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Replace ruleForYear() method with a local index-based function

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Removed private method of QWinTimeZonePrivate in favor of a local
static that returns a rule index rather than a rule; this prepares the
way for smarter searching in transition-finding methods.  In the
process, re-work the function to use binary chop instead of a linear
search through a potentially long sorted list.

Change-Id: I2171e3f01afa3037b9718e1be7d0c9343aa74ff0
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Edward Welbourne 2017-10-26 17:04:05 +02:00
parent 10745de279
commit f0fc28ee30
2 changed files with 35 additions and 16 deletions
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1
src/corelib/tools/qtimezoneprivate_p.h
View File

@ -431,7 +431,6 @@ public:
private:
void init(const QByteArray &ianaId);
QWinTransitionRule ruleForYear(int year) const;
QTimeZonePrivate::Data ruleToData(const QWinTransitionRule &rule, qint64 atMSecsSinceEpoch,
QTimeZone::TimeType type) const;

50
src/corelib/tools/qtimezoneprivate_win.cpp
View File

@ -393,6 +393,34 @@ static QLocale::Country userCountry()
: QLocale::AnyCountry;
}
// Index of last rule in rules with .startYear <= year:
static int ruleIndexForYear(const QList<QWinTimeZonePrivate::QWinTransitionRule> &rules, int year)
{
if (rules.last().startYear <= year)
return rules.count() - 1;
// We don't have a rule for before the first, but the first is the best we can offer:
if (rules.first().startYear > year)
return 0;
// Otherwise, use binary chop:
int lo = 0, hi = rules.count();
// invariant: rules[i].startYear <= year < rules[hi].startYear
// subject to treating rules[rules.count()] as "off the end of time"
while (lo + 1 < hi) {
const int mid = (lo + hi) / 2;
// lo + 2 <= hi, so lo + 1 <= mid <= hi - 1, so lo < mid < hi
// In particular, mid < rules.count()
const int midYear = rules.at(mid).startYear;
if (midYear > year)
hi = mid;
else if (midYear < year)
lo = mid;
else // No two rules have the same startYear:
return mid;
}
return lo;
}
// Create the system default time zone
QWinTimeZonePrivate::QWinTimeZonePrivate()
: QTimeZonePrivate()
@ -522,7 +550,8 @@ QString QWinTimeZonePrivate::displayName(QTimeZone::TimeType timeType,
Q_UNUSED(locale);
if (nameType == QTimeZone::OffsetName) {
QWinTransitionRule rule = ruleForYear(QDate::currentDate().year());
const QWinTransitionRule &rule =
m_tranRules.at(ruleIndexForYear(m_tranRules, QDate::currentDate().year()));
if (timeType == QTimeZone::DaylightTime)
return isoOffsetFormat((rule.standardTimeBias + rule.daylightTimeBias) * -60);
else
@ -582,7 +611,7 @@ QTimeZonePrivate::Data QWinTimeZonePrivate::data(qint64 forMSecsSinceEpoch) cons
QWinTransitionRule rule;
do {
// Convert the transition rules into msecs for the year we want to try
rule = ruleForYear(year);
rule = m_tranRules.at(ruleIndexForYear(m_tranRules, year));
// If no transition rules to calculate then no DST, so just use rule for std
if (rule.standardTimeRule.wMonth == 0 && rule.daylightTimeRule.wMonth == 0)
break;
@ -624,7 +653,7 @@ QTimeZonePrivate::Data QWinTimeZonePrivate::nextTransition(qint64 afterMSecsSinc
// If the required year falls after the last rule start year and the last rule has no
// valid future transition calculations then there is no next transition
if (year > m_tranRules.last().startYear) {
rule = ruleForYear(year);
rule = m_tranRules.at(ruleIndexForYear(m_tranRules, year));
// If the rules have either a fixed year, or no month, then no future trans
if (rule.standardTimeRule.wYear != 0 || rule.daylightTimeRule.wYear != 0
|| rule.standardTimeRule.wMonth == 0 || rule.daylightTimeRule.wMonth == 0) {
@ -640,7 +669,7 @@ QTimeZonePrivate::Data QWinTimeZonePrivate::nextTransition(qint64 afterMSecsSinc
TransitionTimePair pair;
do {
// Convert the transition rules into msecs for the year we want to try
rule = ruleForYear(year);
rule = m_tranRules.at(ruleIndexForYear(m_tranRules, year));
// If no transition rules to calculate then no next transition
if (rule.standardTimeRule.wMonth == 0 && rule.daylightTimeRule.wMonth == 0)
return invalidData();
@ -676,7 +705,7 @@ QTimeZonePrivate::Data QWinTimeZonePrivate::previousTransition(qint64 beforeMSec
// If the required year falls before the first rule start year and the first rule has no
// valid transition calculations then there is no previous transition
if (year < m_tranRules.first().startYear) {
rule = ruleForYear(year);
rule = m_tranRules.at(ruleIndexForYear(m_tranRules, year));
// If the rules have either a fixed year, or no month, then no previous trans
if (rule.standardTimeRule.wYear != 0 || rule.daylightTimeRule.wYear != 0
|| rule.standardTimeRule.wMonth == 0 || rule.daylightTimeRule.wMonth == 0) {
@ -690,7 +719,7 @@ QTimeZonePrivate::Data QWinTimeZonePrivate::previousTransition(qint64 beforeMSec
TransitionTimePair pair;
do {
// Convert the transition rules into msecs for the year we want to try
rule = ruleForYear(year);
rule = m_tranRules.at(ruleIndexForYear(m_tranRules, year));
// If no transition rules to calculate then no previous transition
if (rule.standardTimeRule.wMonth == 0 && rule.daylightTimeRule.wMonth == 0)
return invalidData();
@ -745,15 +774,6 @@ QList<QByteArray> QWinTimeZonePrivate::availableTimeZoneIds() const
return result;
}
QWinTimeZonePrivate::QWinTransitionRule QWinTimeZonePrivate::ruleForYear(int year) const
{
for (int i = m_tranRules.size() - 1; i >= 0; --i) {
if (m_tranRules.at(i).startYear <= year)
return m_tranRules.at(i);
}
return m_tranRules.at(0);
}
QTimeZonePrivate::Data QWinTimeZonePrivate::ruleToData(const QWinTransitionRule &rule,
qint64 atMSecsSinceEpoch,
QTimeZone::TimeType type) const