[libc][math][c23] Add nanf16 C23 math function (#94767)

Part of #93566.

Author: overmighty

libc/config/linux/aarch64/entrypoints.txt

@@ -522,6 +522,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
     libc.src.math.llroundf16
     libc.src.math.lrintf16
     libc.src.math.lroundf16
+    libc.src.math.nanf16
     libc.src.math.nearbyintf16
     libc.src.math.nextafterf16
     libc.src.math.nextdownf16

libc/config/linux/x86_64/entrypoints.txt

@@ -555,6 +555,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
     libc.src.math.llroundf16
     libc.src.math.lrintf16
     libc.src.math.lroundf16
+    libc.src.math.nanf16
     libc.src.math.nearbyintf16
     libc.src.math.nextafterf16
     libc.src.math.nextdownf16

libc/docs/math/index.rst

@@ -186,7 +186,7 @@ Basic Operations
 +------------------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
 | modf             | |check|          | |check|         | |check|                |                      | |check|                | 7.12.6.18              | F.10.3.18                  |
 +------------------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
-| nan              | |check|          | |check|         | |check|                |                      | |check|                | 7.12.11.2              | F.10.8.2                   |
+| nan              | |check|          | |check|         | |check|                | |check|              | |check|                | 7.12.11.2              | F.10.8.2                   |
 +------------------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
 | nearbyint        | |check|          | |check|         | |check|                | |check|              | |check|                | 7.12.9.3               | F.10.6.3                   |
 +------------------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+

libc/include/llvm-libc-types/CMakeLists.txt

@@ -58,7 +58,7 @@ add_header(pthread_rwlockattr_t HDR pthread_rwlockattr_t.h)
 add_header(pthread_t HDR pthread_t.h DEPENDS .__thread_type)
 add_header(rlim_t HDR rlim_t.h)
 add_header(time_t HDR time_t.h)
-add_header(stack_t HDR stack_t.h)
+add_header(stack_t HDR stack_t.h DEPENDS .size_t)
 add_header(suseconds_t HDR suseconds_t.h)
 add_header(struct_flock HDR struct_flock.h DEPENDS .off_t .pid_t)
 add_header(struct_flock64 HDR struct_flock64.h DEPENDS .off64_t .pid_t)

libc/spec/stdc.td

@@ -695,6 +695,7 @@ def StdC : StandardSpec<"stdc"> {
           FunctionSpec<"nanf", RetValSpec<FloatType>, [ArgSpec<ConstCharPtr>]>,
           FunctionSpec<"nan", RetValSpec<DoubleType>, [ArgSpec<ConstCharPtr>]>,
           FunctionSpec<"nanl", RetValSpec<LongDoubleType>, [ArgSpec<ConstCharPtr>]>,
+          GuardedFunctionSpec<"nanf16", RetValSpec<Float16Type>, [ArgSpec<ConstCharPtr>], "LIBC_TYPES_HAS_FLOAT16">,
           GuardedFunctionSpec<"nanf128", RetValSpec<Float128Type>, [ArgSpec<ConstCharPtr>], "LIBC_TYPES_HAS_FLOAT128">,
 
           FunctionSpec<"canonicalize", RetValSpec<IntType>, [ArgSpec<DoubleType>, ArgSpec<DoubleType>]>,

libc/src/math/CMakeLists.txt

@@ -272,6 +272,7 @@ add_math_entrypoint_object(modff128)
 add_math_entrypoint_object(nan)
 add_math_entrypoint_object(nanf)
 add_math_entrypoint_object(nanl)
+add_math_entrypoint_object(nanf16)
 add_math_entrypoint_object(nanf128)
 
 add_math_entrypoint_object(nearbyint)

libc/src/math/generic/CMakeLists.txt

@@ -2631,6 +2631,19 @@ add_entrypoint_object(
     -O3
 )
 
+add_entrypoint_object(
+  nanf16
+  SRCS
+    nanf16.cpp
+  HDRS
+    ../nanf16.h
+  DEPENDS
+    libc.src.__support.str_to_float
+    libc.src.errno.errno
+  COMPILE_OPTIONS
+    -O3
+)
+
 add_entrypoint_object(
   nanf128
   SRCS

libc/src/math/generic/nanf16.cpp

@@ -0,0 +1,23 @@
+//===-- Implementation of nanf16 function ---------------------------------===//
+//
+// 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/math/nanf16.h"
+#include "src/__support/common.h"
+#include "src/__support/str_to_float.h"
+#include "src/errno/libc_errno.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(float16, nanf16, (const char *arg)) {
+  auto result = internal::strtonan<float16>(arg);
+  if (result.has_error())
+    libc_errno = result.error;
+  return result.value;
+}
+
+} // namespace LIBC_NAMESPACE

libc/src/math/nanf16.h

@@ -0,0 +1,20 @@
+//===-- Implementation header for nanf16 ------------------------*- 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_MATH_NANF16_H
+#define LLVM_LIBC_SRC_MATH_NANF16_H
+
+#include "src/__support/macros/properties/types.h"
+
+namespace LIBC_NAMESPACE {
+
+float16 nanf16(const char *arg);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_MATH_NANF16_H

libc/test/src/math/smoke/CMakeLists.txt

@@ -2636,6 +2636,22 @@ add_fp_unittest(
   UNIT_TEST_ONLY
 )
 
+add_fp_unittest(
+  nanf16_test
+  SUITE
+    libc-math-smoke-tests
+  SRCS
+    nanf16_test.cpp
+  DEPENDS
+    libc.include.signal
+    libc.src.math.nanf16
+    libc.src.__support.FPUtil.fp_bits
+    libc.src.__support.macros.sanitizer
+  # FIXME: The nan tests currently have death tests, which aren't supported for
+  # hermetic tests.
+  UNIT_TEST_ONLY
+)
+
 add_fp_unittest(
   nanf128_test
   SUITE