[libc-commits] [libc] [libc][stdbit] implement stdc_first_leading_zero (C23) (PR #81340)
Nick Desaulniers via libc-commits
libc-commits at lists.llvm.org
Fri Feb 9 16:04:46 PST 2024
https://github.com/nickdesaulniers updated https://github.com/llvm/llvm-project/pull/81340
>From f8b9b93e254a4a3d66c0a6f6bd66bad77e36b88e Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers at google.com>
Date: Fri, 9 Feb 2024 15:10:49 -0800
Subject: [PATCH 1/2] [libc][stdbit] implement stdc_first_leading_zero (C23)
---
libc/config/linux/x86_64/entrypoints.txt | 5 +++++
libc/include/llvm-libc-macros/stdbit-macros.h | 22 +++++++++++++++++++
libc/spec/stdc.td | 10 +++++++--
libc/src/__support/CPP/bit.h | 7 ++++++
libc/src/stdbit/CMakeLists.txt | 1 +
.../src/stdbit/stdc_first_leading_zero_uc.cpp | 21 ++++++++++++++++++
libc/src/stdbit/stdc_first_leading_zero_uc.h | 18 +++++++++++++++
.../src/stdbit/stdc_first_leading_zero_ui.cpp | 20 +++++++++++++++++
libc/src/stdbit/stdc_first_leading_zero_ui.h | 18 +++++++++++++++
.../src/stdbit/stdc_first_leading_zero_ul.cpp | 21 ++++++++++++++++++
libc/src/stdbit/stdc_first_leading_zero_ul.h | 18 +++++++++++++++
.../stdbit/stdc_first_leading_zero_ull.cpp | 21 ++++++++++++++++++
libc/src/stdbit/stdc_first_leading_zero_ull.h | 18 +++++++++++++++
.../src/stdbit/stdc_first_leading_zero_us.cpp | 21 ++++++++++++++++++
libc/src/stdbit/stdc_first_leading_zero_us.h | 18 +++++++++++++++
libc/test/include/stdbit_test.cpp | 15 +++++++++++++
libc/test/src/__support/CPP/bit_test.cpp | 7 ++++++
libc/test/src/stdbit/CMakeLists.txt | 1 +
.../stdc_first_leading_zero_uc_test.cpp | 21 ++++++++++++++++++
.../stdc_first_leading_zero_ui_test.cpp | 21 ++++++++++++++++++
.../stdc_first_leading_zero_ul_test.cpp | 21 ++++++++++++++++++
.../stdc_first_leading_zero_ull_test.cpp | 21 ++++++++++++++++++
.../stdc_first_leading_zero_us_test.cpp | 21 ++++++++++++++++++
23 files changed, 365 insertions(+), 2 deletions(-)
create mode 100644 libc/src/stdbit/stdc_first_leading_zero_uc.cpp
create mode 100644 libc/src/stdbit/stdc_first_leading_zero_uc.h
create mode 100644 libc/src/stdbit/stdc_first_leading_zero_ui.cpp
create mode 100644 libc/src/stdbit/stdc_first_leading_zero_ui.h
create mode 100644 libc/src/stdbit/stdc_first_leading_zero_ul.cpp
create mode 100644 libc/src/stdbit/stdc_first_leading_zero_ul.h
create mode 100644 libc/src/stdbit/stdc_first_leading_zero_ull.cpp
create mode 100644 libc/src/stdbit/stdc_first_leading_zero_ull.h
create mode 100644 libc/src/stdbit/stdc_first_leading_zero_us.cpp
create mode 100644 libc/src/stdbit/stdc_first_leading_zero_us.h
create mode 100644 libc/test/src/stdbit/stdc_first_leading_zero_uc_test.cpp
create mode 100644 libc/test/src/stdbit/stdc_first_leading_zero_ui_test.cpp
create mode 100644 libc/test/src/stdbit/stdc_first_leading_zero_ul_test.cpp
create mode 100644 libc/test/src/stdbit/stdc_first_leading_zero_ull_test.cpp
create mode 100644 libc/test/src/stdbit/stdc_first_leading_zero_us_test.cpp
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 52a3ce0132bdcb..868de0a9e3c19c 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -112,6 +112,11 @@ set(TARGET_LIBC_ENTRYPOINTS
libc.src.stdbit.stdc_trailing_ones_ui
libc.src.stdbit.stdc_trailing_ones_ul
libc.src.stdbit.stdc_trailing_ones_ull
+ libc.src.stdbit.stdc_first_leading_zero_uc
+ libc.src.stdbit.stdc_first_leading_zero_us
+ libc.src.stdbit.stdc_first_leading_zero_ui
+ libc.src.stdbit.stdc_first_leading_zero_ul
+ libc.src.stdbit.stdc_first_leading_zero_ull
# stdlib.h entrypoints
libc.src.stdlib.abs
diff --git a/libc/include/llvm-libc-macros/stdbit-macros.h b/libc/include/llvm-libc-macros/stdbit-macros.h
index c55529e5c0e943..693a45e63419ff 100644
--- a/libc/include/llvm-libc-macros/stdbit-macros.h
+++ b/libc/include/llvm-libc-macros/stdbit-macros.h
@@ -71,6 +71,21 @@ inline unsigned stdc_trailing_ones(unsigned long x) {
inline unsigned stdc_trailing_ones(unsigned long long x) {
return stdc_trailing_ones_ull(x);
}
+inline unsigned stdc_first_leading_zero(unsigned char x) {
+ return stdc_first_leading_zero_uc(x);
+}
+inline unsigned stdc_first_leading_zero(unsigned short x) {
+ return stdc_first_leading_zero_us(x);
+}
+inline unsigned stdc_first_leading_zero(unsigned x) {
+ return stdc_first_leading_zero_ui(x);
+}
+inline unsigned stdc_first_leading_zero(unsigned long x) {
+ return stdc_first_leading_zero_ul(x);
+}
+inline unsigned stdc_first_leading_zero(unsigned long long x) {
+ return stdc_first_leading_zero_ull(x);
+}
#else
#define stdc_leading_zeros(x) \
_Generic((x), \
@@ -100,6 +115,13 @@ inline unsigned stdc_trailing_ones(unsigned long long x) {
unsigned: stdc_trailing_ones_ui, \
unsigned long: stdc_trailing_ones_ul, \
unsigned long long: stdc_trailing_ones_ull)(x)
+#define stdc_first_leading_zero(x) \
+ _Generic((x), \
+ unsigned char: stdc_first_leading_zero_uc, \
+ unsigned short: stdc_first_leading_zero_us, \
+ unsigned: stdc_first_leading_zero_ui, \
+ unsigned long: stdc_first_leading_zero_ul, \
+ unsigned long long: stdc_first_leading_zero_ull)(x)
#endif // __cplusplus
#endif // __LLVM_LIBC_MACROS_STDBIT_MACROS_H
diff --git a/libc/spec/stdc.td b/libc/spec/stdc.td
index 9c8b5e5c466273..983f71628ec4b0 100644
--- a/libc/spec/stdc.td
+++ b/libc/spec/stdc.td
@@ -779,7 +779,8 @@ def StdC : StandardSpec<"stdc"> {
Macro<"stdc_leading_zeros">,
Macro<"stdc_leading_ones">,
Macro<"stdc_trailing_zeros">,
- Macro<"stdc_trailing_ones">
+ Macro<"stdc_trailing_ones">,
+ Macro<"stdc_first_leading_zero">
], // Macros
[], // Types
[], // Enumerations
@@ -803,7 +804,12 @@ def StdC : StandardSpec<"stdc"> {
FunctionSpec<"stdc_trailing_ones_us", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedShortType>]>,
FunctionSpec<"stdc_trailing_ones_ui", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedIntType>]>,
FunctionSpec<"stdc_trailing_ones_ul", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedLongType>]>,
- FunctionSpec<"stdc_trailing_ones_ull", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedLongLongType>]>
+ FunctionSpec<"stdc_trailing_ones_ull", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedLongLongType>]>,
+ FunctionSpec<"stdc_first_leading_zero_uc", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedCharType>]>,
+ FunctionSpec<"stdc_first_leading_zero_us", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedShortType>]>,
+ FunctionSpec<"stdc_first_leading_zero_ui", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedIntType>]>,
+ FunctionSpec<"stdc_first_leading_zero_ul", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedLongType>]>,
+ FunctionSpec<"stdc_first_leading_zero_ull", RetValSpec<UnsignedIntType>, [ArgSpec<UnsignedLongLongType>]>
] // Functions
>;
diff --git a/libc/src/__support/CPP/bit.h b/libc/src/__support/CPP/bit.h
index 122f6b8c332810..0657d1084eb58f 100644
--- a/libc/src/__support/CPP/bit.h
+++ b/libc/src/__support/CPP/bit.h
@@ -238,6 +238,13 @@ LIBC_INLINE constexpr To bit_or_static_cast(const From &from) {
}
}
+template <typename T, typename = cpp::enable_if_t<cpp::is_unsigned_v<T>>>
+[[nodiscard]] LIBC_INLINE constexpr int first_leading_zero(T value) {
+ return value == cpp::numeric_limits<T>::max()
+ ? 0
+ : countl_zero(static_cast<T>(~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 129621f1392894..65d5f344307475 100644
--- a/libc/src/stdbit/CMakeLists.txt
+++ b/libc/src/stdbit/CMakeLists.txt
@@ -3,6 +3,7 @@ set(prefixes
leading_ones
trailing_zeros
trailing_ones
+ first_leading_zero
)
set(suffixes c s i l ll)
foreach(prefix IN LISTS prefixes)
diff --git a/libc/src/stdbit/stdc_first_leading_zero_uc.cpp b/libc/src/stdbit/stdc_first_leading_zero_uc.cpp
new file mode 100644
index 00000000000000..ffc1d9247406a2
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_leading_zero_uc.cpp
@@ -0,0 +1,21 @@
+//===-- Implementation of stdc_first_leading_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_leading_zero_uc.h"
+
+#include "src/__support/CPP/bit.h"
+#include "src/__support/common.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(unsigned, stdc_first_leading_zero_uc,
+ (unsigned char value)) {
+ return static_cast<unsigned>(cpp::first_leading_zero(value));
+}
+
+} // namespace LIBC_NAMESPACE
diff --git a/libc/src/stdbit/stdc_first_leading_zero_uc.h b/libc/src/stdbit/stdc_first_leading_zero_uc.h
new file mode 100644
index 00000000000000..63ecd20acc6183
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_leading_zero_uc.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for stdc_first_leading_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_LEADING_ZERO_UC_H
+#define LLVM_LIBC_SRC_STDBIT_STDC_FIRST_LEADING_ZERO_UC_H
+
+namespace LIBC_NAMESPACE {
+
+unsigned stdc_first_leading_zero_uc(unsigned char value);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDBIT_STDC_FIRST_LEADING_ZERO_UC_H
diff --git a/libc/src/stdbit/stdc_first_leading_zero_ui.cpp b/libc/src/stdbit/stdc_first_leading_zero_ui.cpp
new file mode 100644
index 00000000000000..1eeab2963e6aa7
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_leading_zero_ui.cpp
@@ -0,0 +1,20 @@
+//===-- Implementation of stdc_first_leading_zero_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_leading_zero_ui.h"
+
+#include "src/__support/CPP/bit.h"
+#include "src/__support/common.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(unsigned, stdc_first_leading_zero_ui, (unsigned value)) {
+ return static_cast<unsigned>(cpp::first_leading_zero(value));
+}
+
+} // namespace LIBC_NAMESPACE
diff --git a/libc/src/stdbit/stdc_first_leading_zero_ui.h b/libc/src/stdbit/stdc_first_leading_zero_ui.h
new file mode 100644
index 00000000000000..d8d5d9345010f3
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_leading_zero_ui.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for stdc_first_leading_zero_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_LEADING_ZERO_UI_H
+#define LLVM_LIBC_SRC_STDBIT_STDC_FIRST_LEADING_ZERO_UI_H
+
+namespace LIBC_NAMESPACE {
+
+unsigned stdc_first_leading_zero_ui(unsigned value);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDBIT_STDC_FIRST_LEADING_ZERO_UI_H
diff --git a/libc/src/stdbit/stdc_first_leading_zero_ul.cpp b/libc/src/stdbit/stdc_first_leading_zero_ul.cpp
new file mode 100644
index 00000000000000..6743d3eda5168c
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_leading_zero_ul.cpp
@@ -0,0 +1,21 @@
+//===-- Implementation of stdc_first_leading_zero_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_leading_zero_ul.h"
+
+#include "src/__support/CPP/bit.h"
+#include "src/__support/common.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(unsigned, stdc_first_leading_zero_ul,
+ (unsigned long value)) {
+ return static_cast<unsigned>(cpp::first_leading_zero(value));
+}
+
+} // namespace LIBC_NAMESPACE
diff --git a/libc/src/stdbit/stdc_first_leading_zero_ul.h b/libc/src/stdbit/stdc_first_leading_zero_ul.h
new file mode 100644
index 00000000000000..8df1b55c2c3aa8
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_leading_zero_ul.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for stdc_first_leading_zero_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_LEADING_ZERO_UL_H
+#define LLVM_LIBC_SRC_STDBIT_STDC_FIRST_LEADING_ZERO_UL_H
+
+namespace LIBC_NAMESPACE {
+
+unsigned stdc_first_leading_zero_ul(unsigned long value);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDBIT_STDC_FIRST_LEADING_ZERO_UL_H
diff --git a/libc/src/stdbit/stdc_first_leading_zero_ull.cpp b/libc/src/stdbit/stdc_first_leading_zero_ull.cpp
new file mode 100644
index 00000000000000..8128dd3d59a7bf
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_leading_zero_ull.cpp
@@ -0,0 +1,21 @@
+//===-- Implementation of stdc_first_leading_zero_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_leading_zero_ull.h"
+
+#include "src/__support/CPP/bit.h"
+#include "src/__support/common.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(unsigned, stdc_first_leading_zero_ull,
+ (unsigned long long value)) {
+ return static_cast<unsigned>(cpp::first_leading_zero(value));
+}
+
+} // namespace LIBC_NAMESPACE
diff --git a/libc/src/stdbit/stdc_first_leading_zero_ull.h b/libc/src/stdbit/stdc_first_leading_zero_ull.h
new file mode 100644
index 00000000000000..9aec5e7e554531
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_leading_zero_ull.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for stdc_first_leading_zero_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_LEADING_ZERO_ULL_H
+#define LLVM_LIBC_SRC_STDBIT_STDC_FIRST_LEADING_ZERO_ULL_H
+
+namespace LIBC_NAMESPACE {
+
+unsigned stdc_first_leading_zero_ull(unsigned long long value);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDBIT_STDC_FIRST_LEADING_ZERO_ULL_H
diff --git a/libc/src/stdbit/stdc_first_leading_zero_us.cpp b/libc/src/stdbit/stdc_first_leading_zero_us.cpp
new file mode 100644
index 00000000000000..d931535e7690a6
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_leading_zero_us.cpp
@@ -0,0 +1,21 @@
+//===-- Implementation of stdc_first_leading_zero_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_leading_zero_us.h"
+
+#include "src/__support/CPP/bit.h"
+#include "src/__support/common.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(unsigned, stdc_first_leading_zero_us,
+ (unsigned short value)) {
+ return static_cast<unsigned>(cpp::first_leading_zero(value));
+}
+
+} // namespace LIBC_NAMESPACE
diff --git a/libc/src/stdbit/stdc_first_leading_zero_us.h b/libc/src/stdbit/stdc_first_leading_zero_us.h
new file mode 100644
index 00000000000000..8587378069ce1a
--- /dev/null
+++ b/libc/src/stdbit/stdc_first_leading_zero_us.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for stdc_first_leading_zero_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_LEADING_ZERO_US_H
+#define LLVM_LIBC_SRC_STDBIT_STDC_FIRST_LEADING_ZERO_US_H
+
+namespace LIBC_NAMESPACE {
+
+unsigned stdc_first_leading_zero_us(unsigned short value);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDBIT_STDC_FIRST_LEADING_ZERO_US_H
diff --git a/libc/test/include/stdbit_test.cpp b/libc/test/include/stdbit_test.cpp
index 8d5d4c162938ec..9a66a76de20bc5 100644
--- a/libc/test/include/stdbit_test.cpp
+++ b/libc/test/include/stdbit_test.cpp
@@ -43,6 +43,13 @@ unsigned stdc_trailing_ones_us(unsigned short) noexcept { return 0xDBU; }
unsigned stdc_trailing_ones_ui(unsigned) noexcept { return 0xDCU; }
unsigned stdc_trailing_ones_ul(unsigned long) noexcept { return 0xDDU; }
unsigned stdc_trailing_ones_ull(unsigned long long) noexcept { return 0xDFU; }
+unsigned stdc_first_leading_zero_uc(unsigned char) noexcept { return 0xEAU; }
+unsigned stdc_first_leading_zero_us(unsigned short) noexcept { return 0xEBU; }
+unsigned stdc_first_leading_zero_ui(unsigned) noexcept { return 0xECU; }
+unsigned stdc_first_leading_zero_ul(unsigned long) noexcept { return 0xEDU; }
+unsigned stdc_first_leading_zero_ull(unsigned long long) noexcept {
+ return 0xEFU;
+}
}
#include "include/llvm-libc-macros/stdbit-macros.h"
@@ -78,3 +85,11 @@ TEST(LlvmLibcStdbitTest, TypeGenericMacroTrailingOnes) {
EXPECT_EQ(stdc_trailing_ones(0UL), 0xDDU);
EXPECT_EQ(stdc_trailing_ones(0ULL), 0xDFU);
}
+
+TEST(LlvmLibcStdbitTest, TypeGenericMacroFirstLeadingZero) {
+ EXPECT_EQ(stdc_first_leading_zero(static_cast<unsigned char>(0U)), 0xEAU);
+ EXPECT_EQ(stdc_first_leading_zero(static_cast<unsigned short>(0U)), 0xEBU);
+ EXPECT_EQ(stdc_first_leading_zero(0U), 0xECU);
+ EXPECT_EQ(stdc_first_leading_zero(0UL), 0xEDU);
+ EXPECT_EQ(stdc_first_leading_zero(0ULL), 0xEFU);
+}
diff --git a/libc/test/src/__support/CPP/bit_test.cpp b/libc/test/src/__support/CPP/bit_test.cpp
index fef551bc1f0e2d..00d8ca5d293ace 100644
--- a/libc/test/src/__support/CPP/bit_test.cpp
+++ b/libc/test/src/__support/CPP/bit_test.cpp
@@ -206,4 +206,11 @@ TEST(LlvmLibcBitTest, Rotr) {
rotr<uint64_t>(0x12345678deadbeefULL, -19));
}
+TYPED_TEST(LlvmLibcBitTest, FirstLeadingZero, UnsignedTypes) {
+ 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);
+}
+
} // namespace LIBC_NAMESPACE::cpp
diff --git a/libc/test/src/stdbit/CMakeLists.txt b/libc/test/src/stdbit/CMakeLists.txt
index fab5f67bbd9be4..bc7e49d186a0d5 100644
--- a/libc/test/src/stdbit/CMakeLists.txt
+++ b/libc/test/src/stdbit/CMakeLists.txt
@@ -5,6 +5,7 @@ set(prefixes
leading_ones
trailing_zeros
trailing_ones
+ first_leading_zero
)
set(suffixes c s i l ll)
foreach(prefix IN LISTS prefixes)
diff --git a/libc/test/src/stdbit/stdc_first_leading_zero_uc_test.cpp b/libc/test/src/stdbit/stdc_first_leading_zero_uc_test.cpp
new file mode 100644
index 00000000000000..ac7e8c7d9e64be
--- /dev/null
+++ b/libc/test/src/stdbit/stdc_first_leading_zero_uc_test.cpp
@@ -0,0 +1,21 @@
+//===-- Unittests for stdc_first_leading_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/__support/CPP/limits.h"
+#include "src/stdbit/stdc_first_leading_zero_uc.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcStdcFirstLeadingZeroUcTest, ALL) {
+ EXPECT_EQ(LIBC_NAMESPACE::stdc_first_leading_zero_uc(UCHAR_MAX), 0U);
+}
+
+TEST(LlvmLibcStdcFirstLeadingZeroUcTest, ZeroHot) {
+ for (unsigned i = 0U; i != UCHAR_WIDTH; ++i)
+ EXPECT_EQ(LIBC_NAMESPACE::stdc_first_leading_zero_uc(~(1U << i)),
+ UCHAR_WIDTH - i);
+}
diff --git a/libc/test/src/stdbit/stdc_first_leading_zero_ui_test.cpp b/libc/test/src/stdbit/stdc_first_leading_zero_ui_test.cpp
new file mode 100644
index 00000000000000..79a4e539434949
--- /dev/null
+++ b/libc/test/src/stdbit/stdc_first_leading_zero_ui_test.cpp
@@ -0,0 +1,21 @@
+//===-- Unittests for stdc_first_leading_zero_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/__support/CPP/limits.h"
+#include "src/stdbit/stdc_first_leading_zero_ui.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcStdcFirstLeadingZeroUiTest, ALL) {
+ EXPECT_EQ(LIBC_NAMESPACE::stdc_first_leading_zero_ui(UINT_MAX), 0U);
+}
+
+TEST(LlvmLibcStdcFirstLeadingZeroUiTest, ZeroHot) {
+ for (unsigned i = 0U; i != UINT_WIDTH; ++i)
+ EXPECT_EQ(LIBC_NAMESPACE::stdc_first_leading_zero_ui(~(1U << i)),
+ UINT_WIDTH - i);
+}
diff --git a/libc/test/src/stdbit/stdc_first_leading_zero_ul_test.cpp b/libc/test/src/stdbit/stdc_first_leading_zero_ul_test.cpp
new file mode 100644
index 00000000000000..92cac6c8bffdb9
--- /dev/null
+++ b/libc/test/src/stdbit/stdc_first_leading_zero_ul_test.cpp
@@ -0,0 +1,21 @@
+//===-- Unittests for stdc_first_leading_zero_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/__support/CPP/limits.h"
+#include "src/stdbit/stdc_first_leading_zero_ul.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcStdcFirstLeadingZeroUlTest, ALL) {
+ EXPECT_EQ(LIBC_NAMESPACE::stdc_first_leading_zero_ul(ULONG_MAX), 0U);
+}
+
+TEST(LlvmLibcStdcFirstLeadingZeroUlTest, ZeroHot) {
+ for (unsigned i = 0U; i != ULONG_WIDTH; ++i)
+ EXPECT_EQ(LIBC_NAMESPACE::stdc_first_leading_zero_ul(~(1UL << i)),
+ ULONG_WIDTH - i);
+}
diff --git a/libc/test/src/stdbit/stdc_first_leading_zero_ull_test.cpp b/libc/test/src/stdbit/stdc_first_leading_zero_ull_test.cpp
new file mode 100644
index 00000000000000..a5afdad591aed2
--- /dev/null
+++ b/libc/test/src/stdbit/stdc_first_leading_zero_ull_test.cpp
@@ -0,0 +1,21 @@
+//===-- Unittests for stdc_first_leading_zero_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/__support/CPP/limits.h"
+#include "src/stdbit/stdc_first_leading_zero_ull.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcStdcFirstLeadingZeroUllTest, ALL) {
+ EXPECT_EQ(LIBC_NAMESPACE::stdc_first_leading_zero_ull(ULLONG_MAX), 0U);
+}
+
+TEST(LlvmLibcStdcFirstLeadingZeroUllTest, ZeroHot) {
+ for (unsigned i = 0U; i != ULLONG_WIDTH; ++i)
+ EXPECT_EQ(LIBC_NAMESPACE::stdc_first_leading_zero_ull(~(1ULL << i)),
+ ULLONG_WIDTH - i);
+}
diff --git a/libc/test/src/stdbit/stdc_first_leading_zero_us_test.cpp b/libc/test/src/stdbit/stdc_first_leading_zero_us_test.cpp
new file mode 100644
index 00000000000000..37f8612675a7a1
--- /dev/null
+++ b/libc/test/src/stdbit/stdc_first_leading_zero_us_test.cpp
@@ -0,0 +1,21 @@
+//===-- Unittests for stdc_first_leading_zero_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/__support/CPP/limits.h"
+#include "src/stdbit/stdc_first_leading_zero_us.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcStdcFirstLeadingZeroUsTest, ALL) {
+ EXPECT_EQ(LIBC_NAMESPACE::stdc_first_leading_zero_us(USHRT_MAX), 0U);
+}
+
+TEST(LlvmLibcStdcFirstLeadingZeroUsTest, ZeroHot) {
+ for (unsigned i = 0U; i != USHRT_WIDTH; ++i)
+ EXPECT_EQ(LIBC_NAMESPACE::stdc_first_leading_zero_us(~(1U << i)),
+ USHRT_WIDTH - i);
+}
>From 87518df24b71390ed60bab4c8bce6c08486278a7 Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <ndesaulniers at google.com>
Date: Fri, 9 Feb 2024 16:04:01 -0800
Subject: [PATCH 2/2] add specialization
---
libc/src/__support/CPP/bit.h | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)
diff --git a/libc/src/__support/CPP/bit.h b/libc/src/__support/CPP/bit.h
index 0657d1084eb58f..f6c0eb7720910f 100644
--- a/libc/src/__support/CPP/bit.h
+++ b/libc/src/__support/CPP/bit.h
@@ -238,6 +238,14 @@ LIBC_INLINE constexpr To bit_or_static_cast(const From &from) {
}
}
+#define ADD_SPECIALIZATION(NAME, TYPE, BUILTIN) \
+ template <> [[nodiscard]] LIBC_INLINE constexpr int NAME<TYPE>(TYPE value) { \
+ static_assert(cpp::is_unsigned_v<TYPE>); \
+ return value == cpp::numeric_limits<TYPE>::max() \
+ ? 0 \
+ : BUILTIN(static_cast<TYPE>(~value)) + 1; \
+ }
+
template <typename T, typename = cpp::enable_if_t<cpp::is_unsigned_v<T>>>
[[nodiscard]] LIBC_INLINE constexpr int first_leading_zero(T value) {
return value == cpp::numeric_limits<T>::max()
@@ -245,6 +253,21 @@ template <typename T, typename = cpp::enable_if_t<cpp::is_unsigned_v<T>>>
: countl_zero(static_cast<T>(~value)) + 1;
}
+#if LIBC_HAS_BUILTIN(__builtin_clzs)
+ADD_SPECIALIZATION(first_leading_zero, unsigned short, __builtin_clzs)
+#endif
+#if LIBC_HAS_BUILTIN(__builtin_clz)
+ADD_SPECIALIZATION(first_leading_zero, unsigned int, __builtin_clz)
+#endif
+#if LIBC_HAS_BUILTIN(__builtin_clzl)
+ADD_SPECIALIZATION(first_leading_zero, unsigned long, __builtin_clzl)
+#endif
+#if LIBC_HAS_BUILTIN(__builtin_clzll)
+ADD_SPECIALIZATION(first_leading_zero, unsigned long long, __builtin_clzll)
+#endif
+
+#undef ADD_SPECIALIZATION
+
} // namespace LIBC_NAMESPACE::cpp
#endif // LLVM_LIBC_SRC___SUPPORT_CPP_BIT_H
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