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🎨 Refactor field to use stdx::bit_mask
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Simplified `bits_locator_t::insert` a little: two compile-time cases can be
collapsed into one.
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@bdeane-intel
bdeane-intel committed Mar 21, 2024
1 parent 570a09e commit 4c8f1f6
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Showing 2 changed files with 30 additions and 46 deletions.
2 changes: 1 addition & 1 deletion CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -29,7 +29,7 @@ add_versioned_package(
OPTIONS
"FMT_INSTALL OFF"
"FMT_OS OFF")
add_versioned_package("gh:intel/cpp-std-extensions#9a49ddd")
add_versioned_package("gh:intel/cpp-std-extensions#cff7a15")
add_versioned_package("gh:intel/cpp-baremetal-concurrency#8d49b6d")

add_library(cib INTERFACE)
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74 changes: 29 additions & 45 deletions include/msg/field.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -72,19 +72,6 @@ concept field_location = requires(T const &t) {
};

namespace detail {
template <typename T> CONSTEVAL auto bit_size() { return sizeof(T) * CHAR_BIT; }

template <std::unsigned_integral T, auto BitSize = bit_size<T>()>
requires(BitSize <= bit_size<T>())
CONSTEVAL auto bit_mask() -> T {
if constexpr (BitSize == 0u) {
return {};
} else {
return static_cast<T>(std::numeric_limits<T>::max() >>
(bit_size<T>() - BitSize));
}
}

template <typename Name, typename T, std::uint32_t BitSize>
struct field_spec_t {
using type = T;
Expand All @@ -100,7 +87,7 @@ struct bits_locator_t {

template <std::unsigned_integral T>
[[nodiscard]] constexpr static auto fold(T value) -> T {
if constexpr (BitSize == bit_size<T>()) {
if constexpr (BitSize == stdx::bit_size<T>()) {
return {};
} else {
return static_cast<T>(value >> BitSize);
Expand All @@ -109,7 +96,7 @@ struct bits_locator_t {

template <std::unsigned_integral T>
[[nodiscard]] constexpr static auto unfold(T value) -> T {
if constexpr (BitSize == bit_size<T>()) {
if constexpr (BitSize == stdx::bit_size<T>()) {
return {};
} else {
return static_cast<T>(value << BitSize);
Expand All @@ -125,7 +112,7 @@ struct bits_locator_t {
constexpr auto BaseIndex =
DWordIndex * sizeof(std::uint32_t) / sizeof(elem_t);

constexpr auto elem_size = bit_size<elem_t>();
constexpr auto elem_size = stdx::bit_size<elem_t>();
constexpr auto max_idx = BaseIndex + Msb / elem_size;
constexpr auto min_idx = BaseIndex + Lsb / elem_size;

Expand All @@ -135,7 +122,7 @@ struct bits_locator_t {
constexpr auto current_idx = BaseIndex + CurrentMsb / elem_size;
if constexpr (current_idx == max_idx and current_idx == min_idx) {
constexpr auto mask =
bit_mask<T, CurrentMsb % elem_size + 1u>();
stdx::bit_mask<T, CurrentMsb % elem_size>();
constexpr auto shift = Lsb % elem_size;
return (std::forward<Rng>(rng)[current_idx] & mask) >> shift;
} else if constexpr (current_idx == min_idx) {
Expand All @@ -144,7 +131,7 @@ struct bits_locator_t {
return value | (std::forward<Rng>(rng)[current_idx] >> shift);
} else if constexpr (current_idx == max_idx) {
constexpr auto mask =
bit_mask<T, CurrentMsb % elem_size + 1u>();
stdx::bit_mask<T, CurrentMsb % elem_size>();
constexpr auto NewMsb =
(CurrentMsb / elem_size) * elem_size - 1u;
MUSTTAIL return recurse.template operator()<NewMsb>(
Expand All @@ -171,47 +158,44 @@ struct bits_locator_t {
constexpr auto BaseIndex =
DWordIndex * sizeof(std::uint32_t) / sizeof(elem_t);

constexpr auto elem_size = bit_size<elem_t>();
constexpr auto max_idx = BaseIndex + Msb / elem_size;
constexpr auto min_idx = BaseIndex + Lsb / elem_size;
constexpr auto elem_size = stdx::bit_size<elem_t>();
[[maybe_unused]] constexpr auto min_idx = BaseIndex + Lsb / elem_size;
[[maybe_unused]] constexpr auto max_idx = BaseIndex + Msb / elem_size;

constexpr auto f =
[]<auto CurrentLsb, typename Rng>([[maybe_unused]] auto recurse,
Rng &&rng, T value) -> void {
constexpr auto current_idx = BaseIndex + CurrentLsb / elem_size;

if constexpr (current_idx == max_idx and current_idx == min_idx) {
constexpr auto shift = CurrentLsb % elem_size;
constexpr auto numbits = Msb - CurrentLsb + 1u;
constexpr auto value_mask = bit_mask<elem_t, numbits>()
<< shift;
constexpr auto leftover_mask = ~value_mask;
if constexpr (current_idx == max_idx) {
constexpr auto lsb = CurrentLsb % elem_size;
constexpr auto msb = Msb % elem_size;
constexpr auto leftover_mask =
~stdx::bit_mask<elem_t, msb, lsb>();

auto &elem = std::forward<Rng>(rng)[current_idx];
elem &= leftover_mask;
elem |= static_cast<elem_t>(value << shift);
elem |= static_cast<elem_t>(value << lsb);
} else if constexpr (current_idx == min_idx) {
constexpr auto shift = CurrentLsb % elem_size;
constexpr auto numbits = elem_size - shift;
constexpr auto value_mask = bit_mask<elem_t, numbits>();
constexpr auto leftover_mask = bit_mask<elem_t, shift>();
constexpr auto lsb = CurrentLsb % elem_size;
constexpr auto numbits = elem_size - lsb;
constexpr auto value_mask =
stdx::bit_mask<elem_t, numbits - 1>();
constexpr auto leftover_mask = ~(value_mask << lsb);

auto &elem = std::forward<Rng>(rng)[current_idx];
elem &= leftover_mask;
elem |= static_cast<elem_t>((value & value_mask) << shift);
elem |= static_cast<elem_t>((value & value_mask) << lsb);

constexpr auto NewLsb = CurrentLsb + numbits;
MUSTTAIL return recurse.template operator()<NewLsb>(
recurse, std::forward<Rng>(rng), value >> numbits);
} else if constexpr (current_idx == max_idx) {
constexpr auto numbits = Msb - CurrentLsb + 1u;
constexpr auto value_mask = bit_mask<elem_t, numbits>();
constexpr auto leftover_mask = ~value_mask;

auto &elem = std::forward<Rng>(rng)[current_idx];
elem &= leftover_mask;
elem |= static_cast<elem_t>(value);
} else {
constexpr auto value_mask = bit_mask<elem_t, elem_size>();
constexpr auto value_mask = stdx::bit_mask<elem_t>();

auto &elem = std::forward<Rng>(rng)[current_idx];
elem = value & value_mask;

constexpr auto NewLsb = CurrentLsb + elem_size;
MUSTTAIL return recurse.template operator()<NewLsb>(
recurse, std::forward<Rng>(rng), value >> elem_size);
Expand Down Expand Up @@ -272,7 +256,7 @@ template <bits_locator... BLs> struct field_locator_t {
auto const insert_bits = [&]<bits_locator B>() {
B::insert(
std::forward<R>(r),
static_cast<raw_t>(raw & detail::bit_mask<raw_t, B::size>()));
static_cast<raw_t>(raw & stdx::bit_mask<raw_t, B::size - 1>()));
raw = B::fold(raw);
};

Expand Down Expand Up @@ -378,7 +362,7 @@ class field_t : public field_spec_t<Name, T, detail::field_size<Ats...>>,
}
static_assert((... and Ats.valid()),
"Individual field location size cannot exceed 64 bits!");
static_assert(detail::bit_size<T>() >= (0u + ... + Ats.size()),
static_assert(stdx::bit_size<T>() >= (0u + ... + Ats.size()),
"Field size is smaller than sum of locations!");

public:
Expand All @@ -399,7 +383,7 @@ class field_t : public field_spec_t<Name, T, detail::field_size<Ats...>>,

template <typename DataType> constexpr static auto fits_inside() -> bool {
constexpr auto bits_capacity =
detail::bit_size<typename DataType::value_type>() *
stdx::bit_size<typename DataType::value_type>() *
stdx::ct_capacity_v<DataType>;
return locator_t::template fits_inside<bits_capacity>();
}
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