Split qtLocalTime out into a new QLocalTime namespace

... in new qlocaltime* files, now that it's decoupled enough from the
internals of QDateTime for this to be possible. Part of the
consolidation of time_t code in one place.

Move assorted constants from qdatetime.cpp to a private namespace in
qdatetimeprivate_p.h to be shared between q*time.cpp hereafter (fixing
an out of date comment in the process - julianDayFromDate() is long
gone).

Task-number: QTBUG-95993
Change-Id: I03d97e959118041f9d86b8bb2e738599bc0b17e1
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

6 files changed, 161 insertions, 77 deletions

diff --git a/src/corelib/CMakeLists.txt b/src/corelib/CMakeLists.txt
index 2615a71f8b..5fd60b5ac9 100644
--- a/src/corelib/CMakeLists.txt
+++ b/src/corelib/CMakeLists.txt
@@ -216,6 +216,7 @@ qt_internal_add_module(Core
         time/qcalendarbackend_p.h
         time/qcalendarmath_p.h
         time/qdatetime.cpp time/qdatetime.h time/qdatetime_p.h
+        time/qlocaltime.cpp time/qlocaltime_p.h
         time/qgregoriancalendar.cpp time/qgregoriancalendar_p.h
         time/qjuliancalendar.cpp time/qjuliancalendar_p.h
         time/qmilankoviccalendar.cpp time/qmilankoviccalendar_p.h
diff --git a/src/corelib/time/qdatetime.cpp b/src/corelib/time/qdatetime.cpp
index 817f37d4a4..27d31cca8f 100644
--- a/src/corelib/time/qdatetime.cpp
+++ b/src/corelib/time/qdatetime.cpp
@@ -20,6 +20,7 @@
 #include "private/qcore_mac_p.h"
 #endif
 #include "private/qgregoriancalendar_p.h"
+#include "private/qlocaltime_p.h"
 #include "private/qnumeric_p.h"
 #include "private/qstringiterator_p.h"
 #if QT_CONFIG(timezone)
@@ -35,20 +36,13 @@
 QT_BEGIN_NAMESPACE
 
 using namespace Qt::StringLiterals;
+using namespace QtPrivate::DateTimeConstants;
 
 /*****************************************************************************
   Date/Time Constants
  *****************************************************************************/
 
-constexpr qint64 SECS_PER_DAY = 86400;
-constexpr qint64 MSECS_PER_DAY = 86400000;
-constexpr qint64 SECS_PER_HOUR = 3600;
-constexpr qint64 MSECS_PER_HOUR = 3600000;
-constexpr qint64 SECS_PER_MIN = 60;
-constexpr qint64 MSECS_PER_MIN = 60000;
-constexpr qint64 MSECS_PER_SEC = 1000;
 constexpr qint64 TIME_T_MAX = std::numeric_limits<time_t>::max();
-constexpr qint64 JULIAN_DAY_FOR_EPOCH = 2440588; // result of julianDayFromDate(1970, 1, 1)
 
 /*****************************************************************************
   QDate static helper functions
@@ -2564,73 +2558,6 @@ static inline bool callMkTime(tm *local, time_t *secs)
     return good;
 }
 
-namespace {
-bool qtLocalTime(time_t utc, struct tm *local)
-{
-    // localtime() is specified to work as if it called tzset().
-    // localtime_r() does not have this constraint, so make an explicit call.
-    // The explicit call should also request a re-parse of timezone info.
-    qTzSet();
-#if defined(Q_OS_WIN)
-    return !localtime_s(local, &utc);
-#elif QT_CONFIG(thread) && defined(_POSIX_THREAD_SAFE_FUNCTIONS)
-    // Use the reentrant version of localtime() where available
-    // as is thread-safe and doesn't use a shared static data area
-    if (tm *res = localtime_r(&utc, local)) {
-        Q_ASSERT(res == local);
-        return true;
-    }
-    return false;
-#else
-    // Returns shared static data which may be overwritten at any time
-    // So copy the result asap
-    if (tm *res = localtime(&utc)) {
-        *local = *res;
-        return true;
-    }
-    return false;
-#endif
-}
-
-// Calls the platform variant of localtime() for the given utcMillis, and
-// returns the local milliseconds, offset from UTC and DST status.
-QDateTimePrivate::ZoneState utcToLocal(qint64 utcMillis)
-{
-    const int signFix = utcMillis % MSECS_PER_SEC && utcMillis < 0 ? 1 : 0;
-    const time_t epochSeconds = utcMillis / MSECS_PER_SEC - signFix;
-    const int msec = utcMillis % MSECS_PER_SEC + signFix * MSECS_PER_SEC;
-    Q_ASSERT(msec >= 0 && msec < MSECS_PER_SEC);
-    if (qint64(epochSeconds) * MSECS_PER_SEC + msec != utcMillis)
-        return {utcMillis};
-
-    tm local;
-    if (!qtLocalTime(epochSeconds, &local))
-        return {utcMillis};
-
-    qint64 jd;
-    if (Q_UNLIKELY(!QGregorianCalendar::julianFromParts(qYearFromTmYear(local.tm_year),
-                                                        local.tm_mon + 1, local.tm_mday, &jd))) {
-        return {utcMillis};
-    }
-    const qint64 daySeconds
-        = local.tm_hour * SECS_PER_HOUR + local.tm_min * SECS_PER_MIN + local.tm_sec;
-    Q_ASSERT(0 <= daySeconds && daySeconds < SECS_PER_DAY);
-    qint64 localSeconds, localMillis;
-    if (Q_UNLIKELY(
-            mul_overflow(jd - JULIAN_DAY_FOR_EPOCH, std::integral_constant<qint64, SECS_PER_DAY>(),
-                         &localSeconds)
-            || add_overflow(localSeconds, daySeconds, &localSeconds)
-            || mul_overflow(localSeconds, std::integral_constant<qint64, MSECS_PER_SEC>(),
-                            &localMillis)
-            || add_overflow(localMillis, qint64(msec), &localMillis))) {
-        return {utcMillis};
-    }
-    const auto dst
-        = local.tm_isdst ? QDateTimePrivate::DaylightTime : QDateTimePrivate::StandardTime;
-    return { localMillis, int(localSeconds - epochSeconds), dst };
-}
-}
-
 // Converts milliseconds since the start of 1970 into a date and/or time:
 static qint64 msecsToJulianDay(qint64 msecs)
 {
@@ -2903,7 +2830,7 @@ QDateTimePrivate::ZoneState QDateTimePrivate::expressUtcAsLocal(qint64 utcMSecs)
     ZoneState result{utcMSecs};
     // Within the time_t supported range, localtime() can handle it:
     if (millisInSystemRange(utcMSecs)) {
-        result = utcToLocal(utcMSecs);
+        result = QLocalTime::utcToLocal(utcMSecs);
         if (result.valid)
             return result;
     }
@@ -2935,7 +2862,7 @@ QDateTimePrivate::ZoneState QDateTimePrivate::expressUtcAsLocal(qint64 utcMSecs)
         return result;
     }
 
-    result = utcToLocal(fakeUtc);
+    result = QLocalTime::utcToLocal(fakeUtc);
     // Now correct result.when for the use of the fake date:
     if (!result.valid || add_overflow(result.when, diffMillis, &result.when)) {
         // If utcToLocal() failed, its return has the fake when; restore utcMSecs.
diff --git a/src/corelib/time/qdatetime_p.h b/src/corelib/time/qdatetime_p.h
index cccaba840a..0636a3a223 100644
--- a/src/corelib/time/qdatetime_p.h
+++ b/src/corelib/time/qdatetime_p.h
@@ -111,6 +111,22 @@ public:
 
 Q_DECLARE_OPERATORS_FOR_FLAGS(QDateTimePrivate::StatusFlags)
 
+namespace QtPrivate {
+namespace DateTimeConstants {
+
+constexpr qint64 SECS_PER_MIN = 60;
+constexpr qint64 SECS_PER_HOUR = SECS_PER_MIN * 60;
+constexpr qint64 SECS_PER_DAY = SECS_PER_HOUR * 24;
+
+constexpr qint64 MSECS_PER_SEC = 1000;
+constexpr qint64 MSECS_PER_MIN = SECS_PER_MIN * MSECS_PER_SEC;
+constexpr qint64 MSECS_PER_HOUR = SECS_PER_HOUR * MSECS_PER_SEC;
+constexpr qint64 MSECS_PER_DAY = SECS_PER_DAY * MSECS_PER_SEC;
+
+constexpr qint64 JULIAN_DAY_FOR_EPOCH = 2440588; // result of QDate(1970, 1, 1).toJulianDay()
+}
+}
+
 QT_END_NAMESPACE
 
 #endif // QDATETIME_P_H
diff --git a/src/corelib/time/qlocaltime.cpp b/src/corelib/time/qlocaltime.cpp
new file mode 100644
index 0000000000..589a6e7688
--- /dev/null
+++ b/src/corelib/time/qlocaltime.cpp
@@ -0,0 +1,108 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#include "qlocaltime_p.h"
+#include "qplatformdefs.h"
+
+#include "private/qgregoriancalendar_p.h"
+#include "private/qnumeric_p.h"
+#if QT_CONFIG(timezone)
+#include "private/qtimezoneprivate_p.h"
+#endif
+
+#include <time.h>
+#ifdef Q_OS_WIN
+#  include <qt_windows.h>
+#endif
+
+QT_BEGIN_NAMESPACE
+
+using namespace QtPrivate::DateTimeConstants;
+namespace {
+/*
+    Qt represents n BCE as -n, whereas struct tm's tm_year field represents a
+    year by the number of years after (negative for before) 1900, so that 1+m
+    BCE is -1900 -m; so treating 1 BCE as 0 CE. We thus shift by different
+    offsets depending on whether the year is BCE or CE.
+*/
+// constexpr int tmYearFromQYear(int year) { return year - (year < 0 ? 1899 : 1900); }
+constexpr int qYearFromTmYear(int year) { return year + (year < -1899 ? 1899 : 1900); }
+
+bool qtLocalTime(time_t utc, struct tm *local)
+{
+    // This should really be done under the environmentMutex wrapper qglobal.cpp
+    // uses in qTzSet() and friends. However, the only sane way to do that would
+    // be to move this whole function there (and replace its qTzSet() with a
+    // naked tzset(), since it'd already be mutex-protected).
+#if defined(Q_OS_WIN)
+    // The doc of localtime_s() doesn't explicitly say that it calls _tzset(),
+    // but does say that localtime_s() corrects for the same things _tzset()
+    // sets the globals for, so presumably localtime_s() behaves as if it did.
+    return !localtime_s(local, &utc);
+#elif QT_CONFIG(thread) && defined(_POSIX_THREAD_SAFE_FUNCTIONS)
+    // Use the reentrant version of localtime() where available, as it is
+    // thread-safe and doesn't use a shared static data area.
+    // As localtime() is specified to work as if it called tzset(), but
+    // localtime_r() does not have this constraint, make an explicit call.
+    // The explicit call should also request a re-parse of timezone info.
+    qTzSet();
+    if (tm *res = localtime_r(&utc, local)) {
+        Q_ASSERT(res == local);
+        return true;
+    }
+    return false;
+#else
+    // Returns shared static data which may be overwritten at any time
+    // So copy the result asap
+    if (tm *res = localtime(&utc)) {
+        *local = *res;
+        return true;
+    }
+    return false;
+#endif
+}
+} // namespace
+
+namespace QLocalTime {
+
+// Calls the platform variant of localtime() for the given utcMillis, and
+// returns the local milliseconds, offset from UTC and DST status.
+QDateTimePrivate::ZoneState utcToLocal(qint64 utcMillis)
+{
+    const int signFix = utcMillis % MSECS_PER_SEC && utcMillis < 0 ? 1 : 0;
+    const time_t epochSeconds = utcMillis / MSECS_PER_SEC - signFix;
+    const int msec = utcMillis % MSECS_PER_SEC + signFix * MSECS_PER_SEC;
+    Q_ASSERT(msec >= 0 && msec < MSECS_PER_SEC);
+    if (qint64(epochSeconds) * MSECS_PER_SEC + msec != utcMillis)
+        return {utcMillis};
+
+    tm local;
+    if (!qtLocalTime(epochSeconds, &local))
+        return {utcMillis};
+
+    qint64 jd;
+    if (Q_UNLIKELY(!QGregorianCalendar::julianFromParts(qYearFromTmYear(local.tm_year),
+                                                        local.tm_mon + 1, local.tm_mday, &jd))) {
+        return {utcMillis};
+    }
+    const qint64 daySeconds
+        = (local.tm_hour * 60 + local.tm_min) * 60 + local.tm_sec;
+    Q_ASSERT(0 <= daySeconds && daySeconds < SECS_PER_DAY);
+    qint64 localSeconds, localMillis;
+    if (Q_UNLIKELY(
+            mul_overflow(jd - JULIAN_DAY_FOR_EPOCH, std::integral_constant<qint64, SECS_PER_DAY>(),
+                         &localSeconds)
+            || add_overflow(localSeconds, daySeconds, &localSeconds)
+            || mul_overflow(localSeconds, std::integral_constant<qint64, MSECS_PER_SEC>(),
+                            &localMillis)
+            || add_overflow(localMillis, qint64(msec), &localMillis))) {
+        return {utcMillis};
+    }
+    const auto dst
+        = local.tm_isdst ? QDateTimePrivate::DaylightTime : QDateTimePrivate::StandardTime;
+    return { localMillis, int(localSeconds - epochSeconds), dst };
+}
+
+} // QLocalTime
+
+QT_END_NAMESPACE
diff --git a/src/corelib/time/qlocaltime_p.h b/src/corelib/time/qlocaltime_p.h
new file mode 100644
index 0000000000..2a7b7bc098
--- /dev/null
+++ b/src/corelib/time/qlocaltime_p.h
@@ -0,0 +1,31 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#ifndef QLOCALTIME_P_H
+#define QLOCALTIME_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an implementation
+// detail.  This header file may change from version to version without notice,
+// or even be removed.
+//
+// We mean it.
+//
+
+#include <QtCore/private/qglobal_p.h>
+#include <QtCore/private/qdatetime_p.h>
+
+QT_BEGIN_NAMESPACE
+
+// Packaging system time_t functions
+namespace QLocalTime {
+// Support for QDateTime
+QDateTimePrivate::ZoneState utcToLocal(qint64 utcMillis);
+}
+
+QT_END_NAMESPACE
+
+#endif // QLOCALTIME_P_H
diff --git a/src/tools/bootstrap/CMakeLists.txt b/src/tools/bootstrap/CMakeLists.txt
index 2f69849538..0d920624af 100644
--- a/src/tools/bootstrap/CMakeLists.txt
+++ b/src/tools/bootstrap/CMakeLists.txt
@@ -71,6 +71,7 @@ qt_internal_extend_target(Bootstrap
         ../../corelib/time/qcalendar.cpp
         ../../corelib/time/qdatetime.cpp
         ../../corelib/time/qgregoriancalendar.cpp
+        ../../corelib/time/qlocaltime.cpp
         ../../corelib/time/qromancalendar.cpp
         ../../corelib/tools/qarraydata.cpp
         ../../corelib/tools/qbitarray.cpp