[libc-commits] [libc] [libc][stdbit] implement stdc_first_trailing_one (C23) (PR #81768)

via libc-commits libc-commits at lists.llvm.org
Wed Feb 14 09:35:16 PST 2024


llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libc

Author: Nick Desaulniers (nickdesaulniers)

<details>
<summary>Changes</summary>



---

Patch is 41.40 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/81768.diff


39 Files Affected:

- (modified) libc/config/linux/x86_64/entrypoints.txt (+10) 
- (modified) libc/docs/stdbit.rst (+12-12) 
- (modified) libc/include/llvm-libc-macros/stdbit-macros.h (+44) 
- (modified) libc/spec/stdc.td (+9-2) 
- (modified) libc/src/__support/CPP/bit.h (+12) 
- (modified) libc/src/stdbit/CMakeLists.txt (+2) 
- (added) libc/src/stdbit/stdc_first_trailing_one_uc.cpp (+21) 
- (added) libc/src/stdbit/stdc_first_trailing_one_uc.h (+18) 
- (added) libc/src/stdbit/stdc_first_trailing_one_ui.cpp (+20) 
- (added) libc/src/stdbit/stdc_first_trailing_one_ui.h (+18) 
- (added) libc/src/stdbit/stdc_first_trailing_one_ul.cpp (+21) 
- (added) libc/src/stdbit/stdc_first_trailing_one_ul.h (+18) 
- (added) libc/src/stdbit/stdc_first_trailing_one_ull.cpp (+21) 
- (added) libc/src/stdbit/stdc_first_trailing_one_ull.h (+18) 
- (added) libc/src/stdbit/stdc_first_trailing_one_us.cpp (+21) 
- (added) libc/src/stdbit/stdc_first_trailing_one_us.h (+18) 
- (added) libc/src/stdbit/stdc_first_trailing_zero_uc.cpp (+21) 
- (added) libc/src/stdbit/stdc_first_trailing_zero_uc.h (+18) 
- (added) libc/src/stdbit/stdc_first_trailing_zero_ui.cpp (+20) 
- (added) libc/src/stdbit/stdc_first_trailing_zero_ui.h (+18) 
- (added) libc/src/stdbit/stdc_first_trailing_zero_ul.cpp (+21) 
- (added) libc/src/stdbit/stdc_first_trailing_zero_ul.h (+18) 
- (added) libc/src/stdbit/stdc_first_trailing_zero_ull.cpp (+21) 
- (added) libc/src/stdbit/stdc_first_trailing_zero_ull.h (+18) 
- (added) libc/src/stdbit/stdc_first_trailing_zero_us.cpp (+21) 
- (added) libc/src/stdbit/stdc_first_trailing_zero_us.h (+18) 
- (modified) libc/test/include/stdbit_test.cpp (+30) 
- (modified) libc/test/src/__support/CPP/bit_test.cpp (+12) 
- (modified) libc/test/src/stdbit/CMakeLists.txt (+2) 
- (added) libc/test/src/stdbit/stdc_first_trailing_one_uc_test.cpp (+20) 
- (added) libc/test/src/stdbit/stdc_first_trailing_one_ui_test.cpp (+20) 
- (added) libc/test/src/stdbit/stdc_first_trailing_one_ul_test.cpp (+20) 
- (added) libc/test/src/stdbit/stdc_first_trailing_one_ull_test.cpp (+20) 
- (added) libc/test/src/stdbit/stdc_first_trailing_one_us_test.cpp (+20) 
- (added) libc/test/src/stdbit/stdc_first_trailing_zero_uc_test.cpp (+20) 
- (added) libc/test/src/stdbit/stdc_first_trailing_zero_ui_test.cpp (+20) 
- (added) libc/test/src/stdbit/stdc_first_trailing_zero_ul_test.cpp (+20) 
- (added) libc/test/src/stdbit/stdc_first_trailing_zero_ull_test.cpp (+21) 
- (added) libc/test/src/stdbit/stdc_first_trailing_zero_us_test.cpp (+20) 


``````````diff
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index fc30bcf56665c7..57b4a1e0f93d4f 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -122,6 +122,16 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.stdbit.stdc_first_leading_one_ui
     libc.src.stdbit.stdc_first_leading_one_ul
     libc.src.stdbit.stdc_first_leading_one_ull
+    libc.src.stdbit.stdc_first_trailing_zero_uc
+    libc.src.stdbit.stdc_first_trailing_zero_us
+    libc.src.stdbit.stdc_first_trailing_zero_ui
+    libc.src.stdbit.stdc_first_trailing_zero_ul
+    libc.src.stdbit.stdc_first_trailing_zero_ull
+    libc.src.stdbit.stdc_first_trailing_one_uc
+    libc.src.stdbit.stdc_first_trailing_one_us
+    libc.src.stdbit.stdc_first_trailing_one_ui
+    libc.src.stdbit.stdc_first_trailing_one_ul
+    libc.src.stdbit.stdc_first_trailing_one_ull
 
     # stdlib.h entrypoints
     libc.src.stdlib.abs
diff --git a/libc/docs/stdbit.rst b/libc/docs/stdbit.rst
index 5ff36dcb0f5929..3bd83ff70c8924 100644
--- a/libc/docs/stdbit.rst
+++ b/libc/docs/stdbit.rst
@@ -61,16 +61,16 @@ stdc_first_leading_one_us    |check|
 stdc_first_leading_one_ui    |check|
 stdc_first_leading_one_ul    |check|
 stdc_first_leading_one_ull   |check|
-stdc_first_trailing_zero_uc
-stdc_first_trailing_zero_us
-stdc_first_trailing_zero_ui
-stdc_first_trailing_zero_ul
-stdc_first_trailing_zero_ull
-stdc_first_trailing_one_uc
-stdc_first_trailing_one_us
-stdc_first_trailing_one_ui
-stdc_first_trailing_one_ul
-stdc_first_trailing_one_ull
+stdc_first_trailing_zero_uc  |check|
+stdc_first_trailing_zero_us  |check|
+stdc_first_trailing_zero_ui  |check|
+stdc_first_trailing_zero_ul  |check|
+stdc_first_trailing_zero_ull |check|
+stdc_first_trailing_one_uc   |check|
+stdc_first_trailing_one_us   |check|
+stdc_first_trailing_one_ui   |check|
+stdc_first_trailing_one_ul   |check|
+stdc_first_trailing_one_ull  |check|
 stdc_count_zeros_uc
 stdc_count_zeros_us
 stdc_count_zeros_ui
@@ -120,8 +120,8 @@ stdc_trailing_zeros        |check|
 stdc_trailing_ones         |check|
 stdc_first_leading_zero    |check|
 stdc_first_leading_one     |check|
-stdc_first_trailing_zero
-stdc_first_trailing_one
+stdc_first_trailing_zero   |check|
+stdc_first_trailing_one    |check|
 stdc_count_zeros
 stdc_count_ones
 stdc_has_single_bit
diff --git a/libc/include/llvm-libc-macros/stdbit-macros.h b/libc/include/llvm-libc-macros/stdbit-macros.h
index 87c590e61e3999..0c97da96ebba29 100644
--- a/libc/include/llvm-libc-macros/stdbit-macros.h
+++ b/libc/include/llvm-libc-macros/stdbit-macros.h
@@ -101,6 +101,36 @@ inline unsigned stdc_first_leading_one(unsigned long x) {
 inline unsigned stdc_first_leading_one(unsigned long long x) {
   return stdc_first_leading_one_ull(x);
 }
+inline unsigned stdc_first_trailing_zero(unsigned char x) {
+  return stdc_first_trailing_zero_uc(x);
+}
+inline unsigned stdc_first_trailing_zero(unsigned short x) {
+  return stdc_first_trailing_zero_us(x);
+}
+inline unsigned stdc_first_trailing_zero(unsigned x) {
+  return stdc_first_trailing_zero_ui(x);
+}
+inline unsigned stdc_first_trailing_zero(unsigned long x) {
+  return stdc_first_trailing_zero_ul(x);
+}
+inline unsigned stdc_first_trailing_zero(unsigned long long x) {
+  return stdc_first_trailing_zero_ull(x);
+}
+inline unsigned stdc_first_trailing_one(unsigned char x) {
+  return stdc_first_trailing_one_uc(x);
+}
+inline unsigned stdc_first_trailing_one(unsigned short x) {
+  return stdc_first_trailing_one_us(x);
+}
+inline unsigned stdc_first_trailing_one(unsigned x) {
+  return stdc_first_trailing_one_ui(x);
+}
+inline unsigned stdc_first_trailing_one(unsigned long x) {
+  return stdc_first_trailing_one_ul(x);
+}
+inline unsigned stdc_first_trailing_one(unsigned long long x) {
+  return stdc_first_trailing_one_ull(x);
+}
 #else
 #define stdc_leading_zeros(x)                                                  \
   _Generic((x),                                                                \
@@ -144,6 +174,20 @@ inline unsigned stdc_first_leading_one(unsigned long long x) {
       unsigned: stdc_first_leading_one_ui,                                     \
       unsigned long: stdc_first_leading_one_ul,                                \
       unsigned long long: stdc_first_leading_one_ull)(x)
+#define stdc_first_trailing_zero(x)                                            \
+  _Generic((x),                                                                \
+      unsigned char: stdc_first_trailing_zero_uc,                              \
+      unsigned short: stdc_first_trailing_zero_us,                             \
+      unsigned: stdc_first_trailing_zero_ui,                                   \
+      unsigned long: stdc_first_trailing_zero_ul,                              \
+      unsigned long long: stdc_first_trailing_zero_ull)(x)
+#define stdc_first_trailing_one(x)                                             \
+  _Generic((x),                                                                \
+      unsigned char: stdc_first_trailing_one_uc,                               \
+      unsigned short: stdc_first_trailing_one_us,                              \
+      unsigned: stdc_first_trailing_one_ui,                                    \
+      unsigned long: stdc_first_trailing_one_ul,                               \
+      unsigned long long: stdc_first_trailing_one_ull)(x)
 #endif // __cplusplus
 
 #endif // __LLVM_LIBC_MACROS_STDBIT_MACROS_H
diff --git a/libc/spec/stdc.td b/libc/spec/stdc.td
index 5e87831b907fb5..9ed94638f522ca 100644
--- a/libc/spec/stdc.td
+++ b/libc/spec/stdc.td
@@ -782,7 +782,9 @@ def StdC : StandardSpec<"stdc"> {
         Macro<"stdc_trailing_zeros">,
         Macro<"stdc_trailing_ones">,
         Macro<"stdc_first_leading_zero">,
-        Macro<"stdc_first_leading_one">
+        Macro<"stdc_first_leading_one">,
+        Macro<"stdc_first_trailing_zero">,
+        Macro<"stdc_first_trailing_one">
       ], // Macros
       [], // Types
       [], // Enumerations
@@ -816,7 +818,12 @@ def StdC : StandardSpec<"stdc"> {
           FunctionSpec<"stdc_first_leading_one_us", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedShortType>]>,
           FunctionSpec<"stdc_first_leading_one_ui", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedIntType>]>,
           FunctionSpec<"stdc_first_leading_one_ul", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedLongType>]>,
-          FunctionSpec<"stdc_first_leading_one_ull", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedLongLongType>]>
+          FunctionSpec<"stdc_first_leading_one_ull", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedLongLongType>]>,
+          FunctionSpec<"stdc_first_trailing_one_uc", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedCharType>]>,
+          FunctionSpec<"stdc_first_trailing_one_us", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedShortType>]>,
+          FunctionSpec<"stdc_first_trailing_one_ui", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedIntType>]>,
+          FunctionSpec<"stdc_first_trailing_one_ul", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedLongType>]>,
+          FunctionSpec<"stdc_first_trailing_one_ull", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedLongLongType>]>
       ] // Functions
   >;
 
diff --git a/libc/src/__support/CPP/bit.h b/libc/src/__support/CPP/bit.h
index 23e305ab86219e..f5e50262371f26 100644
--- a/libc/src/__support/CPP/bit.h
+++ b/libc/src/__support/CPP/bit.h
@@ -236,6 +236,18 @@ template <typename T, typename = cpp::enable_if_t<cpp::is_unsigned_v<T>>>
   return first_leading_zero(static_cast<T>(~value));
 }
 
+template <typename T, typename = cpp::enable_if_t<cpp::is_unsigned_v<T>>>
+[[nodiscard]] LIBC_INLINE constexpr int first_trailing_zero(T value) {
+  return value == cpp::numeric_limits<T>::max()
+             ? 0
+             : countr_zero(static_cast<T>(~value)) + 1;
+}
+
+template <typename T, typename = cpp::enable_if_t<cpp::is_unsigned_v<T>>>
+[[nodiscard]] LIBC_INLINE constexpr int first_trailing_one(T value) {
+  return value == cpp::numeric_limits<T>::max() ? 0 : countr_zero(value) + 1;
+}
+
 } // namespace LIBC_NAMESPACE::cpp
 
 #endif // LLVM_LIBC_SRC___SUPPORT_CPP_BIT_H
diff --git a/libc/src/stdbit/CMakeLists.txt b/libc/src/stdbit/CMakeLists.txt
index 6ee93861b8db40..14cc26e206e0d3 100644
--- a/libc/src/stdbit/CMakeLists.txt
+++ b/libc/src/stdbit/CMakeLists.txt
@@ -5,6 +5,8 @@ set(prefixes
   trailing_ones
   first_leading_zero
   first_leading_one
+  first_trailing_zero
+  first_trailing_one
 )
 set(suffixes c s i l ll)
 foreach(prefix IN LISTS prefixes)
diff --git a/libc/src/stdbit/stdc_first_trailing_one_uc.cpp b/libc/src/stdbit/stdc_first_trailing_one_uc.cpp
new file mode 100644
index 00000000000000..6ed35966be61a0
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_trailing_one_uc.cpp
@@ -0,0 +1,21 @@
+//===-- Implementation of stdc_first_trailing_one_uc ----------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdbit/stdc_first_trailing_one_uc.h"
+
+#include "src/__support/CPP/bit.h"
+#include "src/__support/common.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(unsigned, stdc_first_trailing_one_uc,
+                   (unsigned char value)) {
+  return static_cast<unsigned>(cpp::first_trailing_one(value));
+}
+
+} // namespace LIBC_NAMESPACE
diff --git a/libc/src/stdbit/stdc_first_trailing_one_uc.h b/libc/src/stdbit/stdc_first_trailing_one_uc.h
new file mode 100644
index 00000000000000..d733ce850de0fb
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_trailing_one_uc.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for stdc_first_trailing_one_uc ---*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDBIT_STDC_FIRST_TRAILING_ONE_UC_H
+#define LLVM_LIBC_SRC_STDBIT_STDC_FIRST_TRAILING_ONE_UC_H
+
+namespace LIBC_NAMESPACE {
+
+unsigned stdc_first_trailing_one_uc(unsigned char value);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDBIT_STDC_FIRST_TRAILING_ONE_UC_H
diff --git a/libc/src/stdbit/stdc_first_trailing_one_ui.cpp b/libc/src/stdbit/stdc_first_trailing_one_ui.cpp
new file mode 100644
index 00000000000000..a89083bd49507a
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_trailing_one_ui.cpp
@@ -0,0 +1,20 @@
+//===-- Implementation of stdc_first_trailing_one_ui ----------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdbit/stdc_first_trailing_one_ui.h"
+
+#include "src/__support/CPP/bit.h"
+#include "src/__support/common.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(unsigned, stdc_first_trailing_one_ui, (unsigned value)) {
+  return static_cast<unsigned>(cpp::first_trailing_one(value));
+}
+
+} // namespace LIBC_NAMESPACE
diff --git a/libc/src/stdbit/stdc_first_trailing_one_ui.h b/libc/src/stdbit/stdc_first_trailing_one_ui.h
new file mode 100644
index 00000000000000..6a6a5046709aec
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_trailing_one_ui.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for stdc_first_trailing_one_ui ---*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDBIT_STDC_FIRST_TRAILING_ONE_UI_H
+#define LLVM_LIBC_SRC_STDBIT_STDC_FIRST_TRAILING_ONE_UI_H
+
+namespace LIBC_NAMESPACE {
+
+unsigned stdc_first_trailing_one_ui(unsigned value);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDBIT_STDC_FIRST_TRAILING_ONE_UI_H
diff --git a/libc/src/stdbit/stdc_first_trailing_one_ul.cpp b/libc/src/stdbit/stdc_first_trailing_one_ul.cpp
new file mode 100644
index 00000000000000..f30078d0f5ffaa
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_trailing_one_ul.cpp
@@ -0,0 +1,21 @@
+//===-- Implementation of stdc_first_trailing_one_ul ----------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdbit/stdc_first_trailing_one_ul.h"
+
+#include "src/__support/CPP/bit.h"
+#include "src/__support/common.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(unsigned, stdc_first_trailing_one_ul,
+                   (unsigned long value)) {
+  return static_cast<unsigned>(cpp::first_trailing_one(value));
+}
+
+} // namespace LIBC_NAMESPACE
diff --git a/libc/src/stdbit/stdc_first_trailing_one_ul.h b/libc/src/stdbit/stdc_first_trailing_one_ul.h
new file mode 100644
index 00000000000000..09b6a9bbbe34a1
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_trailing_one_ul.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for stdc_first_trailing_one_ul ---*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDBIT_STDC_FIRST_TRAILING_ONE_UL_H
+#define LLVM_LIBC_SRC_STDBIT_STDC_FIRST_TRAILING_ONE_UL_H
+
+namespace LIBC_NAMESPACE {
+
+unsigned stdc_first_trailing_one_ul(unsigned long value);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDBIT_STDC_FIRST_TRAILING_ONE_UL_H
diff --git a/libc/src/stdbit/stdc_first_trailing_one_ull.cpp b/libc/src/stdbit/stdc_first_trailing_one_ull.cpp
new file mode 100644
index 00000000000000..2e526a890cda9c
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_trailing_one_ull.cpp
@@ -0,0 +1,21 @@
+//===-- Implementation of stdc_first_trailing_one_ull ---------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdbit/stdc_first_trailing_one_ull.h"
+
+#include "src/__support/CPP/bit.h"
+#include "src/__support/common.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(unsigned, stdc_first_trailing_one_ull,
+                   (unsigned long long value)) {
+  return static_cast<unsigned>(cpp::first_trailing_one(value));
+}
+
+} // namespace LIBC_NAMESPACE
diff --git a/libc/src/stdbit/stdc_first_trailing_one_ull.h b/libc/src/stdbit/stdc_first_trailing_one_ull.h
new file mode 100644
index 00000000000000..3e12a1d7456691
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_trailing_one_ull.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for stdc_first_trailing_one_ull --*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDBIT_STDC_FIRST_TRAILING_ONE_ULL_H
+#define LLVM_LIBC_SRC_STDBIT_STDC_FIRST_TRAILING_ONE_ULL_H
+
+namespace LIBC_NAMESPACE {
+
+unsigned stdc_first_trailing_one_ull(unsigned long long value);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDBIT_STDC_FIRST_TRAILING_ONE_ULL_H
diff --git a/libc/src/stdbit/stdc_first_trailing_one_us.cpp b/libc/src/stdbit/stdc_first_trailing_one_us.cpp
new file mode 100644
index 00000000000000..e4c88e0d7906b9
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_trailing_one_us.cpp
@@ -0,0 +1,21 @@
+//===-- Implementation of stdc_first_trailing_one_us ----------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdbit/stdc_first_trailing_one_us.h"
+
+#include "src/__support/CPP/bit.h"
+#include "src/__support/common.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(unsigned, stdc_first_trailing_one_us,
+                   (unsigned short value)) {
+  return static_cast<unsigned>(cpp::first_trailing_one(value));
+}
+
+} // namespace LIBC_NAMESPACE
diff --git a/libc/src/stdbit/stdc_first_trailing_one_us.h b/libc/src/stdbit/stdc_first_trailing_one_us.h
new file mode 100644
index 00000000000000..f380898fc68cde
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_trailing_one_us.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for stdc_first_trailing_one_us ---*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDBIT_STDC_FIRST_TRAILING_ONE_US_H
+#define LLVM_LIBC_SRC_STDBIT_STDC_FIRST_TRAILING_ONE_US_H
+
+namespace LIBC_NAMESPACE {
+
+unsigned stdc_first_trailing_one_us(unsigned short value);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDBIT_STDC_FIRST_TRAILING_ONE_US_H
diff --git a/libc/src/stdbit/stdc_first_trailing_zero_uc.cpp b/libc/src/stdbit/stdc_first_trailing_zero_uc.cpp
new file mode 100644
index 00000000000000..5825d5d441c591
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_trailing_zero_uc.cpp
@@ -0,0 +1,21 @@
+//===-- Implementation of stdc_first_trailing_zero_uc ---------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdbit/stdc_first_trailing_zero_uc.h"
+
+#include "src/__support/CPP/bit.h"
+#include "src/__support/common.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(unsigned, stdc_first_trailing_zero_uc,
+                   (unsigned char value)) {
+  return static_cast<unsigned>(cpp::first_trailing_zero(value));
+}
+
+} // namespace LIBC_NAMESPACE
diff --git a/libc/src/stdbit/stdc_first_trailing_zero_uc.h b/libc/src/stdbit/stdc_first_trailing_zero_uc.h
new file mode 100644
index 00000000000000..242472ae34f2e6
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_trailing_zero_uc.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for stdc_first_trailing_zero_uc ---*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDBIT_STDC_FIRST_TRAILING_ZERO_UC_H
+#define LLVM_LIBC_SRC_STDBIT_STDC_FIRST_TRAILING_ZERO_UC_H
+
+namespace LIBC_NAMESPACE {
+
+unsigned stdc_first_trailing_zero_uc(unsigned char value);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDBIT_STDC_FIRST_TRAILING_ZERO_UC_H
diff --git a/libc/src/stdbit/stdc_first_trailing_zero_ui.cpp b/libc/src/stdbit/stdc_first_trailing_zero_ui.cpp
new file mode 100644
index 00000000000000..3b51b5fa22c324
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_trailing_zero_ui.cpp
@@ -0,0 +1,20 @@
+//===-- Implementation of stdc_first_trailing_zero_ui ---------------------===//
+//
+// Part of the LL...
[truncated]

``````````

</details>


https://github.com/llvm/llvm-project/pull/81768


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