);
	x1 = x2 = NULL;

	/* x3 has days+seconds in seconds */
	x1 = PyNumber_Multiply(x3, us_per_second);	/* us */
	if (x1 == NULL)
		goto Done;
	Py_DECREF(x3);
	x3 = NULL;

	/* x1 has days+seconds in us */
	x2 = PyInt_FromLong(GET_TD_MICROSECONDS(self));
	if (x2 == NULL)
		goto Done;
	result = PyNumber_Add(x1, x2);

Done:
	Py_XDECREF(x1);
	Py_XDECREF(x2);
	Py_XDECREF(x3);
	return result;
}

/* Convert a number of us (as a Python int or long) to a timedelta.
 */
static PyObject *
microseconds_to_delta_ex(PyObject *pyus, PyTypeObject *type)
{
	int us;
	int s;
	int d;
	long temp;

	PyObject *tuple = NULL;
	PyObject *num = NULL;
	PyObject *result = NULL;

	tuple = PyNumber_Divmod(pyus, us_per_second);
	if (tuple == NULL)
		goto Done;

	num = PyTuple_GetItem(tuple, 1);	/* us */
	if (num == NULL)
		goto Done;
	temp = PyLong_AsLong(num);
	num = NULL;
	if (temp == -1 && PyErr_Occurred())
		goto Done;
	assert(0 <= temp && temp < 1000000);
	us = (int)temp;
	if (us < 0) {
		/* The divisor was positive, so this must be an error. */
		assert(PyErr_Occurred());
		goto Done;
	}

	num = PyTuple_GetItem(tuple, 0);	/* leftover seconds */
	if (num == NULL)
		goto Done;
	Py_INCREF(num);
	Py_DECREF(tuple);

	tuple = PyNumber_Divmod(num, seconds_per_day);
	if (tuple == NULL)
		goto Done;
	Py_DECREF(num);

	num = PyTuple_GetItem(tuple, 1); 	/* seconds */
	if (num == NULL)
		goto Done;
	temp = PyLong_AsLong(num);
	num = NULL;
	if (temp == -1 && PyErr_Occurred())
		goto Done;
	assert(0 <= temp && temp < 24*3600);
	s = (int)temp;

	if (s < 0) {
		/* The divisor was positive, so this must be an error. */
		assert(PyErr_Occurred());
		goto Done;
	}

	num = PyTuple_GetItem(tuple, 0);	/* leftover days */
	if (num == NULL)
		goto Done;
	Py_INCREF(num);
	temp = PyLong_AsLong(num);
	if (temp == -1 && PyErr_Occurred())
		goto Done;
	d = (int)temp;
	if ((long)d != temp) {
		PyErr_SetString(PyExc_OverflowError, "normalized days too "
				"large to fit in a C int");
		goto Done;
	}
	result = new_delta_ex(d, s, us, 0, type);

Done:
	Py_XDECREF(tuple);
	Py_XDECREF(num);
	return result;
}

#define microseconds_to_delta(pymicros)	\
	microseconds_to_delta_ex(pymicros, &PyDateTime_DeltaType)

static PyObject *
multiply_int_timedelta(PyObject *intobj, PyDateTime_Delta *delta)
{
	PyObject *pyus_in;
	PyObject *pyus_out;
	PyObject *result;

	pyus_in = delta_to_microseconds(delta);
	if (pyus_in == NULL)
		return NULL;

	pyus_out = PyNumber_Multiply(pyus_in, intobj);
	Py_DECREF(pyus_in);
	if (pyus_out == NULL)
		return NULL;

	result = microseconds_to_delta(pyus_out);
	Py_DECREF(pyus_out);
	return result;
}

static PyObject *
divide_timedelta_int(PyDateTime_Delta *delta, PyObject *intobj)
{
	PyObject *pyus_in;
	PyObject *pyus_out;
	PyObject *result;

	pyus_in = delta_to_microseconds(delta);
	if (pyus_in == NULL)
		return NULL;

	pyus_out = PyNumber_FloorDivide(pyus_in, intobj);
	Py_DECREF(pyus_in);
	if (pyus_out == NULL)
		return NULL;

	result = microseconds_to_delta(pyus_out);
	Py_DECREF(pyus_out);
	return result;
}

static PyObject *
delta_add(PyObject *left, PyObject *right)
{
	PyObject *result = Py_NotImplemented;

	if (PyDelta_Check(left) && PyDelta_Check(right)) {
		/* delta + delta */
		/* The C-level additions can't overflow because of the
		 * invariant bounds.
		 */
		int days = GET_TD_DAYS(left) + GET_TD_DAYS(right);
		int seconds = GET_TD_SECONDS(left) + GET_TD_SECONDS(right);
		int microseconds = GET_TD_MICROSECONDS(left) +
				   GET_TD_MICROSECONDS(right);
		result = new_delta(days, seconds, microseconds, 1);
	}

	if (result == Py_NotImplemented)
		Py_INCREF(result);
	return result;
}

static PyObject *
delta_negative(PyDateTime_Delta *self)
{
	return new_delta(-GET_TD_DAYS(self),
			 -GET_TD_SECONDS(self),
			 -GET_TD_MICROSECONDS(self),
			 1);
}

static PyObject *
delta_positive(PyDateTime_Delta *self)
{
	/* Could optimize this (by returning self) if this isn't a
	 * subclass -- but who uses unary + ?  Approximately nobody.
	 */
	return new_delta(GET_TD_DAYS(self),
			 GET_TD_SECONDS(self),
			 GET_TD_MICROSECONDS(self),
			 0);
}

static PyObject *
delta_abs(PyDateTime_Delta *self)
{
	PyObject *result;

	assert(GET_TD_MICROSECONDS(self) >= 0);
	assert(GET_TD_SECONDS(self) >= 0);

	if (GET_TD_DAYS(self) < 0)
		result = delta_negative(self);
	else
		result = delta_positive(self);

	return result;
}

static PyObject *
delta_subtract(PyObject *left, PyObject *right)
{
	PyObject *result = Py_NotImplemented;

	if (PyDelta_Check(left) && PyDelta_Check(right)) {
	    	/* delta - delta */
	    	PyObject *minus_right = PyNumber_Negative(right);
	    	if (minus_right) {
	    		result = delta_add(left, minus_right);
	    		Py_DECREF(minus_right);
	    	}
	    	else
	    		result = NULL;
	}

	if (result == Py_NotImplemented)
		Py_INCREF(result);
	return result;
}

/* This is more natural as a tp_compare, but doesn't work then:  for whatever
 * reason, Python's try_3way_compare ignores tp_compare unless
 * PyInstance_Check returns true, but these aren't old-style classes.
 */
static PyObject *
delta_richcompare(PyDateTime_Delta *self, PyObject *other, int op)
{
	int diff = 42;	/* nonsense */

	if (PyDelta_Check(other)) {
		diff = GET_TD_DAYS(self) - GET_TD_DAYS(other);
		if (diff == 0)…