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[libc++] Simplify single-iterator __bit_iterator algorithm specializa…
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…tions

The single-iterator algorithms have an implementation for `false` and `true`, which are almost identical. Instead of writing two functions, this refactors the code to take the value searched for as a template parameter. This avoids a lot of code duplication and makes it easier to reason about the algorithm and their difference.

Reviewed By: #libc, Mordante

Spies: Mordante, libcxx-commits

Differential Revision: https://reviews.llvm.org/D156033
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@philnik777
philnik777 committed Jul 27, 2023
1 parent a800485 commit 4d20cfc
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Showing 2 changed files with 42 additions and 137 deletions.
177 changes: 41 additions & 136 deletions libcxx/include/__bit_reference
View file
Original file line number Diff line number Diff line change
Expand Up @@ -179,47 +179,18 @@ private:
__bit_const_reference& operator=(const __bit_const_reference&) = delete;
};

// find

template <class _Cp, bool _IsConst>
_LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI __bit_iterator<_Cp, _IsConst>
__find_bool_true(__bit_iterator<_Cp, _IsConst> __first, typename _Cp::size_type __n)
{
typedef __bit_iterator<_Cp, _IsConst> _It;
typedef typename _It::__storage_type __storage_type;
const int __bits_per_word = _It::__bits_per_word;
// do first partial word
if (__first.__ctz_ != 0)
{
__storage_type __clz_f = static_cast<__storage_type>(__bits_per_word - __first.__ctz_);
__storage_type __dn = _VSTD::min(__clz_f, __n);
__storage_type __m = (~__storage_type(0) << __first.__ctz_) & (~__storage_type(0) >> (__clz_f - __dn));
__storage_type __b = *__first.__seg_ & __m;
if (__b)
return _It(__first.__seg_, static_cast<unsigned>(_VSTD::__libcpp_ctz(__b)));
if (__n == __dn)
return __first + __n;
__n -= __dn;
++__first.__seg_;
}
// do middle whole words
for (; __n >= __bits_per_word; ++__first.__seg_, __n -= __bits_per_word)
if (*__first.__seg_)
return _It(__first.__seg_, static_cast<unsigned>(_VSTD::__libcpp_ctz(*__first.__seg_)));
// do last partial word
if (__n > 0)
{
__storage_type __m = ~__storage_type(0) >> (__bits_per_word - __n);
__storage_type __b = *__first.__seg_ & __m;
if (__b)
return _It(__first.__seg_, static_cast<unsigned>(_VSTD::__libcpp_ctz(__b)));
}
return _It(__first.__seg_, static_cast<unsigned>(__n));
template <bool _Invert, class _Tp>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp __invert_if(_Tp __v) {
if (_Invert)
return ~__v;
return __v;
}

template <class _Cp, bool _IsConst>
// find

template <bool _ToFind, class _Cp, bool _IsConst>
_LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI __bit_iterator<_Cp, _IsConst>
__find_bool_false(__bit_iterator<_Cp, _IsConst> __first, typename _Cp::size_type __n)
__find_bool(__bit_iterator<_Cp, _IsConst> __first, typename _Cp::size_type __n)
{
typedef __bit_iterator<_Cp, _IsConst> _It;
typedef typename _It::__storage_type __storage_type;
Expand All @@ -230,7 +201,7 @@ __find_bool_false(__bit_iterator<_Cp, _IsConst> __first, typename _Cp::size_type
__storage_type __clz_f = static_cast<__storage_type>(__bits_per_word - __first.__ctz_);
__storage_type __dn = _VSTD::min(__clz_f, __n);
__storage_type __m = (~__storage_type(0) << __first.__ctz_) & (~__storage_type(0) >> (__clz_f - __dn));
__storage_type __b = ~*__first.__seg_ & __m;
__storage_type __b = std::__invert_if<!_ToFind>(*__first.__seg_) & __m;
if (__b)
return _It(__first.__seg_, static_cast<unsigned>(_VSTD::__libcpp_ctz(__b)));
if (__n == __dn)
Expand All @@ -239,17 +210,16 @@ __find_bool_false(__bit_iterator<_Cp, _IsConst> __first, typename _Cp::size_type
++__first.__seg_;
}
// do middle whole words
for (; __n >= __bits_per_word; ++__first.__seg_, __n -= __bits_per_word)
{
__storage_type __b = ~*__first.__seg_;
for (; __n >= __bits_per_word; ++__first.__seg_, __n -= __bits_per_word) {
__storage_type __b = std::__invert_if<!_ToFind>(*__first.__seg_);
if (__b)
return _It(__first.__seg_, static_cast<unsigned>(_VSTD::__libcpp_ctz(__b)));
}
// do last partial word
if (__n > 0)
{
__storage_type __m = ~__storage_type(0) >> (__bits_per_word - __n);
__storage_type __b = ~*__first.__seg_ & __m;
__storage_type __b = std::__invert_if<!_ToFind>(*__first.__seg_) & __m;
if (__b)
return _It(__first.__seg_, static_cast<unsigned>(_VSTD::__libcpp_ctz(__b)));
}
Expand All @@ -262,15 +232,15 @@ __bit_iterator<_Cp, _IsConst>
find(__bit_iterator<_Cp, _IsConst> __first, __bit_iterator<_Cp, _IsConst> __last, const _Tp& __value)
{
if (static_cast<bool>(__value))
return _VSTD::__find_bool_true(__first, static_cast<typename _Cp::size_type>(__last - __first));
return _VSTD::__find_bool_false(__first, static_cast<typename _Cp::size_type>(__last - __first));
return _VSTD::__find_bool<true>(__first, static_cast<typename _Cp::size_type>(__last - __first));
return _VSTD::__find_bool<false>(__first, static_cast<typename _Cp::size_type>(__last - __first));
}

// count

template <class _Cp, bool _IsConst>
template <bool _ToCount, class _Cp, bool _IsConst>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 typename __bit_iterator<_Cp, _IsConst>::difference_type
__count_bool_true(__bit_iterator<_Cp, _IsConst> __first, typename _Cp::size_type __n)
__count_bool(__bit_iterator<_Cp, _IsConst> __first, typename _Cp::size_type __n)
{
typedef __bit_iterator<_Cp, _IsConst> _It;
typedef typename _It::__storage_type __storage_type;
Expand All @@ -283,49 +253,18 @@ __count_bool_true(__bit_iterator<_Cp, _IsConst> __first, typename _Cp::size_type
__storage_type __clz_f = static_cast<__storage_type>(__bits_per_word - __first.__ctz_);
__storage_type __dn = _VSTD::min(__clz_f, __n);
__storage_type __m = (~__storage_type(0) << __first.__ctz_) & (~__storage_type(0) >> (__clz_f - __dn));
__r = _VSTD::__libcpp_popcount(*__first.__seg_ & __m);
__r = _VSTD::__libcpp_popcount(std::__invert_if<!_ToCount>(*__first.__seg_) & __m);
__n -= __dn;
++__first.__seg_;
}
// do middle whole words
for (; __n >= __bits_per_word; ++__first.__seg_, __n -= __bits_per_word)
__r += _VSTD::__libcpp_popcount(*__first.__seg_);
__r += _VSTD::__libcpp_popcount(std::__invert_if<!_ToCount>(*__first.__seg_));
// do last partial word
if (__n > 0)
{
__storage_type __m = ~__storage_type(0) >> (__bits_per_word - __n);
__r += _VSTD::__libcpp_popcount(*__first.__seg_ & __m);
}
return __r;
}

template <class _Cp, bool _IsConst>
_LIBCPP_HIDE_FROM_ABI typename __bit_iterator<_Cp, _IsConst>::difference_type
__count_bool_false(__bit_iterator<_Cp, _IsConst> __first, typename _Cp::size_type __n)
{
typedef __bit_iterator<_Cp, _IsConst> _It;
typedef typename _It::__storage_type __storage_type;
typedef typename _It::difference_type difference_type;
const int __bits_per_word = _It::__bits_per_word;
difference_type __r = 0;
// do first partial word
if (__first.__ctz_ != 0)
{
__storage_type __clz_f = static_cast<__storage_type>(__bits_per_word - __first.__ctz_);
__storage_type __dn = _VSTD::min(__clz_f, __n);
__storage_type __m = (~__storage_type(0) << __first.__ctz_) & (~__storage_type(0) >> (__clz_f - __dn));
__r = _VSTD::__libcpp_popcount(~*__first.__seg_ & __m);
__n -= __dn;
++__first.__seg_;
}
// do middle whole words
for (; __n >= __bits_per_word; ++__first.__seg_, __n -= __bits_per_word)
__r += _VSTD::__libcpp_popcount(~*__first.__seg_);
// do last partial word
if (__n > 0)
{
__storage_type __m = ~__storage_type(0) >> (__bits_per_word - __n);
__r += _VSTD::__libcpp_popcount(~*__first.__seg_ & __m);
__r += _VSTD::__libcpp_popcount(std::__invert_if<!_ToCount>(*__first.__seg_) & __m);
}
return __r;
}
Expand All @@ -336,45 +275,15 @@ typename __bit_iterator<_Cp, _IsConst>::difference_type
count(__bit_iterator<_Cp, _IsConst> __first, __bit_iterator<_Cp, _IsConst> __last, const _Tp& __value)
{
if (static_cast<bool>(__value))
return _VSTD::__count_bool_true(__first, static_cast<typename _Cp::size_type>(__last - __first));
return _VSTD::__count_bool_false(__first, static_cast<typename _Cp::size_type>(__last - __first));
return _VSTD::__count_bool<true>(__first, static_cast<typename _Cp::size_type>(__last - __first));
return _VSTD::__count_bool<false>(__first, static_cast<typename _Cp::size_type>(__last - __first));
}

// fill_n

template <class _Cp>
_LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void
__fill_n_false(__bit_iterator<_Cp, false> __first, typename _Cp::size_type __n)
{
typedef __bit_iterator<_Cp, false> _It;
typedef typename _It::__storage_type __storage_type;
const int __bits_per_word = _It::__bits_per_word;
// do first partial word
if (__first.__ctz_ != 0)
{
__storage_type __clz_f = static_cast<__storage_type>(__bits_per_word - __first.__ctz_);
__storage_type __dn = _VSTD::min(__clz_f, __n);
__storage_type __m = (~__storage_type(0) << __first.__ctz_) & (~__storage_type(0) >> (__clz_f - __dn));
*__first.__seg_ &= ~__m;
__n -= __dn;
++__first.__seg_;
}
// do middle whole words
__storage_type __nw = __n / __bits_per_word;
std::fill_n(std::__to_address(__first.__seg_), __nw, 0);
__n -= __nw * __bits_per_word;
// do last partial word
if (__n > 0)
{
__first.__seg_ += __nw;
__storage_type __m = ~__storage_type(0) >> (__bits_per_word - __n);
*__first.__seg_ &= ~__m;
}
}

template <class _Cp>
template <bool _FillValue, class _Cp>
_LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void
__fill_n_true(__bit_iterator<_Cp, false> __first, typename _Cp::size_type __n)
__fill_n(__bit_iterator<_Cp, false> __first, typename _Cp::size_type __n)
{
typedef __bit_iterator<_Cp, false> _It;
typedef typename _It::__storage_type __storage_type;
Expand All @@ -385,21 +294,26 @@ __fill_n_true(__bit_iterator<_Cp, false> __first, typename _Cp::size_type __n)
__storage_type __clz_f = static_cast<__storage_type>(__bits_per_word - __first.__ctz_);
__storage_type __dn = _VSTD::min(__clz_f, __n);
__storage_type __m = (~__storage_type(0) << __first.__ctz_) & (~__storage_type(0) >> (__clz_f - __dn));
*__first.__seg_ |= __m;
if (_FillValue)
*__first.__seg_ |= __m;
else
*__first.__seg_ &= ~__m;
__n -= __dn;
++__first.__seg_;
}
// do middle whole words
__storage_type __nw = __n / __bits_per_word;
// __storage_type is always an unsigned type, so -1 sets all bits
std::fill_n(std::__to_address(__first.__seg_), __nw, static_cast<__storage_type>(-1));
std::fill_n(std::__to_address(__first.__seg_), __nw, _FillValue ? static_cast<__storage_type>(-1) : 0);
__n -= __nw * __bits_per_word;
// do last partial word
if (__n > 0)
{
__first.__seg_ += __nw;
__storage_type __m = ~__storage_type(0) >> (__bits_per_word - __n);
*__first.__seg_ |= __m;
if (_FillValue)
*__first.__seg_ |= __m;
else
*__first.__seg_ &= ~__m;
}
}

Expand All @@ -411,9 +325,9 @@ fill_n(__bit_iterator<_Cp, false> __first, typename _Cp::size_type __n, bool __v
if (__n > 0)
{
if (__value)
_VSTD::__fill_n_true(__first, __n);
_VSTD::__fill_n<true>(__first, __n);
else
_VSTD::__fill_n_false(__first, __n);
_VSTD::__fill_n<false>(__first, __n);
}
}

Expand Down Expand Up @@ -1276,13 +1190,9 @@ private:
friend class __bit_const_reference<_Cp>;
friend class __bit_iterator<_Cp, true>;
template <class _Dp> friend struct __bit_array;
template <class _Dp>
template <bool _FillValue, class _Dp>
_LIBCPP_CONSTEXPR_SINCE_CXX20
friend void __fill_n_false(__bit_iterator<_Dp, false> __first, typename _Dp::size_type __n);

template <class _Dp>
_LIBCPP_CONSTEXPR_SINCE_CXX20
friend void __fill_n_true(__bit_iterator<_Dp, false> __first, typename _Dp::size_type __n);
friend void __fill_n(__bit_iterator<_Dp, false> __first, typename _Dp::size_type __n);

template <class _Dp, bool _IC>
_LIBCPP_CONSTEXPR_SINCE_CXX20
Expand Down Expand Up @@ -1343,17 +1253,12 @@ private:
friend bool equal(__bit_iterator<_Dp, _IC1>,
__bit_iterator<_Dp, _IC1>,
__bit_iterator<_Dp, _IC2>);
template <class _Dp, bool _IC>
_LIBCPP_CONSTEXPR_SINCE_CXX20
friend __bit_iterator<_Dp, _IC> __find_bool_true(__bit_iterator<_Dp, _IC>, typename _Dp::size_type);
template <class _Dp, bool _IC>
template <bool _ToFind, class _Dp, bool _IC>
_LIBCPP_CONSTEXPR_SINCE_CXX20
friend __bit_iterator<_Dp, _IC> __find_bool_false(__bit_iterator<_Dp, _IC>, typename _Dp::size_type);
template <class _Dp, bool _IC> friend typename __bit_iterator<_Dp, _IC>::difference_type
friend __bit_iterator<_Dp, _IC> __find_bool(__bit_iterator<_Dp, _IC>, typename _Dp::size_type);
template <bool _ToCount, class _Dp, bool _IC> friend typename __bit_iterator<_Dp, _IC>::difference_type
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23
__count_bool_true(__bit_iterator<_Dp, _IC>, typename _Dp::size_type);
template <class _Dp, bool _IC> friend typename __bit_iterator<_Dp, _IC>::difference_type
__count_bool_false(__bit_iterator<_Dp, _IC>, typename _Dp::size_type);
__count_bool(__bit_iterator<_Dp, _IC>, typename _Dp::size_type);
};

_LIBCPP_END_NAMESPACE_STD
Expand Down
2 changes: 1 addition & 1 deletion libcxx/include/bitset
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1012,7 +1012,7 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23
size_t
bitset<_Size>::count() const _NOEXCEPT
{
return static_cast<size_t>(_VSTD::__count_bool_true(base::__make_iter(0), _Size));
return static_cast<size_t>(_VSTD::__count_bool<true>(base::__make_iter(0), _Size));
}

template <size_t _Size>
Expand Down

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