[libc] rename cpp::count_ones to cpp::popcount to better mirror std::

[nickdesaulniers]

libc/src/__support/CPP/bit.h and cpp:: is meant to mirror std::. Fix the TODO.

[llvmbot]

@llvm/pr-subscribers-libc

Author: Nick Desaulniers (nickdesaulniers)

Changes

libc/src/__support/CPP/bit.h and cpp:: is meant to mirror std::. Fix the TODO.

---

Full diff: https://github.com/llvm/llvm-project/pull/84388.diff

6 Files Affected:

• (modified) libc/src/__support/CPP/bit.h (+4-6)
• (modified) libc/src/stdbit/stdc_count_ones_uc.cpp (+1-1)
• (modified) libc/src/stdbit/stdc_count_ones_ui.cpp (+1-1)
• (modified) libc/src/stdbit/stdc_count_ones_ul.cpp (+1-1)
• (modified) libc/src/stdbit/stdc_count_ones_ull.cpp (+1-1)
• (modified) libc/src/stdbit/stdc_count_ones_us.cpp (+1-1)

diff --git a/libc/src/__support/CPP/bit.h b/libc/src/__support/CPP/bit.h
index 6b625b0c97a365..015a55cc53a214 100644
--- a/libc/src/__support/CPP/bit.h
+++ b/libc/src/__support/CPP/bit.h
@@ -269,14 +269,12 @@ first_trailing_one(T value) {
   return value == cpp::numeric_limits<T>::max() ? 0 : countr_zero(value) + 1;
 }
 
-/// Count number of 1's aka population count or hamming weight.
+/// Count number of 1's aka population count or Hamming weight.
 ///
 /// Only unsigned integral types are allowed.
-// TODO: rename as 'popcount' to follow the standard
-// https://en.cppreference.com/w/cpp/numeric/popcount
 template <typename T>
 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
-count_ones(T value) {
+popcount(T value) {
   int count = 0;
   for (int i = 0; i != cpp::numeric_limits<T>::digits; ++i)
     if ((value >> i) & 0x1)
@@ -285,7 +283,7 @@ count_ones(T value) {
 }
 #define ADD_SPECIALIZATION(TYPE, BUILTIN)                                      \
   template <>                                                                  \
-  [[nodiscard]] LIBC_INLINE constexpr int count_ones<TYPE>(TYPE value) {       \
+  [[nodiscard]] LIBC_INLINE constexpr int popcount<TYPE>(TYPE value) {       \
     return BUILTIN(value);                                                     \
   }
 ADD_SPECIALIZATION(unsigned char, __builtin_popcount)
@@ -300,7 +298,7 @@ ADD_SPECIALIZATION(unsigned long long, __builtin_popcountll)
 template <typename T>
 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
 count_zeros(T value) {
-  return count_ones<T>(static_cast<T>(~value));
+  return popcount<T>(static_cast<T>(~value));
 }
 
 } // namespace LIBC_NAMESPACE::cpp
diff --git a/libc/src/stdbit/stdc_count_ones_uc.cpp b/libc/src/stdbit/stdc_count_ones_uc.cpp
index 5a7314caa3baa0..1e998ff521b7db 100644
--- a/libc/src/stdbit/stdc_count_ones_uc.cpp
+++ b/libc/src/stdbit/stdc_count_ones_uc.cpp
@@ -14,7 +14,7 @@
 namespace LIBC_NAMESPACE {
 
 LLVM_LIBC_FUNCTION(unsigned, stdc_count_ones_uc, (unsigned char value)) {
-  return static_cast<unsigned>(cpp::count_ones(value));
+  return static_cast<unsigned>(cpp::popcount(value));
 }
 
 } // namespace LIBC_NAMESPACE
diff --git a/libc/src/stdbit/stdc_count_ones_ui.cpp b/libc/src/stdbit/stdc_count_ones_ui.cpp
index 289f4bac31f7b8..e457dd793db33d 100644
--- a/libc/src/stdbit/stdc_count_ones_ui.cpp
+++ b/libc/src/stdbit/stdc_count_ones_ui.cpp
@@ -14,7 +14,7 @@
 namespace LIBC_NAMESPACE {
 
 LLVM_LIBC_FUNCTION(unsigned, stdc_count_ones_ui, (unsigned value)) {
-  return static_cast<unsigned>(cpp::count_ones(value));
+  return static_cast<unsigned>(cpp::popcount(value));
 }
 
 } // namespace LIBC_NAMESPACE
diff --git a/libc/src/stdbit/stdc_count_ones_ul.cpp b/libc/src/stdbit/stdc_count_ones_ul.cpp
index 83f3279d791937..ed86653fc7ee2e 100644
--- a/libc/src/stdbit/stdc_count_ones_ul.cpp
+++ b/libc/src/stdbit/stdc_count_ones_ul.cpp
@@ -14,7 +14,7 @@
 namespace LIBC_NAMESPACE {
 
 LLVM_LIBC_FUNCTION(unsigned, stdc_count_ones_ul, (unsigned long value)) {
-  return static_cast<unsigned>(cpp::count_ones(value));
+  return static_cast<unsigned>(cpp::popcount(value));
 }
 
 } // namespace LIBC_NAMESPACE
diff --git a/libc/src/stdbit/stdc_count_ones_ull.cpp b/libc/src/stdbit/stdc_count_ones_ull.cpp
index 104788aaf21265..c5ecc3cda6477a 100644
--- a/libc/src/stdbit/stdc_count_ones_ull.cpp
+++ b/libc/src/stdbit/stdc_count_ones_ull.cpp
@@ -14,7 +14,7 @@
 namespace LIBC_NAMESPACE {
 
 LLVM_LIBC_FUNCTION(unsigned, stdc_count_ones_ull, (unsigned long long value)) {
-  return static_cast<unsigned>(cpp::count_ones(value));
+  return static_cast<unsigned>(cpp::popcount(value));
 }
 
 } // namespace LIBC_NAMESPACE
diff --git a/libc/src/stdbit/stdc_count_ones_us.cpp b/libc/src/stdbit/stdc_count_ones_us.cpp
index 4b6ff0b94b626a..465c5c374e7c64 100644
--- a/libc/src/stdbit/stdc_count_ones_us.cpp
+++ b/libc/src/stdbit/stdc_count_ones_us.cpp
@@ -14,7 +14,7 @@
 namespace LIBC_NAMESPACE {
 
 LLVM_LIBC_FUNCTION(unsigned, stdc_count_ones_us, (unsigned short value)) {
-  return static_cast<unsigned>(cpp::count_ones(value));
+  return static_cast<unsigned>(cpp::popcount(value));
 }
 
 } // namespace LIBC_NAMESPACE

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[jhuber6]

Is there a reason we don't use __builtin_popcount? Pretty much every compiler supports it as far as I'm aware, or is there some benefit to relying on compiler optimizations for this.

[jhuber6]

https://godbolt.org/z/M4sf9rr8Y seems the compiler can't completely figure it out. I'd recommend libc_has_builitin if we can.

[nickdesaulniers]

Is there a reason we don't use __builtin_popcount?

128b, but we do use that builtin otherwise. See below (lines 284-295).

[jhuber6]

Ah, didn't catch it in the context. Someone could probably implement it on __128 in clang at least.

[nickdesaulniers]

I filed #82058 which resulted in 21d8332.

We can use __has_builtin to use it for newer compilers.

[jhuber6]

Neat, glad people are on top of things.

[jhuber6]

Seems you missed one uses in the tests.

[nickdesaulniers]

Seems you missed one uses in the tests.

Fixed in 36bfffb PTAL