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[libc][support][UInt] implement 128b math helpers #86531

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Merged
merged 3 commits into from
Mar 27, 2024
Merged

[libc][support][UInt] implement 128b math helpers #86531

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3d400c6
[libc][support][UInt] implement 128b popcount
nickdesaulniers Mar 25, 2024
457a41d
fixup math extras
nickdesaulniers Mar 25, 2024
b1e40ed
utilize __builtin_popcountg
nickdesaulniers Mar 25, 2024
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10 changes: 9 additions & 1 deletion libc/src/__support/CPP/bit.h
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Original file line number Diff line number Diff line change
Expand Up @@ -242,6 +242,14 @@ LIBC_INLINE constexpr To bit_or_static_cast(const From &from) {
/// Count number of 1's aka population count or Hamming weight.
///
/// Only unsigned integral types are allowed.
// clang-19+, gcc-14+
#if __has_builtin(__builtin_popcountg)
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Ah, should this be using LIBC_HAS_BUILTIN?

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gcc-10+ supports __has_builtin. While wrapping the use of __has_builtin used to be necessary to support older compilers, this is no longer necessary since we only support gcc-12+ . https://libc.llvm.org/compiler_support.html I'll leave this out, and file a bug about removing it.

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Filed #86546

template <typename T>
[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
popcount(T value) {
return __builtin_popcountg(value);
}
#else // !__has_builtin(__builtin_popcountg)
template <typename T>
[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
popcount(T value) {
Expand All @@ -261,7 +269,7 @@ ADD_SPECIALIZATION(unsigned short, __builtin_popcount)
ADD_SPECIALIZATION(unsigned, __builtin_popcount)
ADD_SPECIALIZATION(unsigned long, __builtin_popcountl)
ADD_SPECIALIZATION(unsigned long long, __builtin_popcountll)
// TODO: 128b specializations?
#endif // __builtin_popcountg
#undef ADD_SPECIALIZATION

} // namespace LIBC_NAMESPACE::cpp
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54 changes: 54 additions & 0 deletions libc/src/__support/UInt.h
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Expand Up @@ -1082,6 +1082,17 @@ bit_cast(const UInt<Bits> &from) {
return cpp::bit_cast<To>(from.val);
}

// Specialization of cpp::popcount ('bit.h') for BigInt.
template <typename T>
[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<is_big_int_v<T>, int>
popcount(T value) {
int bits = 0;
for (auto word : value.val)
if (word)
bits += popcount(word);
return bits;
}

// Specialization of cpp::has_single_bit ('bit.h') for BigInt.
template <typename T>
[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<is_big_int_v<T>, bool>
Expand Down Expand Up @@ -1218,6 +1229,49 @@ LIBC_INLINE constexpr cpp::enable_if_t<is_big_int_v<T>, T> mask_leading_ones() {
return out;
}

// Specialization of count_zeros ('math_extras.h') for BigInt.
template <typename T>
[[nodiscard]]
LIBC_INLINE constexpr cpp::enable_if_t<is_big_int_v<T>, int>
count_zeros(T value) {
return cpp::popcount(~value);
}

// Specialization of first_leading_zero ('math_extras.h') for BigInt.
template <typename T>
[[nodiscard]]
LIBC_INLINE constexpr cpp::enable_if_t<is_big_int_v<T>, int>
first_leading_zero(T value) {
return value == cpp::numeric_limits<T>::max() ? 0
: cpp::countl_one(value) + 1;
}

// Specialization of first_leading_one ('math_extras.h') for BigInt.
template <typename T>
[[nodiscard]]
LIBC_INLINE constexpr cpp::enable_if_t<is_big_int_v<T>, int>
first_leading_one(T value) {
return first_leading_zero(~value);
}

// Specialization of first_trailing_zero ('math_extras.h') for BigInt.
template <typename T>
[[nodiscard]]
LIBC_INLINE constexpr cpp::enable_if_t<is_big_int_v<T>, int>
first_trailing_zero(T value) {
return value == cpp::numeric_limits<T>::max() ? 0
: cpp::countr_zero(~value) + 1;
}

// Specialization of first_trailing_one ('math_extras.h') for BigInt.
template <typename T>
[[nodiscard]]
LIBC_INLINE constexpr cpp::enable_if_t<is_big_int_v<T>, int>
first_trailing_one(T value) {
return value == cpp::numeric_limits<T>::max() ? 0
: cpp::countr_zero(value) + 1;
}

} // namespace LIBC_NAMESPACE

#endif // LLVM_LIBC_SRC___SUPPORT_UINT_H
9 changes: 1 addition & 8 deletions libc/test/src/__support/CPP/bit_test.cpp
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Expand Up @@ -15,13 +15,6 @@

namespace LIBC_NAMESPACE::cpp {

using UnsignedTypesNoBigInt = testing::TypeList<
#if defined(LIBC_TYPES_HAS_INT128)
__uint128_t,
#endif // LIBC_TYPES_HAS_INT128
unsigned char, unsigned short, unsigned int, unsigned long,
unsigned long long>;

using UnsignedTypes = testing::TypeList<
#if defined(LIBC_TYPES_HAS_INT128)
__uint128_t,
Expand Down Expand Up @@ -228,7 +221,7 @@ TEST(LlvmLibcBitTest, Rotr) {
rotr<uint64_t>(0x12345678deadbeefULL, -19));
}

TYPED_TEST(LlvmLibcBitTest, CountOnes, UnsignedTypesNoBigInt) {
TYPED_TEST(LlvmLibcBitTest, CountOnes, UnsignedTypes) {
EXPECT_EQ(popcount(T(0)), 0);
for (int i = 0; i != cpp::numeric_limits<T>::digits; ++i)
EXPECT_EQ(popcount<T>(cpp::numeric_limits<T>::max() >> i),
Expand Down
4 changes: 2 additions & 2 deletions libc/test/src/__support/math_extras_test.cpp
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Expand Up @@ -6,7 +6,7 @@
//
//===----------------------------------------------------------------------===//

#include "src/__support/UInt128.h" // UInt128
#include "src/__support/UInt128.h" // UInt<128>
#include "src/__support/integer_literals.h"
#include "src/__support/math_extras.h"
#include "test/UnitTest/Test.h"
Expand All @@ -19,7 +19,7 @@ using UnsignedTypesNoBigInt = testing::TypeList<
__uint128_t,
#endif // LIBC_TYPES_HAS_INT128
unsigned char, unsigned short, unsigned int, unsigned long,
unsigned long long>;
unsigned long long, UInt<128>>;

TEST(LlvmLibcBlockMathExtrasTest, mask_trailing_ones) {
EXPECT_EQ(0_u8, (mask_leading_ones<uint8_t, 0>()));
Expand Down