datetimetz_astimezone(): Speed optimizations -- although I'd rather

find a more elegant algorithm (OTOH, the hairy new implementation allows
user-written tzinfo classes to be elegant, so it's a big win even if
astimezone() remains hairy).

Darn!  I've only got 10 minutes left to get falling-down drunk!  I suppose
I'll have to smoke crack instead now.

diff --git a/Modules/datetimemodule.c b/Modules/datetimemodule.c
index 40f4773447af754acbee26721639cdfc309d68d6..fb1f9e1ee9dfb5e85692bb9d56a8ddda13f0c9ea 100644 (file)
--- a/Modules/datetimemodule.c
+++ b/Modules/datetimemodule.c
@@ -4753,7 +4753,7 @@ datetimetz_astimezone(PyDateTime_DateTimeTZ *self, PyObject *args,
 
        PyObject *result;
        PyObject *temp;
-       int myoff, otoff, newoff;
+       int selfoff, resoff, tempoff, total_added_to_result;
        int none;
 
        PyObject *tzinfo;
@@ -4776,21 +4776,23 @@ datetimetz_astimezone(PyDateTime_DateTimeTZ *self, PyObject *args,
         /* Get the offsets.  If either object turns out to be naive, again
          * there's no conversion of date or time fields.
          */
-       myoff = call_utcoffset(self->tzinfo, (PyObject *)self, &none);
-       if (myoff == -1 && PyErr_Occurred())
+       selfoff = call_utcoffset(self->tzinfo, (PyObject *)self, &none);
+       if (selfoff == -1 && PyErr_Occurred())
                goto Fail;
        if (none)
                return result;
 
-       otoff = call_utcoffset(tzinfo, result, &none);
-       if (otoff == -1 && PyErr_Occurred())
+       resoff = call_utcoffset(tzinfo, result, &none);
+       if (resoff == -1 && PyErr_Occurred())
                goto Fail;
        if (none)
                return result;
 
-       /* Add otoff-myoff to result. */
-       mm += otoff - myoff;
-       if (normalize_datetime(&y, &m, &d, &hh, &mm, &ss, &us) < 0)
+       /* Add resoff-selfoff to result. */
+       total_added_to_result = resoff - selfoff;
+       mm += total_added_to_result;
+       if ((mm < 0 || mm >= 60) &&
+           normalize_datetime(&y, &m, &d, &hh, &mm, &ss, &us) < 0)
                goto Fail;
        temp = new_datetimetz(y, m, d, hh, mm, ss, us, tzinfo);
        if (temp == NULL)
@@ -4805,16 +4807,19 @@ datetimetz_astimezone(PyDateTime_DateTimeTZ *self, PyObject *args,
         * Unfortunately, we can be in trouble even if we didn't cross a
         * DST boundary, if we landed on one of the DST "problem hours".
         */
-       newoff = call_utcoffset(tzinfo, result, &none);
-       if (newoff == -1 && PyErr_Occurred())
+       tempoff = call_utcoffset(tzinfo, result, &none);
+       if (tempoff == -1 && PyErr_Occurred())
                goto Fail;
        if (none)
                goto Inconsistent;
 
-       if (newoff != otoff) {
+       if (tempoff != resoff) {
                /* We did cross a boundary.  Try to correct. */
-               mm += newoff - otoff;
-               if (normalize_datetime(&y, &m, &d, &hh, &mm, &ss, &us) < 0)
+               const int delta = tempoff - resoff;
+               total_added_to_result += delta;
+               mm += delta;
+               if ((mm < 0 || mm >= 60) &&
+                   normalize_datetime(&y, &m, &d, &hh, &mm, &ss, &us) < 0)
                        goto Fail;
                temp = new_datetimetz(y, m, d, hh, mm, ss, us, tzinfo);
                if (temp == NULL)
@@ -4822,8 +4827,8 @@ datetimetz_astimezone(PyDateTime_DateTimeTZ *self, PyObject *args,
                Py_DECREF(result);
                result = temp;
 
-               otoff = call_utcoffset(tzinfo, result, &none);
-               if (otoff == -1 && PyErr_Occurred())
+               resoff = call_utcoffset(tzinfo, result, &none);
+               if (resoff == -1 && PyErr_Occurred())
                        goto Fail;
                if (none)
                        goto Inconsistent;
@@ -4834,13 +4839,13 @@ datetimetz_astimezone(PyDateTime_DateTimeTZ *self, PyObject *args,
         * sense on the local clock.  So force that.
         */
        hh -= 1;
-       if (normalize_datetime(&y, &m, &d, &hh, &mm, &ss, &us) < 0)
+       if (hh < 0 && normalize_datetime(&y, &m, &d, &hh, &mm, &ss, &us) < 0)
                goto Fail;
        temp = new_datetimetz(y, m, d, hh, mm, ss, us, tzinfo);
        if (temp == NULL)
                goto Fail;
-       newoff = call_utcoffset(tzinfo, temp, &none);
-       if (newoff == -1 && PyErr_Occurred()) {
+       tempoff = call_utcoffset(tzinfo, temp, &none);
+       if (tempoff == -1 && PyErr_Occurred()) {
                Py_DECREF(temp);
                goto Fail;
        }
@@ -4849,11 +4854,11 @@ datetimetz_astimezone(PyDateTime_DateTimeTZ *self, PyObject *args,
                goto Inconsistent;
        }
        /* Are temp and result really the same time?  temp == result iff
-        * temp - newoff == result - otoff, iff
-        * (result - HOUR) - newoff = result - otoff, iff
-        * otoff - newoff == HOUR
+        * temp - tempoff == result - resoff, iff
+        * (result - HOUR) - tempoff = result - resoff, iff
+        * resoff - tempoff == HOUR
         */
-       if (otoff - newoff == 60) {
+       if (resoff - tempoff == 60) {
                /* use the local time that makes sense */
                Py_DECREF(result);
                return temp;
@@ -4861,18 +4866,19 @@ datetimetz_astimezone(PyDateTime_DateTimeTZ *self, PyObject *args,
        Py_DECREF(temp);
 
        /* There's still a problem with the unspellable (in local time)
-        * hour after DST ends.
+        * hour after DST ends.  If self and result map to the same UTC time
+        * time, we're OK, else the hour is unrepresentable in the tzinfo
+        * zone.  The result's local time now is
+        * self + total_added_to_result, so self == result iff
+        * self - selfoff == result - resoff, iff
+        * self - selfoff == (self + total_added_to_result) - resoff, iff
+        * - selfoff == total_added_to_result - resoff, iff
+        * total_added_to_result == resoff - selfoff
         */
-       temp = datetime_richcompare((PyDateTime_DateTime *)self,
-                                   result, Py_EQ);
-       if (temp == NULL)
-               goto Fail;
-       if (temp == Py_True) {
-               Py_DECREF(temp);
+       if (total_added_to_result == resoff - selfoff)
                return result;
-       }
-       Py_DECREF(temp);
-        /* Else there's no way to spell self in zone other.tz. */
+
+        /* Else there's no way to spell self in zone tzinfo. */
         PyErr_SetString(PyExc_ValueError, "astimezone(): the source "
                        "datetimetz can't be expressed in the target "
                        "timezone's local time");