libc: add support for C23 stdbit.h with bit manipulation macros

- Introduced Kconfig options for stdbit.h, allowing architecture-specific and generic implementations.
- Added new documentation for stdbit.h, detailing its usage and configuration.
- Updated CMake and Makefile to handle the inclusion of stdbit.h based on configuration settings.

This enhances the NuttX library with optional C23 bit manipulation utilities, improving functionality for architectures that support it.

Signed-off-by: Arjav Patel <arjav1528@gmail.com>

Documentation/components/libs/libc/index.rst

@@ -51,6 +51,7 @@ functions.  So we have::
   sched     - sched.h
   search    - search.h
   semaphore - semaphore.h
+  stdbit    - stdbit.h (optional C23)
   stdio     - stdio.h
   stdlib    - stdlib.h
   string    - string.h (and legacy strings.h and non-standard nuttx/b2c.h)
@@ -155,5 +156,6 @@ Implementation Details
    :caption: Contents:
    
    search.rst
+   stdbit.rst
    stream.rst
    zoneinfo.rst

Documentation/components/libs/libc/stdbit.rst

@@ -0,0 +1,30 @@
+========
+stdbit.h
+========
+
+The optional C23 ``stdbit.h`` header provides bit manipulation macros
+(endianness, leading/trailing zeros and ones, count, single-bit test,
+bit width, bit floor, bit ceil). NuttX provides this header only when
+explicitly enabled via Kconfig.
+
+Configuration
+=============
+
+- **CONFIG_ARCH_HAVE_STDBIT_H** (bool, selected by arch)
+  Architecture indicates it provides ``arch/<arch>/include/stdbit.h``.
+
+- **CONFIG_ARCH_STDBIT_H** (bool "stdbit.h", depends on ARCH_HAVE_STDBIT_H)
+  Use the redirecting header. The build copies
+  ``include/nuttx/lib/stdbit.h`` to ``include/stdbit.h``; that header
+  then includes ``<arch/stdbit.h>`` when this option is set.
+
+- **CONFIG_LIBC_STDBIT_GENERIC** (bool "stdbit.h (generic C23)")
+  Use the generic C23 implementation. The same redirecting file
+  ``include/nuttx/lib/stdbit.h`` is copied to ``include/stdbit.h``,
+  and the generic implementation is used (no arch header). Requires
+  compiler builtins (e.g. ``__builtin_clz``, ``__builtin_ctz``,
+  ``__builtin_popcount``); see ``CONFIG_HAVE_BUILTIN_*`` in
+  ``nuttx/compiler.h``.
+
+Either **CONFIG_ARCH_STDBIT_H** or **CONFIG_LIBC_STDBIT_GENERIC** may be
+enabled so that ``#include <stdbit.h>`` is available.

Kconfig

@@ -625,6 +625,31 @@ config ARCH_STDARG_H
 		ARCH_STDARG_H=y and providing. If ARCH_STDARG_H, is not defined, then
 		the stdarg.h header file will stay out-of-the-way in include/nuttx/.
 
+config ARCH_HAVE_STDBIT_H
+	bool
+	default n
+	---help---
+		Selected by architecture specific logic if the architecture
+		provides a stdbit.h header file.
+
+config ARCH_STDBIT_H
+	bool "stdbit.h"
+	depends on ARCH_HAVE_STDBIT_H
+	default n
+	---help---
+		Redirecting stdbit.h lives at include/nuttx/lib/stdbit.h. When
+		this is set, the build copies it to include/stdbit.h and it
+		includes arch/stdbit.h if the architecture provides one.
+
+config LIBC_STDBIT_GENERIC
+	bool "stdbit.h (generic C23)"
+	default n
+	---help---
+		Use generic C23 stdbit implementation. When set, copy
+		include/nuttx/lib/stdbit.h to include/stdbit.h. No arch
+		header is used; builtins (e.g. __builtin_clz) must be
+		available (see CONFIG_HAVE_BUILTIN_* in compiler.h).
+
 config ARCH_HAVE_SETJMP
 	bool
 	default n

cmake/nuttx_generate_headers.cmake

@@ -137,6 +137,17 @@ else()
   file(REMOVE ${CMAKE_BINARY_DIR}/include/setjmp.h)
 endif()
 
+# Target used to copy include/nuttx/lib/stdbit.h.  If CONFIG_ARCH_STDBIT_H or
+# CONFIG_LIBC_STDBIT_GENERIC is set, copy stdbit.h to include/ for C23 bit
+# utilities.
+
+if(CONFIG_ARCH_STDBIT_H OR CONFIG_LIBC_STDBIT_GENERIC)
+  nuttx_create_symlink(${NUTTX_DIR}/include/nuttx/lib/stdbit.h
+                       ${CMAKE_BINARY_DIR}/include/stdbit.h)
+else()
+  file(REMOVE ${CMAKE_BINARY_DIR}/include/stdbit.h)
+endif()
+
 # Add final context target that ties together all of the above The context
 # target is invoked on each target build to assure that NuttX is properly
 # configured.  The basic configuration steps include creation of the the
@@ -151,7 +162,10 @@ add_custom_target(
     $<$<BOOL:${CONFIG_ARCH_STDARG_H}>:${CMAKE_BINARY_DIR}/include/stdarg.h>
     $<$<BOOL:${NEED_MATH_H}>:${CMAKE_BINARY_DIR}/include/math.h>
     $<$<BOOL:${CONFIG_ARCH_FLOAT_H}>:${CMAKE_BINARY_DIR}/include/float.h>
-    $<$<BOOL:${CONFIG_ARCH_SETJMP_H}>:${CMAKE_BINARY_DIR}/include/setjmp.h>)
+    $<$<BOOL:${CONFIG_ARCH_SETJMP_H}>:${CMAKE_BINARY_DIR}/include/setjmp.h>
+    $<$<BOOL:${CONFIG_ARCH_STDBIT_H}>:${CMAKE_BINARY_DIR}/include/stdbit.h>
+    $<$<BOOL:${CONFIG_LIBC_STDBIT_GENERIC}>:${CMAKE_BINARY_DIR}/include/stdbit.h>
+)
 
 # apps_context is a PHONY target used as an intermediate process to control the
 # time order of context preparation actions of app building

include/nuttx/lib/stdbit.h

@@ -0,0 +1,485 @@
+/****************************************************************************
+ * include/nuttx/lib/stdbit.h
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to you under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ ****************************************************************************/
+
+#ifndef __INCLUDE_NUTTX_LIB_STDBIT_H
+#define __INCLUDE_NUTTX_LIB_STDBIT_H
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#ifdef CONFIG_ARCH_STDBIT_H
+#  include <arch/stdbit.h>
+#else
+
+#  include <nuttx/compiler.h>
+#  include <stdint.h>
+
+/****************************************************************************
+ * Generic C23 stdbit implementation (CONFIG_LIBC_STDBIT_GENERIC).
+ * Requires __builtin_clz, __builtin_ctz, __builtin_popcount (and ll
+ * variants). If the toolchain does not provide them, enable the
+ * corresponding CONFIG_HAVE_BUILTIN_* in nuttx/compiler.h or do not
+ * use LIBC_STDBIT_GENERIC.
+ ****************************************************************************/
+
+#  if !defined(CONFIG_HAVE_BUILTIN_CLZ) || \
+      !defined(CONFIG_HAVE_BUILTIN_CTZ) || \
+      !defined(CONFIG_HAVE_BUILTIN_POPCOUNT)
+#    error "Generic stdbit requires CONFIG_HAVE_BUILTIN_CLZ, CTZ, POPCOUNT"
+#  endif
+
+#  if defined(CONFIG_HAVE_LONG_LONG) && \
+      !defined(CONFIG_HAVE_BUILTIN_POPCOUNTLL)
+#    error "Generic stdbit 64-bit requires CONFIG_HAVE_BUILTIN_POPCOUNTLL"
+#  endif
+
+/****************************************************************************
+ * C23 endianness macros (reuse LITTLE_ENDIAN/BIG_ENDIAN from sys/endian.h)
+ ****************************************************************************/
+
+#  include <sys/endian.h>
+#  define __STDC_ENDIAN_LITTLE__  LITTLE_ENDIAN
+#  define __STDC_ENDIAN_BIG__     BIG_ENDIAN
+#  define __STDC_ENDIAN_NATIVE__  BYTE_ORDER
+
+/****************************************************************************
+ * Leading / trailing zeros (C23: zero input returns bit width)
+ ****************************************************************************/
+
+static inline unsigned int stdc_leading_zeros_uc(unsigned char x)
+{
+  return (unsigned int)(x == 0 ? (8*sizeof(unsigned char)) :
+         __builtin_clz((unsigned)x << (8*sizeof(unsigned) - 8)));
+}
+
+static inline unsigned int stdc_leading_zeros_us(unsigned short x)
+{
+  return (unsigned int)(x == 0 ? (8*sizeof(unsigned short)) :
+         __builtin_clz((unsigned)x <<
+         (8*sizeof(unsigned) - 16)));
+}
+
+static inline unsigned int stdc_leading_zeros_ui(unsigned int x)
+{
+  return (unsigned int)(x == 0 ? (8*sizeof(unsigned int)) :
+         __builtin_clz(x));
+}
+
+static inline unsigned int stdc_leading_zeros_ul(unsigned long x)
+{
+  return (unsigned int)(x == 0 ? (8*sizeof(unsigned long)) :
+         __builtin_clzl(x));
+}
+
+static inline unsigned int stdc_leading_zeros_ull(unsigned long long x)
+{
+  return (unsigned int)(x == 0 ? (8*sizeof(unsigned long long)) :
+         __builtin_clzll(x));
+}
+
+static inline unsigned int stdc_trailing_zeros_uc(unsigned char x)
+{
+  return (unsigned int)(x == 0 ? (8*sizeof(unsigned char)) :
+         __builtin_ctz((unsigned)x));
+}
+
+static inline unsigned int stdc_trailing_zeros_us(unsigned short x)
+{
+  return (unsigned int)(x == 0 ? (8*sizeof(unsigned short)) :
+         __builtin_ctz((unsigned)x));
+}
+
+static inline unsigned int stdc_trailing_zeros_ui(unsigned int x)
+{
+  return (unsigned int)(x == 0 ? (8*sizeof(unsigned int)) :
+         __builtin_ctz(x));
+}
+
+static inline unsigned int stdc_trailing_zeros_ul(unsigned long x)
+{
+  return (unsigned int)(x == 0 ? (8*sizeof(unsigned long)) :
+         __builtin_ctzl(x));
+}
+
+static inline unsigned int stdc_trailing_zeros_ull(unsigned long long x)
+{
+  return (unsigned int)(x == 0 ? (8*sizeof(unsigned long long)) :
+         __builtin_ctzll(x));
+}
+
+/****************************************************************************
+ * Leading / trailing ones (C23: zero input returns 0)
+ ****************************************************************************/
+
+#  define stdc_leading_ones_uc(x)  stdc_leading_zeros_uc((unsigned char)~(x))
+#  define stdc_leading_ones_us(x)  stdc_leading_zeros_us((unsigned short)~(x))
+#  define stdc_leading_ones_ui(x)  stdc_leading_zeros_ui(~(x))
+#  define stdc_leading_ones_ul(x)  stdc_leading_zeros_ul(~(x))
+#  define stdc_leading_ones_ull(x) stdc_leading_zeros_ull(~(x))
+
+#  define stdc_trailing_ones_uc(x)  \
+    stdc_trailing_zeros_uc((unsigned char)~(x))
+#  define stdc_trailing_ones_us(x)  \
+    stdc_trailing_zeros_us((unsigned short)~(x))
+#  define stdc_trailing_ones_ui(x)  stdc_trailing_zeros_ui(~(x))
+#  define stdc_trailing_ones_ul(x)  stdc_trailing_zeros_ul(~(x))
+#  define stdc_trailing_ones_ull(x) stdc_trailing_zeros_ull(~(x))
+
+/****************************************************************************
+ * First leading zero/one (bit index from MSB; C23: 0 returns bit width)
+ ****************************************************************************/
+
+static inline unsigned int stdc_first_leading_zero_uc(unsigned char x)
+{
+  return (unsigned int)(x == (unsigned char)0xff ? 0 :
+         stdc_leading_ones_uc(x) + 1);
+}
+
+static inline unsigned int stdc_first_leading_zero_us(unsigned short x)
+{
+  return (unsigned int)(x == (unsigned short)0xffff ? 0 :
+         stdc_leading_ones_us(x) + 1);
+}
+
+static inline unsigned int stdc_first_leading_zero_ui(unsigned int x)
+{
+  return (unsigned int)(x == ~0u ? 0 : stdc_leading_ones_ui(x) + 1);
+}
+
+static inline unsigned int stdc_first_leading_zero_ul(unsigned long x)
+{
+  return (unsigned int)(x == ~0ul ? 0 : stdc_leading_ones_ul(x) + 1);
+}
+
+static inline unsigned int stdc_first_leading_zero_ull(unsigned long long x)
+{
+  return (unsigned int)(x == ~0ull ? 0 : stdc_leading_ones_ull(x) + 1);
+}
+
+static inline unsigned int stdc_first_leading_one_uc(unsigned char x)
+{
+  return (unsigned int)(x == 0 ? 0 : stdc_leading_zeros_uc(x) + 1);
+}
+
+static inline unsigned int stdc_first_leading_one_us(unsigned short x)
+{
+  return (unsigned int)(x == 0 ? 0 : stdc_leading_zeros_us(x) + 1);
+}
+
+static inline unsigned int stdc_first_leading_one_ui(unsigned int x)
+{
+  return (unsigned int)(x == 0 ? 0 : stdc_leading_zeros_ui(x) + 1);
+}
+
+static inline unsigned int stdc_first_leading_one_ul(unsigned long x)
+{
+  return (unsigned int)(x == 0 ? 0 : stdc_leading_zeros_ul(x) + 1);
+}
+
+static inline unsigned int stdc_first_leading_one_ull(unsigned long long x)
+{
+  return (unsigned int)(x == 0 ? 0 : stdc_leading_zeros_ull(x) + 1);
+}
+
+/****************************************************************************
+ * First trailing zero/one (bit index from LSB; C23: 0 returns bit width)
+ ****************************************************************************/
+
+static inline unsigned int stdc_first_trailing_zero_uc(unsigned char x)
+{
+  return (unsigned int)(x == (unsigned char)0xff ? 0 :
+         stdc_trailing_ones_uc(x) + 1);
+}
+
+static inline unsigned int stdc_first_trailing_zero_us(unsigned short x)
+{
+  return (unsigned int)(x == (unsigned short)0xffff ? 0 :
+         stdc_trailing_ones_us(x) + 1);
+}
+
+static inline unsigned int stdc_first_trailing_zero_ui(unsigned int x)
+{
+  return (unsigned int)(x == ~0u ? 0 : stdc_trailing_ones_ui(x) + 1);
+}
+
+static inline unsigned int stdc_first_trailing_zero_ul(unsigned long x)
+{
+  return (unsigned int)(x == ~0ul ? 0 : stdc_trailing_ones_ul(x) + 1);
+}
+
+static inline unsigned int stdc_first_trailing_zero_ull(unsigned long long x)
+{
+  return (unsigned int)(x == ~0ull ? 0 : stdc_trailing_ones_ull(x) + 1);
+}
+
+static inline unsigned int stdc_first_trailing_one_uc(unsigned char x)
+{
+  return (unsigned int)(x == 0 ? 0 : stdc_trailing_zeros_uc(x) + 1);
+}
+
+static inline unsigned int stdc_first_trailing_one_us(unsigned short x)
+{
+  return (unsigned int)(x == 0 ? 0 : stdc_trailing_zeros_us(x) + 1);
+}
+
+static inline unsigned int stdc_first_trailing_one_ui(unsigned int x)
+{
+  return (unsigned int)(x == 0 ? 0 : stdc_trailing_zeros_ui(x) + 1);
+}
+
+static inline unsigned int stdc_first_trailing_one_ul(unsigned long x)
+{
+  return (unsigned int)(x == 0 ? 0 : stdc_trailing_zeros_ul(x) + 1);
+}
+
+static inline unsigned int stdc_first_trailing_one_ull(unsigned long long x)
+{
+  return (unsigned int)(x == 0 ? 0 : stdc_trailing_zeros_ull(x) + 1);
+}
+
+/****************************************************************************
+ * Count zeros / ones
+ ****************************************************************************/
+
+#  define stdc_count_ones_uc(x) \
+    ((unsigned int)__builtin_popcount((unsigned)(x)))
+#  define stdc_count_ones_us(x) \
+    ((unsigned int)__builtin_popcount((unsigned)(x)))
+#  define stdc_count_ones_ui(x)  ((unsigned int)__builtin_popcount(x))
+#  define stdc_count_ones_ul(x)  ((unsigned int)__builtin_popcountl(x))
+#  define stdc_count_ones_ull(x) ((unsigned int)__builtin_popcountll(x))
+
+#  define stdc_count_zeros_uc(x) \
+    ((unsigned int)((8*sizeof(unsigned char)) - stdc_count_ones_uc(x)))
+#  define stdc_count_zeros_us(x) \
+    ((unsigned int)((8*sizeof(unsigned short)) - stdc_count_ones_us(x)))
+#  define stdc_count_zeros_ui(x) \
+    ((unsigned int)((8*sizeof(unsigned int)) - stdc_count_ones_ui(x)))
+#  define stdc_count_zeros_ul(x)  \
+    ((unsigned int)((8*sizeof(unsigned long)) - stdc_count_ones_ul(x)))
+#  define stdc_count_zeros_ull(x) \
+    ((unsigned int)((8*sizeof(unsigned long long)) - stdc_count_ones_ull(x)))
+
+/****************************************************************************
+ * Single-bit test, bit width, bit floor, bit ceil
+ ****************************************************************************/
+
+#  define stdc_has_single_bit_uc(x)  (stdc_count_ones_uc(x) == 1)
+#  define stdc_has_single_bit_us(x)   (stdc_count_ones_us(x) == 1)
+#  define stdc_has_single_bit_ui(x)   (stdc_count_ones_ui(x) == 1)
+#  define stdc_has_single_bit_ul(x)   (stdc_count_ones_ul(x) == 1)
+#  define stdc_has_single_bit_ull(x)  (stdc_count_ones_ull(x) == 1)
+
+#  define stdc_bit_width_uc(x) \
+    ((unsigned int)((unsigned char)(x) == 0 ? 0 : \
+    8 - stdc_leading_zeros_uc(x)))
+#  define stdc_bit_width_us(x) \
+    ((unsigned int)((unsigned short)(x) == 0 ? 0 : \
+    16 - stdc_leading_zeros_us(x)))
+#  define stdc_bit_width_ui(x) \
+    ((unsigned int)((x) == 0 ? 0 : \
+    (8*sizeof(unsigned int)) - stdc_leading_zeros_ui(x)))
+#  define stdc_bit_width_ul(x) \
+    ((unsigned int)((x) == 0 ? 0 : \
+    (8*sizeof(unsigned long) - stdc_leading_zeros_ul(x))))
+#  define stdc_bit_width_ull(x) \
+    ((unsigned int)((x) == 0 ? 0 : \
+    (8*sizeof(unsigned long long) - stdc_leading_zeros_ull(x))))
+
+/****************************************************************************
+ * bit_floor / bit_ceil: inline functions to avoid double evaluation of x
+ ****************************************************************************/
+
+static inline unsigned char stdc_bit_floor_uc(unsigned char x)
+{
+  return (unsigned char)(x != 0 ? 1 << ((8*sizeof(unsigned char) - 1) -
+              stdc_leading_zeros_uc(x)) : 0);
+}
+
+static inline unsigned short stdc_bit_floor_us(unsigned short x)
+{
+  return (unsigned short)(x != 0 ? 1 << ((8*sizeof(unsigned short) - 1) -
+              stdc_leading_zeros_us(x)) : 0);
+}
+
+static inline unsigned int stdc_bit_floor_ui(unsigned int x)
+{
+  return x != 0 ? 1u << ((8*sizeof(unsigned int) - 1) -
+              stdc_leading_zeros_ui(x)) : 0u;
+}
+
+static inline unsigned long stdc_bit_floor_ul(unsigned long x)
+{
+  return x != 0 ? (unsigned long)1 << ((8*sizeof(unsigned long) - 1) -
+              stdc_leading_zeros_ul(x)) : 0ul;
+}
+
+static inline unsigned long long stdc_bit_floor_ull(unsigned long long x)
+{
+  return x != 0 ? (unsigned long long)1 << ((8*sizeof(unsigned long long)
+         - 1) - stdc_leading_zeros_ull(x)) : 0ull;
+}
+
+static inline unsigned char stdc_bit_ceil_uc(unsigned char x)
+{
+  return (unsigned char)(x <= 1 ? 1 : (unsigned char)1 <<
+         ((8*sizeof(unsigned char)) -
+          stdc_leading_zeros_uc((unsigned char)(x - 1))));
+}
+
+static inline unsigned short stdc_bit_ceil_us(unsigned short x)
+{
+  return (unsigned short)(x <= 1 ? 1 : (unsigned short)1 <<
+         ((8*sizeof(unsigned short)) -
+          stdc_leading_zeros_us((unsigned short)(x - 1))));
+}
+
+static inline unsigned int stdc_bit_ceil_ui(unsigned int x)
+{
+  return x <= 1 ? 1u : 1u << ((8*sizeof(unsigned int)) -
+         stdc_leading_zeros_ui(x - 1));
+}
+
+static inline unsigned long stdc_bit_ceil_ul(unsigned long x)
+{
+  return x <= 1 ? 1ul : 1ul << ((8*sizeof(unsigned long)) -
+         stdc_leading_zeros_ul(x - 1));
+}
+
+static inline unsigned long long stdc_bit_ceil_ull(unsigned long long x)
+{
+  return x <= 1 ? 1ull : 1ull << ((8*sizeof(unsigned long long)) -
+         stdc_leading_zeros_ull(x - 1));
+}
+
+/****************************************************************************
+ * C23 type-generic macros (dispatch via _Generic)
+ ****************************************************************************/
+
+#  if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
+
+#    define stdc_leading_zeros(x) _Generic((x), \
+        unsigned char: stdc_leading_zeros_uc, \
+        unsigned short: stdc_leading_zeros_us, \
+        unsigned int: stdc_leading_zeros_ui, \
+        unsigned long: stdc_leading_zeros_ul, \
+        unsigned long long: stdc_leading_zeros_ull)(x)
+
+#    define stdc_leading_ones(x) _Generic((x), \
+        unsigned char: stdc_leading_ones_uc, \
+        unsigned short: stdc_leading_ones_us, \
+        unsigned int: stdc_leading_ones_ui, \
+        unsigned long: stdc_leading_ones_ul, \
+        unsigned long long: stdc_leading_ones_ull)(x)
+
+#    define stdc_trailing_zeros(x) _Generic((x), \
+        unsigned char: stdc_trailing_zeros_uc, \
+        unsigned short: stdc_trailing_zeros_us, \
+        unsigned int: stdc_trailing_zeros_ui, \
+        unsigned long: stdc_trailing_zeros_ul, \
+        unsigned long long: stdc_trailing_zeros_ull)(x)
+
+#    define stdc_trailing_ones(x) _Generic((x), \
+        unsigned char: stdc_trailing_ones_uc, \
+        unsigned short: stdc_trailing_ones_us, \
+        unsigned int: 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 int: stdc_first_leading_zero_ui, \
+        unsigned long: stdc_first_leading_zero_ul, \
+        unsigned long long: stdc_first_leading_zero_ull)(x)
+
+#    define stdc_first_leading_one(x) _Generic((x), \
+        unsigned char: stdc_first_leading_one_uc, \
+        unsigned short: stdc_first_leading_one_us, \
+        unsigned int: 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 int: 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 int: stdc_first_trailing_one_ui, \
+        unsigned long: stdc_first_trailing_one_ul, \
+        unsigned long long: stdc_first_trailing_one_ull)(x)
+
+#    define stdc_count_zeros(x) _Generic((x), \
+        unsigned char: stdc_count_zeros_uc, \
+        unsigned short: stdc_count_zeros_us, \
+        unsigned int: stdc_count_zeros_ui, \
+        unsigned long: stdc_count_zeros_ul, \
+        unsigned long long: stdc_count_zeros_ull)(x)
+
+#    define stdc_count_ones(x) _Generic((x), \
+        unsigned char: stdc_count_ones_uc, \
+        unsigned short: stdc_count_ones_us, \
+        unsigned int: stdc_count_ones_ui, \
+        unsigned long: stdc_count_ones_ul, \
+        unsigned long long: stdc_count_ones_ull)(x)
+
+#    define stdc_has_single_bit(x) _Generic((x), \
+        unsigned char: stdc_has_single_bit_uc, \
+        unsigned short: stdc_has_single_bit_us, \
+        unsigned int: stdc_has_single_bit_ui, \
+        unsigned long: stdc_has_single_bit_ul, \
+        unsigned long long: stdc_has_single_bit_ull)(x)
+
+#    define stdc_bit_width(x) _Generic((x), \
+        unsigned char: stdc_bit_width_uc, \
+        unsigned short: stdc_bit_width_us, \
+        unsigned int: stdc_bit_width_ui, \
+        unsigned long: stdc_bit_width_ul, \
+        unsigned long long: stdc_bit_width_ull)(x)
+
+#    define stdc_bit_floor(x) _Generic((x), \
+        unsigned char: stdc_bit_floor_uc, \
+        unsigned short: stdc_bit_floor_us, \
+        unsigned int: stdc_bit_floor_ui, \
+        unsigned long: stdc_bit_floor_ul, \
+        unsigned long long: stdc_bit_floor_ull)(x)
+
+#    define stdc_bit_ceil(x) _Generic((x), \
+        unsigned char: stdc_bit_ceil_uc, \
+        unsigned short: stdc_bit_ceil_us, \
+        unsigned int: stdc_bit_ceil_ui, \
+        unsigned long: stdc_bit_ceil_ul, \
+        unsigned long long: stdc_bit_ceil_ull)(x)
+
+#  endif /* __STDC_VERSION__ >= 201112L */
+
+#endif /* CONFIG_ARCH_STDBIT_H */
+
+#endif /* __INCLUDE_NUTTX_LIB_STDBIT_H */

tools/Unix.mk

@@ -212,6 +212,15 @@ include/stdarg.h: include/nuttx/lib/stdarg.h
 	$(Q) cp -f include/nuttx/lib/stdarg.h include/stdarg.h
 endif
 
+# Target used to copy include/nuttx/lib/stdbit.h.  If CONFIG_ARCH_STDBIT_H or
+# CONFIG_LIBC_STDBIT_GENERIC is set, copy stdbit.h to include/ for C23 bit
+# utilities.
+
+ifeq ($(firstword $(filter y, $(CONFIG_ARCH_STDBIT_H) $(CONFIG_LIBC_STDBIT_GENERIC))),y)
+include/stdbit.h: include/nuttx/lib/stdbit.h
+	$(Q) cp -f include/nuttx/lib/stdbit.h include/stdbit.h
+endif
+
 # Target used to copy include/nuttx/lib/setjmp.h.  If CONFIG_ARCH_SETJMP_H is
 # defined, then there is an architecture specific setjmp.h header file
 # that will be included indirectly from include/lib/setjmp.h.  But first, we
@@ -470,6 +479,10 @@ ifeq ($(CONFIG_ARCH_STDARG_H),y)
 context: include/stdarg.h
 endif
 
+ifeq ($(firstword $(filter y, $(CONFIG_ARCH_STDBIT_H) $(CONFIG_LIBC_STDBIT_GENERIC))),y)
+context: include/stdbit.h
+endif
+
 ifeq ($(CONFIG_ARCH_SETJMP_H),y)
 context: include/setjmp.h
 endif

tools/Win.mk

@@ -194,6 +194,17 @@ else
 include\stdarg.h:
 endif
 
+# Target used to copy include\nuttx\lib\stdbit.h.  If CONFIG_ARCH_STDBIT_H or
+# CONFIG_LIBC_STDBIT_GENERIC is set, copy stdbit.h to include\ for C23 bit
+# utilities.
+
+ifeq ($(firstword $(filter y, $(CONFIG_ARCH_STDBIT_H) $(CONFIG_LIBC_STDBIT_GENERIC))),y)
+include\stdbit.h: include\nuttx\lib\stdbit.h
+	$(Q) cp -f include\nuttx\lib\stdbit.h include\stdbit.h
+else
+include\stdbit.h:
+endif
+
 # Target used to copy include\nuttx\setjmp.h.  If CONFIG_ARCH_SETJMP_H is
 # defined, then there is an architecture specific setjmp.h header file
 # that will be included indirectly from include\setjmp.h.  But first, we
@@ -441,6 +452,10 @@ ifeq ($(CONFIG_ARCH_STDARG_H),y)
 context: include\stdarg.h
 endif
 
+ifeq ($(firstword $(filter y, $(CONFIG_ARCH_STDBIT_H) $(CONFIG_LIBC_STDBIT_GENERIC))),y)
+context: include\stdbit.h
+endif
+
 ifeq ($(CONFIG_ARCH_SETJMP_H),y)
 context: include\setjmp.h
 endif