[libc][stdbit] implement stdc_count_ones (C23) (#82444)

1 files changed, 21 insertions, 0 deletions

diff --git a/libc/test/src/stdbit/stdc_count_ones_ui_test.cpp b/libc/test/src/stdbit/stdc_count_ones_ui_test.cpp
new file mode 100644
index 000000000000..198e36658421
--- /dev/null
+++ b/libc/test/src/stdbit/stdc_count_ones_ui_test.cpp
@@ -0,0 +1,21 @@
+//===-- Unittests for stdc_count_ones_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_count_ones_ui.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcStdcCountOnesUiTest, Zero) {
+  EXPECT_EQ(LIBC_NAMESPACE::stdc_count_ones_ui(0), 0U);
+}
+
+TEST(LlvmLibcStdcCountOnesUiTest, Ones) {
+  for (unsigned i = 0U; i != UINT_WIDTH; ++i)
+    EXPECT_EQ(LIBC_NAMESPACE::stdc_count_ones_ui(UINT_MAX >> i),
+              UINT_WIDTH - i);
+}