Skip to content

Rotate bits using intrinsics #2369

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
Stephan T. Lavavej (StephanTLavavej) merged 3 commits into from
Dec 9, 2021
Merged

Rotate bits using intrinsics #2369

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
1603faf
make sure we are rotating in the right direction
AlexGuteniev Dec 1, 2021
bf7b413
Some intrinsics
AlexGuteniev Dec 1, 2021
b05e2e9
simplify test
AlexGuteniev Dec 1, 2021
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
24 changes: 22 additions & 2 deletions stl/inc/bit
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -92,7 +92,17 @@ _NODISCARD constexpr _Ty rotr(_Ty _Val, int _Rotation) noexcept;
template <class _Ty, enable_if_t<_Is_standard_unsigned_integer<_Ty>, int> = 0>
_NODISCARD constexpr _Ty rotl(const _Ty _Val, const int _Rotation) noexcept {
constexpr auto _Digits = numeric_limits<_Ty>::digits;
const auto _Remainder = _Rotation % _Digits;

if (!_STD is_constant_evaluated()) {
if constexpr (_Digits == 64) {
return _rotl64(_Val, _Rotation);
} else if constexpr (_Digits == 32) {
return _rotl(_Val, _Rotation);
}
// TRANSITION: fallback to non-intrinsic case until <intrin0.h> changes
}

const auto _Remainder = _Rotation % _Digits;
if (_Remainder > 0) {
return static_cast<_Ty>(
static_cast<_Ty>(_Val << _Remainder) | static_cast<_Ty>(_Val >> (_Digits - _Remainder)));
Expand All @@ -106,7 +116,17 @@ _NODISCARD constexpr _Ty rotl(const _Ty _Val, const int _Rotation) noexcept {
template <class _Ty, enable_if_t<_Is_standard_unsigned_integer<_Ty>, int> _Enabled>
Comment thread
AlexGuteniev marked this conversation as resolved.
_NODISCARD constexpr _Ty rotr(const _Ty _Val, const int _Rotation) noexcept {
constexpr auto _Digits = numeric_limits<_Ty>::digits;
const auto _Remainder = _Rotation % _Digits;

if (!_STD is_constant_evaluated()) {
if constexpr (_Digits == 64) {
return _rotr64(_Val, _Rotation);
} else if constexpr (_Digits == 32) {
return _rotr(_Val, _Rotation);
}
// TRANSITION: fallback to non-intrinsic case until <intrin0.h> changes
}

const auto _Remainder = _Rotation % _Digits;
if (_Remainder > 0) {
return static_cast<_Ty>(
static_cast<_Ty>(_Val >> _Remainder) | static_cast<_Ty>(_Val << (_Digits - _Remainder)));
Expand Down
24 changes: 24 additions & 0 deletions tests/std/tests/P0553R4_bit_rotating_and_counting_functions/test.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -86,9 +86,21 @@ template <typename T>
constexpr bool test_rotl() {
constexpr int digits = numeric_limits<T>::digits;
constexpr auto maxval = numeric_limits<T>::max();

constexpr T every_fourth[4] = {
static_cast<T>(0x1111'1111'1111'1111ULL),
static_cast<T>(0x2222'2222'2222'2222ULL),
static_cast<T>(0x4444'4444'4444'4444ULL),
static_cast<T>(0x8888'8888'8888'8888ULL),
};

for (int i = 0; i < digits * 2; ++i) {
assert(rotl(maxval, i) == maxval);
assert(rotl(T{0}, i) == 0);

for (int j = 0; j < 4; ++j) {
assert(rotl(every_fourth[j], i) == every_fourth[(i + j) % 4]);
}
}
return true;
}
Expand All @@ -97,9 +109,21 @@ template <typename T>
constexpr bool test_rotr() {
constexpr int digits = numeric_limits<T>::digits;
constexpr auto maxval = numeric_limits<T>::max();

constexpr T every_fourth[4] = {
static_cast<T>(0x1111'1111'1111'1111ULL),
static_cast<T>(0x2222'2222'2222'2222ULL),
static_cast<T>(0x4444'4444'4444'4444ULL),
static_cast<T>(0x8888'8888'8888'8888ULL),
};

for (int i = 0; i < digits * 2; ++i) {
assert(rotr(maxval, i) == maxval);
assert(rotr(T{0}, i) == 0);

for (int j = 0; j < 4; ++j) {
assert(rotr(every_fourth[(i + j) % 4], i) == every_fourth[j]);
}
}
return true;
}
Expand Down