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ICU-23004 bidirectional reverse_iterator

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Markus Scherer 2025-03-06 16:25:23 -08:00
parent 4da330d2e2
commit be7197dd36
1 changed files with 91 additions and 57 deletions
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148
icu4c/source/common/unicode/utfiter.h
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@ -1062,7 +1062,7 @@ public:
inline bool operator==(const UTFIterator &other) const {
return p_ == other.p_ && ahead_ == other.ahead_;
// Strictly speaking, we should check if the logical position is the same.
// However, we cannot move, or do arithmetic with, a single-pass UnitIter.
// However, we cannot advance, or do arithmetic with, a single-pass UnitIter.
}
inline bool operator!=(const UTFIterator &other) const { return !operator==(other); }
@ -1149,9 +1149,8 @@ public:
using iterator_category = std::bidirectional_iterator_tag;
inline reverse_iterator(U_HEADER_ONLY_NAMESPACE::UTFIterator<UnitIter, CP32, behavior> iter) :
p_(iter.getLogicalPosition()),
start_(iter.start_), units_(0, 0, false, p_), unitsLimit_(p_) {}
// TODO: limit_
p_(iter.getLogicalPosition()), start_(iter.start_), limit_(iter.limit_),
units_(0, 0, false, p_), unitsLimit_(p_) {}
inline reverse_iterator(const reverse_iterator &other) = default;
inline reverse_iterator &operator=(const reverse_iterator &other) = default;
@ -1162,58 +1161,66 @@ public:
inline bool operator!=(const reverse_iterator &other) const { return !operator==(other); }
inline CodeUnits_ operator*() const {
if (!behind_) {
if (state_ == 0) {
unitsLimit_ = p_;
units_ = Impl::decAndRead(start_, p_);
behind_ = true;
state_ = -1;
}
return units_;
}
inline Proxy operator->() const {
if (!behind_) {
if (state_ == 0) {
unitsLimit_ = p_;
units_ = Impl::decAndRead(start_, p_);
behind_ = true;
state_ = -1;
}
return Proxy(units_);
}
inline reverse_iterator &operator++() { // pre-increment
if (behind_) {
if (state_ < 0) {
// operator*() called decAndRead() so p_ is already behind.
behind_ = false;
} else {
state_ = 0;
} else if (state_ == 0) {
Impl::dec(start_, p_);
} else /* state_ > 0 */ {
// operator--() called readAndInc() so we know how far to skip.
p_ = units_.data();
state_ = 0;
}
return *this;
}
inline reverse_iterator operator++(int) { // post-increment
if (behind_) {
if (state_ < 0) {
// operator*() called decAndRead() so p_ is already behind.
reverse_iterator result(*this);
behind_ = false;
state_ = 0;
return result;
} else {
} else if (state_ == 0) {
unitsLimit_ = p_;
units_ = Impl::decAndRead(start_, p_);
reverse_iterator result(*this);
result.behind_ = true;
// keep this->behind_ == false
result.state_ = -1;
// keep this->state_ == 0
return result;
} else /* state_ > 0 */ {
reverse_iterator result(*this);
// operator--() called readAndInc() so we know how far to skip.
p_ = units_.data();
state_ = 0;
return result;
}
}
inline reverse_iterator &operator--() { // pre-decrement
#if 0 // TODO
if (state_ > 0) {
// operator*() called readAndInc() so p_ is ahead of the logical position.
p_ = units_.data();
if (state_ < 0) {
// operator*() called decAndRead() so p_ is behind the logical position.
p_ = unitsLimit_;
}
units_ = Impl::decAndRead(start_, p_);
state_ = -1;
#endif
units_ = Impl::readAndInc(start_, p_);
state_ = 1;
return *this;
}
@ -1225,22 +1232,25 @@ public:
private:
inline UnitIter getLogicalPosition() const {
return !behind_ ? p_ : unitsLimit_;
return state_ >= 0 ? p_ : unitsLimit_;
}
// operator*() etc. are logically const.
mutable UnitIter p_;
// In a validating iterator, we need start_ so that when we read a code point
// backward we can test if there are enough code units.
// In a validating iterator, we need start_ & limit_ so that when we read a code point
// (forward or backward) we can test if there are enough code units.
const UnitIter start_;
const UnitIter limit_;
// Keep state so that we call decAndRead() only once for both operator*() and ++
// to make it easy for the compiler to optimize.
mutable CodeUnits_ units_;
// For fast getLogicalPosition() and operator==().
mutable UnitIter unitsLimit_;
// true: units_ = decAndRead(), p_ = units start
// >0: units_ = readAndInc(), p_ = units limit
// 0: initial state
// <0: units_ = decAndRead(), p_ = units start
// which means that p_ is behind its logical position
// false: initial state
mutable bool behind_ = false;
mutable int8_t state_ = 0;
};
#endif // U_IN_DOXYGEN
@ -1283,12 +1293,18 @@ public:
return {s.data(), limit, limit};
}
/** @draft ICU 78 */
/**
* @return reverse_iterator(end())
* @draft ICU 78
*/
auto rbegin() const {
return std::make_reverse_iterator(end());
}
/** @draft ICU 78 */
/**
* @return reverse_iterator(begin())
* @draft ICU 78
*/
auto rend() const {
return std::make_reverse_iterator(begin());
}
@ -1487,7 +1503,7 @@ public:
inline bool operator==(const UnsafeUTFIterator &other) const {
return p_ == other.p_ && ahead_ == other.ahead_;
// Strictly speaking, we should check if the logical position is the same.
// However, we cannot move, or do arithmetic with, a single-pass UnitIter.
// However, we cannot advance, or do arithmetic with, a single-pass UnitIter.
}
inline bool operator!=(const UnsafeUTFIterator &other) const { return !operator==(other); }
@ -1582,58 +1598,66 @@ public:
inline bool operator!=(const reverse_iterator &other) const { return !operator==(other); }
inline UnsafeCodeUnits_ operator*() const {
if (!behind_) {
if (state_ == 0) {
unitsLimit_ = p_;
units_ = Impl::decAndRead(p_);
behind_ = true;
state_ = -1;
}
return units_;
}
inline Proxy operator->() const {
if (!behind_) {
if (state_ == 0) {
unitsLimit_ = p_;
units_ = Impl::decAndRead(p_);
behind_ = true;
state_ = -1;
}
return Proxy(units_);
}
inline reverse_iterator &operator++() { // pre-increment
if (behind_) {
if (state_ < 0) {
// operator*() called decAndRead() so p_ is already behind.
behind_ = false;
} else {
state_ = 0;
} else if (state_ == 0) {
Impl::dec(p_);
} else /* state_ > 0 */ {
// operator--() called readAndInc() so we know how far to skip.
p_ = units_.data();
state_ = 0;
}
return *this;
}
inline reverse_iterator operator++(int) { // post-increment
if (behind_) {
if (state_ < 0) {
// operator*() called decAndRead() so p_ is already behind.
reverse_iterator result(*this);
behind_ = false;
state_ = 0;
return result;
} else {
} else if (state_ == 0) {
unitsLimit_ = p_;
units_ = Impl::decAndRead(p_);
reverse_iterator result(*this);
result.behind_ = true;
// keep this->behind_ == false
result.state_ = -1;
// keep this->state_ == 0
return result;
} else /* state_ > 0 */ {
reverse_iterator result(*this);
// operator--() called readAndInc() so we know how far to skip.
p_ = units_.data();
state_ = 0;
return result;
}
}
inline reverse_iterator &operator--() { // pre-decrement
#if 0 // TODO
if (state_ > 0) {
// operator*() called readAndInc() so p_ is ahead of the logical position.
p_ = units_.data();
if (state_ < 0) {
// operator*() called decAndRead() so p_ is behind the logical position.
p_ = unitsLimit_;
}
units_ = Impl::decAndRead(p_);
state_ = -1;
#endif
units_ = Impl::readAndInc(p_);
state_ = 1;
return *this;
}
@ -1645,7 +1669,7 @@ public:
private:
inline UnitIter getLogicalPosition() const {
return !behind_ ? p_ : unitsLimit_;
return state_ >= 0 ? p_ : unitsLimit_;
}
// operator*() etc. are logically const.
@ -1653,11 +1677,13 @@ private:
// Keep state so that we call decAndRead() only once for both operator*() and ++
// to make it easy for the compiler to optimize.
mutable UnsafeCodeUnits_ units_;
// For fast getLogicalPosition() and operator==().
mutable UnitIter unitsLimit_;
// true: units_ = decAndRead(), p_ = units start
// >0: units_ = readAndInc(), p_ = units limit
// 0: initial state
// <0: units_ = decAndRead(), p_ = units start
// which means that p_ is behind its logical position
// false: initial state
mutable bool behind_ = false;
mutable int8_t state_ = 0;
};
#endif // U_IN_DOXYGEN
@ -1685,6 +1711,8 @@ public:
/** @draft ICU 78 */
UnsafeUTFStringCodePoints(const UnsafeUTFStringCodePoints &other) = default;
/** @draft ICU 78 */
UnsafeUTFStringCodePoints &operator=(const UnsafeUTFStringCodePoints &other) = default;
/** @draft ICU 78 */
@ -1697,12 +1725,18 @@ public:
return {s.data() + s.length()};
}
/** @draft ICU 78 */
/**
* @return reverse_iterator(end())
* @draft ICU 78
*/
auto rbegin() const {
return std::make_reverse_iterator(end());
}
/** @draft ICU 78 */
/**
* @return reverse_iterator(begin())
* @draft ICU 78
*/
auto rend() const {
return std::make_reverse_iterator(begin());
}