[libc][math][c++23] Add nanbf16 math function (#153995)

krishna2803 · web-flow · commit 699f15426fae · 2025-08-23T14:45:53.000+05:30
This PR adds the nanbf16 basic math function for BFloat16 type along
with the tests.

---------

Signed-off-by: Krishna Pandey &lt;kpandey81930@gmail.com&gt;
diff --git a/libc/config/baremetal/aarch64/entrypoints.txt b/libc/config/baremetal/aarch64/entrypoints.txt
@@ -788,6 +788,7 @@ list(APPEND TARGET_LIBM_ENTRYPOINTS
   libc.src.math.fromfpbf16
   libc.src.math.fromfpxbf16
   libc.src.math.getpayloadbf16
+  libc.src.math.nanbf16
   libc.src.math.nextafterbf16
   libc.src.math.nextdownbf16
   libc.src.math.nexttowardbf16
diff --git a/libc/config/baremetal/arm/entrypoints.txt b/libc/config/baremetal/arm/entrypoints.txt
@@ -791,6 +791,7 @@ list(APPEND TARGET_LIBM_ENTRYPOINTS
   libc.src.math.fromfpbf16
   libc.src.math.fromfpxbf16
   libc.src.math.getpayloadbf16
+  libc.src.math.nanbf16
   libc.src.math.nextafterbf16
   libc.src.math.nextdownbf16
   libc.src.math.nexttowardbf16
diff --git a/libc/config/baremetal/riscv/entrypoints.txt b/libc/config/baremetal/riscv/entrypoints.txt
@@ -791,6 +791,7 @@ list(APPEND TARGET_LIBM_ENTRYPOINTS
   libc.src.math.fromfpbf16
   libc.src.math.fromfpxbf16
   libc.src.math.getpayloadbf16
+  libc.src.math.nanbf16
   libc.src.math.nextafterbf16
   libc.src.math.nextdownbf16
   libc.src.math.nexttowardbf16
diff --git a/libc/config/darwin/aarch64/entrypoints.txt b/libc/config/darwin/aarch64/entrypoints.txt
@@ -621,6 +621,7 @@ list(APPEND TARGET_LIBM_ENTRYPOINTS
   libc.src.math.fromfpbf16
   libc.src.math.fromfpxbf16
   libc.src.math.getpayloadbf16
+  libc.src.math.nanbf16
   libc.src.math.nextafterbf16
   libc.src.math.nextdownbf16
   libc.src.math.nexttowardbf16
diff --git a/libc/config/darwin/x86_64/entrypoints.txt b/libc/config/darwin/x86_64/entrypoints.txt
@@ -264,6 +264,7 @@ list(APPEND TARGET_LIBM_ENTRYPOINTS
   libc.src.math.fromfpbf16
   libc.src.math.fromfpxbf16
   libc.src.math.getpayloadbf16
+  libc.src.math.nanbf16
   libc.src.math.nextafterbf16
   libc.src.math.nextdownbf16
   libc.src.math.nexttowardbf16
diff --git a/libc/config/gpu/amdgpu/entrypoints.txt b/libc/config/gpu/amdgpu/entrypoints.txt
@@ -647,6 +647,7 @@ list(APPEND TARGET_LIBM_ENTRYPOINTS
   libc.src.math.fromfpbf16
   libc.src.math.fromfpxbf16
   libc.src.math.getpayloadbf16
+  libc.src.math.nanbf16
   libc.src.math.nextafterbf16
   libc.src.math.nextdownbf16
   libc.src.math.nexttowardbf16
diff --git a/libc/config/gpu/nvptx/entrypoints.txt b/libc/config/gpu/nvptx/entrypoints.txt
@@ -649,6 +649,7 @@ list(APPEND TARGET_LIBM_ENTRYPOINTS
   libc.src.math.fromfpbf16
   libc.src.math.fromfpxbf16
   libc.src.math.getpayloadbf16
+  libc.src.math.nanbf16
   libc.src.math.nextafterbf16
   libc.src.math.nextdownbf16
   libc.src.math.nexttowardbf16
diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
@@ -876,6 +876,7 @@ list(APPEND TARGET_LIBM_ENTRYPOINTS
   libc.src.math.fromfpbf16
   libc.src.math.fromfpxbf16
   libc.src.math.getpayloadbf16
+  libc.src.math.nanbf16
   libc.src.math.nextafterbf16
   libc.src.math.nextdownbf16
   libc.src.math.nexttowardbf16
diff --git a/libc/config/linux/arm/entrypoints.txt b/libc/config/linux/arm/entrypoints.txt
@@ -491,6 +491,7 @@ list(APPEND TARGET_LIBM_ENTRYPOINTS
   libc.src.math.fromfpbf16
   libc.src.math.fromfpxbf16
   libc.src.math.getpayloadbf16
+  libc.src.math.nanbf16
   libc.src.math.nextafterbf16
   libc.src.math.nextdownbf16
   libc.src.math.nexttowardbf16
diff --git a/libc/config/linux/riscv/entrypoints.txt b/libc/config/linux/riscv/entrypoints.txt
@@ -894,6 +894,7 @@ list(APPEND TARGET_LIBM_ENTRYPOINTS
   libc.src.math.fromfpbf16
   libc.src.math.fromfpxbf16
   libc.src.math.getpayloadbf16
+  libc.src.math.nanbf16
   libc.src.math.nextafterbf16
   libc.src.math.nextdownbf16
   libc.src.math.nexttowardbf16
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
@@ -927,6 +927,7 @@ list(APPEND TARGET_LIBM_ENTRYPOINTS
   libc.src.math.fromfpbf16
   libc.src.math.fromfpxbf16
   libc.src.math.getpayloadbf16
+  libc.src.math.nanbf16
   libc.src.math.nextafterbf16
   libc.src.math.nextdownbf16
   libc.src.math.nexttowardbf16
diff --git a/libc/config/windows/entrypoints.txt b/libc/config/windows/entrypoints.txt
@@ -337,6 +337,7 @@ list(APPEND TARGET_LIBM_ENTRYPOINTS
   libc.src.math.fromfpbf16
   libc.src.math.fromfpxbf16
   libc.src.math.getpayloadbf16
+  libc.src.math.nanbf16
   libc.src.math.nextafterbf16
   libc.src.math.nextdownbf16
   libc.src.math.nexttowardbf16
diff --git a/libc/docs/headers/math/index.rst b/libc/docs/headers/math/index.rst
@@ -211,7 +211,7 @@ Basic Operations
 +------------------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+------------------------+----------------------------+
 | modf             | |check|          | |check|         | |check|                | |check|              | |check|                |                        | 7.12.6.18              | F.10.3.18                  |
 +------------------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+------------------------+----------------------------+
-| nan              | |check|          | |check|         | |check|                | |check|              | |check|                |                        | 7.12.11.2              | F.10.8.2                   |
+| nan              | |check|          | |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                   |
 +------------------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+------------------------+----------------------------+
diff --git a/libc/src/__support/FPUtil/BasicOperations.h b/libc/src/__support/FPUtil/BasicOperations.h
@@ -354,7 +354,10 @@ LIBC_INLINE cpp::enable_if_t<cpp::is_floating_point_v<T>, T> getpayload(T x) {
 
     return static_cast<T>(payload_dfloat);
   } else {
-    return static_cast<T>(payload);
+    if constexpr (cpp::is_same_v<T, bfloat16>)
+      return T(static_cast<int>(payload));
+    else
+      return static_cast<T>(payload);
   }
 }
 
diff --git a/libc/src/math/CMakeLists.txt b/libc/src/math/CMakeLists.txt
@@ -422,6 +422,7 @@ add_math_entrypoint_object(nanf)
 add_math_entrypoint_object(nanl)
 add_math_entrypoint_object(nanf16)
 add_math_entrypoint_object(nanf128)
+add_math_entrypoint_object(nanbf16)
 
 add_math_entrypoint_object(nearbyint)
 add_math_entrypoint_object(nearbyintf)
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
@@ -3432,6 +3432,22 @@ add_entrypoint_object(
     libc.src.errno.errno
 )
 
+add_entrypoint_object(
+  nanbf16
+  SRCS
+    nanbf16.cpp
+  HDRS
+    ../nanbf16.h
+  DEPENDS
+    libc.src.errno.errno
+    libc.src.__support.common
+    libc.src.__support.FPUtil.bfloat16
+    libc.src.__support.libc_errno
+    libc.src.__support.macros.config
+    libc.src.__support.macros.properties.types
+    libc.src.__support.str_to_float
+)
+
 add_entrypoint_object(
   nextafter
   SRCS
diff --git a/libc/src/math/generic/nanbf16.cpp b/libc/src/math/generic/nanbf16.cpp
@@ -0,0 +1,25 @@
+//===-- Implementation of nanbf16 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/nanbf16.h"
+#include "src/__support/FPUtil/bfloat16.h"
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/str_to_float.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(bfloat16, nanbf16, (const char *arg)) {
+  auto result = internal::strtonan<bfloat16>(arg);
+  if (result.has_error())
+    libc_errno = result.error;
+  return result.value;
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/math/nanbf16.h b/libc/src/math/nanbf16.h
@@ -0,0 +1,21 @@
+//===-- Implementation header for nanbf16 -----------------------*- 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_NANBF16_H
+#define LLVM_LIBC_SRC_MATH_NANBF16_H
+
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/properties/types.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+bfloat16 nanbf16(const char *arg);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_MATH_NANBF16_H
diff --git a/libc/test/src/math/smoke/CMakeLists.txt b/libc/test/src/math/smoke/CMakeLists.txt
@@ -3515,6 +3515,22 @@ add_fp_unittest(
   UNIT_TEST_ONLY
 )
 
+add_fp_unittest(
+  nanbf16_test
+  SUITE
+    libc-math-smoke-tests
+  SRCS
+    nanbf16_test.cpp
+  DEPENDS
+    libc.hdr.signal_macros
+    libc.src.math.nanbf16
+    libc.src.__support.FPUtil.bfloat16
+    libc.src.__support.FPUtil.fp_bits
+  # FIXME: The nan tests currently have death tests, which aren't supported for
+  # hermetic tests.
+  UNIT_TEST_ONLY
+)
+
 add_fp_unittest(
   nearbyint_test
   SUITE
diff --git a/libc/test/src/math/smoke/nanbf16_test.cpp b/libc/test/src/math/smoke/nanbf16_test.cpp
@@ -0,0 +1,55 @@
+//===-- Unittests for nanbf16 ---------------------------------------------===//
+//
+// 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 "hdr/signal_macros.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/bfloat16.h"
+#include "src/math/nanbf16.h"
+#include "test/UnitTest/FEnvSafeTest.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+
+class LlvmLibcNanf16Test : public LIBC_NAMESPACE::testing::FEnvSafeTest {
+public:
+  using StorageType = LIBC_NAMESPACE::fputil::FPBits<bfloat16>::StorageType;
+
+  void run_test(const char *input_str, StorageType bits) {
+    bfloat16 result = LIBC_NAMESPACE::nanbf16(input_str);
+    auto actual_fp = LIBC_NAMESPACE::fputil::FPBits<bfloat16>(result);
+    auto expected_fp = LIBC_NAMESPACE::fputil::FPBits<bfloat16>(bits);
+    EXPECT_EQ(actual_fp.uintval(), expected_fp.uintval());
+  }
+};
+
+TEST_F(LlvmLibcNanf16Test, NCharSeq) {
+  run_test("", 0x7fc0);
+
+  // 0x7fc0 + 0x1f (31) = 0x7cdf
+  run_test("31", 0x7fdf);
+
+  // 0x7fc0 + 0x15 = 0x7fd5
+  run_test("0x15", 0x7fd5);
+
+  run_test("1a", 0x7fc0);
+  run_test("1234567890qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM_",
+           0x7fc0);
+  run_test("10000000000000000000000000000", 0x7fc0);
+}
+
+TEST_F(LlvmLibcNanf16Test, RandomString) {
+  run_test(" 1234", 0x7fc0);
+  run_test("-1234", 0x7fc0);
+  run_test("asd&f", 0x7fc0);
+  run_test("123 ", 0x7fc0);
+}
+
+#if defined(LIBC_ADD_NULL_CHECKS)
+TEST_F(LlvmLibcNanf16Test, InvalidInput) {
+  EXPECT_DEATH([] { LIBC_NAMESPACE::nanbf16(nullptr); }, WITH_SIGNAL(-1));
+}
+#endif // LIBC_ADD_NULL_CHECKS
