[libc-commits] [libc] [libc][support][UInt] implement 128b math helpers (PR #86531)
Nick Desaulniers via libc-commits
libc-commits at lists.llvm.org
Mon Mar 25 10:34:48 PDT 2024
https://github.com/nickdesaulniers updated https://github.com/llvm/llvm-project/pull/86531
>From 3d400c64eb04e0ce52054befb1af8d89f1bb477e Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers at google.com>
Date: Mon, 25 Mar 2024 09:51:29 -0700
Subject: [PATCH 1/3] [libc][support][UInt] implement 128b popcount
We could have used this in the implementation of UInt::has_single_bit, but
has_single_bit has a perhaps useful early return.
---
libc/src/__support/UInt.h | 11 +++++++++++
libc/test/src/__support/CPP/bit_test.cpp | 9 +--------
2 files changed, 12 insertions(+), 8 deletions(-)
diff --git a/libc/src/__support/UInt.h b/libc/src/__support/UInt.h
index df01e081e3c19e..b04e8d02ad4c16 100644
--- a/libc/src/__support/UInt.h
+++ b/libc/src/__support/UInt.h
@@ -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>
diff --git a/libc/test/src/__support/CPP/bit_test.cpp b/libc/test/src/__support/CPP/bit_test.cpp
index cee5b90c8f4bdb..875b47e6a1980e 100644
--- a/libc/test/src/__support/CPP/bit_test.cpp
+++ b/libc/test/src/__support/CPP/bit_test.cpp
@@ -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,
@@ -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),
>From 457a41d5c31becc23558149231db5fd25492397a Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers at google.com>
Date: Mon, 25 Mar 2024 10:08:43 -0700
Subject: [PATCH 2/3] fixup math extras
---
libc/src/__support/UInt.h | 43 ++++++++++++++++++++
libc/test/src/__support/math_extras_test.cpp | 4 +-
2 files changed, 45 insertions(+), 2 deletions(-)
diff --git a/libc/src/__support/UInt.h b/libc/src/__support/UInt.h
index b04e8d02ad4c16..282efdba1c5f2b 100644
--- a/libc/src/__support/UInt.h
+++ b/libc/src/__support/UInt.h
@@ -1229,6 +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
diff --git a/libc/test/src/__support/math_extras_test.cpp b/libc/test/src/__support/math_extras_test.cpp
index e642248881a41c..e88b3e1d6b687b 100644
--- a/libc/test/src/__support/math_extras_test.cpp
+++ b/libc/test/src/__support/math_extras_test.cpp
@@ -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"
@@ -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>()));
>From b1e40ede9fd2cd33c7f533147827b23541c516c9 Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers at google.com>
Date: Mon, 25 Mar 2024 10:28:50 -0700
Subject: [PATCH 3/3] utilize __builtin_popcountg
---
libc/src/__support/CPP/bit.h | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/libc/src/__support/CPP/bit.h b/libc/src/__support/CPP/bit.h
index 3f2fbec944054c..526c499adc374c 100644
--- a/libc/src/__support/CPP/bit.h
+++ b/libc/src/__support/CPP/bit.h
@@ -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)
+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) {
@@ -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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