Remove non standard bit functions specializations, add documentation about non standard functions in the bit header.

Author: gchatelet

libc/src/__support/CPP/bit.h

@@ -239,18 +239,21 @@ LIBC_INLINE constexpr To bit_or_static_cast(const From &from) {
   }
 }
 
+// TODO: remove from 'bit.h' as it is not a standard function.
 template <typename T>
 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
 first_leading_zero(T value) {
   return value == cpp::numeric_limits<T>::max() ? 0 : countl_one(value) + 1;
 }
 
+// TODO: remove from 'bit.h' as it is not a standard function.
 template <typename T>
 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
 first_leading_one(T value) {
   return first_leading_zero(static_cast<T>(~value));
 }
 
+// TODO: remove from 'bit.h' as it is not a standard function.
 template <typename T>
 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
 first_trailing_zero(T value) {
@@ -259,6 +262,7 @@ first_trailing_zero(T value) {
              : countr_zero(static_cast<T>(~value)) + 1;
 }
 
+// TODO: remove from 'bit.h' as it is not a standard function.
 template <typename T>
 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
 first_trailing_one(T value) {
@@ -268,6 +272,8 @@ first_trailing_one(T value) {
 /// 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) {
@@ -290,6 +296,7 @@ ADD_SPECIALIZATION(unsigned long long, __builtin_popcountll)
 // TODO: 128b specializations?
 #undef ADD_SPECIALIZATION
 
+// TODO: remove from 'bit.h' as it is not a standard function.
 template <typename T>
 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, int>
 count_zeros(T value) {

libc/src/__support/UInt.h

@@ -1050,58 +1050,6 @@ rotr(T value, int rotate) {
   return (value >> rotate) | (value << (N - rotate));
 }
 
-// Specialization of cpp::first_leading_zero ('bit.h') for BigInt.
-template <typename T>
-[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_big_int_v<T>, int>
-first_leading_zero(T value) {
-  return value == cpp::numeric_limits<T>::max() ? 0 : countl_one(value) + 1;
-}
-
-// Specialization of cpp::first_leading_one ('bit.h') for BigInt.
-template <typename T>
-[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_big_int_v<T>, int>
-first_leading_one(T value) {
-  // TODO : Implement a faster version not involving operator~.
-  return first_leading_zero(static_cast<T>(~value));
-}
-
-// Specialization of cpp::first_trailing_zero ('bit.h') for BigInt.
-template <typename T>
-[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_big_int_v<T>, int>
-first_trailing_zero(T value) {
-  // TODO : Implement a faster version not involving operator~.
-  return value == cpp::numeric_limits<T>::max()
-             ? 0
-             : countr_zero(static_cast<T>(~value)) + 1;
-}
-
-// Specialization of cpp::first_trailing_one ('bit.h') for BigInt.
-template <typename T>
-[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_big_int_v<T>, int>
-first_trailing_one(T value) {
-  return value == cpp::numeric_limits<T>::max() ? 0 : countr_zero(value) + 1;
-}
-
-// Specialization of cpp::count_ones ('bit.h') for BigInt.
-template <typename T>
-[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_big_int_v<T>, int>
-count_ones(T value) {
-  int count = 0;
-  for (auto word : value.val)
-    count += count_ones(word);
-  return count;
-}
-
-// Specialization of cpp::count_zeros ('bit.h') for BigInt.
-template <typename T>
-[[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_big_int_v<T>, int>
-count_zeros(T value) {
-  int count = 0;
-  for (auto word : value.val)
-    count += count_zeros(word);
-  return count;
-}
-
 } // namespace LIBC_NAMESPACE::cpp
 
 #endif // LLVM_LIBC_SRC___SUPPORT_UINT_H

libc/test/src/__support/CPP/bit_test.cpp

@@ -16,13 +16,19 @@
 
 namespace LIBC_NAMESPACE::cpp {
 
-using UnsignedTypes =
-    testing::TypeList<unsigned char, unsigned short, unsigned int,
-                      unsigned long, unsigned long long,
+using UnsignedTypesNoBigInt = testing::TypeList<
 #if defined(__SIZEOF_INT128__)
-                      __uint128_t,
+    __uint128_t,
 #endif
-                      cpp::UInt<128>>;
+    unsigned char, unsigned short, unsigned int, unsigned long,
+    unsigned long long>;
+
+using UnsignedTypes = testing::TypeList<
+#if defined(__SIZEOF_INT128__)
+    __uint128_t,
+#endif
+    unsigned char, unsigned short, unsigned int, unsigned long,
+    unsigned long long, cpp::UInt<128>>;
 
 TYPED_TEST(LlvmLibcBitTest, HasSingleBit, UnsignedTypes) {
   constexpr auto ZERO = T(0);
@@ -223,39 +229,39 @@ TEST(LlvmLibcBitTest, Rotr) {
             rotr<uint64_t>(0x12345678deadbeefULL, -19));
 }
 
-TYPED_TEST(LlvmLibcBitTest, FirstLeadingZero, UnsignedTypes) {
+TYPED_TEST(LlvmLibcBitTest, FirstLeadingZero, UnsignedTypesNoBigInt) {
   EXPECT_EQ(first_leading_zero<T>(cpp::numeric_limits<T>::max()), 0);
   for (int i = 0U; i != cpp::numeric_limits<T>::digits; ++i)
     EXPECT_EQ(first_leading_zero<T>(~(T(1) << i)),
               cpp::numeric_limits<T>::digits - i);
 }
 
-TYPED_TEST(LlvmLibcBitTest, FirstLeadingOne, UnsignedTypes) {
+TYPED_TEST(LlvmLibcBitTest, FirstLeadingOne, UnsignedTypesNoBigInt) {
   EXPECT_EQ(first_leading_one<T>(static_cast<T>(0)), 0);
   for (int i = 0U; i != cpp::numeric_limits<T>::digits; ++i)
     EXPECT_EQ(first_leading_one<T>(T(1) << i),
               cpp::numeric_limits<T>::digits - i);
 }
 
-TYPED_TEST(LlvmLibcBitTest, FirstTrailingZero, UnsignedTypes) {
+TYPED_TEST(LlvmLibcBitTest, FirstTrailingZero, UnsignedTypesNoBigInt) {
   EXPECT_EQ(first_trailing_zero<T>(cpp::numeric_limits<T>::max()), 0);
   for (int i = 0U; i != cpp::numeric_limits<T>::digits; ++i)
     EXPECT_EQ(first_trailing_zero<T>(~(T(1) << i)), i + 1);
 }
 
-TYPED_TEST(LlvmLibcBitTest, FirstTrailingOne, UnsignedTypes) {
+TYPED_TEST(LlvmLibcBitTest, FirstTrailingOne, UnsignedTypesNoBigInt) {
   EXPECT_EQ(first_trailing_one<T>(cpp::numeric_limits<T>::max()), 0);
   for (int i = 0U; i != cpp::numeric_limits<T>::digits; ++i)
     EXPECT_EQ(first_trailing_one<T>(T(1) << i), i + 1);
 }
 
-TYPED_TEST(LlvmLibcBitTest, CountZeros, UnsignedTypes) {
+TYPED_TEST(LlvmLibcBitTest, CountZeros, UnsignedTypesNoBigInt) {
   EXPECT_EQ(count_zeros(T(0)), cpp::numeric_limits<T>::digits);
   for (int i = 0; i != cpp::numeric_limits<T>::digits; ++i)
     EXPECT_EQ(count_zeros<T>(cpp::numeric_limits<T>::max() >> i), i);
 }
 
-TYPED_TEST(LlvmLibcBitTest, CountOnes, UnsignedTypes) {
+TYPED_TEST(LlvmLibcBitTest, CountOnes, UnsignedTypesNoBigInt) {
   EXPECT_EQ(count_ones(T(0)), 0);
   for (int i = 0; i != cpp::numeric_limits<T>::digits; ++i)
     EXPECT_EQ(count_ones<T>(cpp::numeric_limits<T>::max() >> i),