[libc-commits] [libc] [libc] implement `strings/ffs` (PR #129892)

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@@ -0,0 +1,17 @@
+//===-- Implementation of ffs ---------------------------------------------===//
+//
+// 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/strings/ffs.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(int, ffs, (int i)) { return __builtin_ffs(i); }
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c8ef wrote:

https://github.com/llvm/llvm-project/blob/c861c1a046eb8c1e546a8767e0010904a3c8c385/libc/src/__support/CPP/bit.h#L78-L83

I noticed that the `countr_zero` function only accepts unsigned input, while `ffs` requires signed input. Similarly, the built-in `ctz` expects unsigned input, whereas `ffs` needs signed input. Given this, would it be better to directly use the built-in for `ffs`?

https://github.com/llvm/llvm-project/pull/129892