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

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This PR adds the nanbf16 basic math function for BFloat16 type along with the tests.

@krishna2803
feat: implement nanbf16 math function
ea9625e 
Signed-off-by: Krishna Pandey <kpandey81930@gmail.com>
@krishna2803
chore: add smoke tests for nanbf16 math function
ae0e616 
Signed-off-by: Krishna Pandey <kpandey81930@gmail.com>
@krishna2803
chore: update entrypoints
27364c5 
Signed-off-by: Krishna Pandey <kpandey81930@gmail.com>
@krishna2803
docs: add nanbf16
250cfea 
Signed-off-by: Krishna Pandey <kpandey81930@gmail.com>
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llvmbot commented Aug 17, 2025 •
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@llvm/pr-subscribers-backend-risc-v

@llvm/pr-subscribers-libc

Author: Krishna Pandey (krishna2803)

Changes

This PR adds the nanbf16 basic math function for BFloat16 type along with the tests.

Full diff: https://github.com/llvm/llvm-project/pull/153995.diff

19 Files Affected:

  • (modified) libc/config/baremetal/aarch64/entrypoints.txt (+1)
  • (modified) libc/config/baremetal/arm/entrypoints.txt (+1)
  • (modified) libc/config/baremetal/riscv/entrypoints.txt (+1)
  • (modified) libc/config/darwin/aarch64/entrypoints.txt (+1)
  • (modified) libc/config/darwin/x86_64/entrypoints.txt (+1)
  • (modified) libc/config/gpu/amdgpu/entrypoints.txt (+1)
  • (modified) libc/config/gpu/nvptx/entrypoints.txt (+1)
  • (modified) libc/config/linux/aarch64/entrypoints.txt (+1)
  • (modified) libc/config/linux/arm/entrypoints.txt (+1)
  • (modified) libc/config/linux/riscv/entrypoints.txt (+1)
  • (modified) libc/config/linux/x86_64/entrypoints.txt (+1)
  • (modified) libc/config/windows/entrypoints.txt (+1)
  • (modified) libc/docs/headers/math/index.rst (+1-1)
  • (modified) libc/src/math/CMakeLists.txt (+1)
  • (modified) libc/src/math/generic/CMakeLists.txt (+16)
  • (added) libc/src/math/generic/nanbf16.cpp (+25)
  • (added) libc/src/math/nanbf16.h (+21)
  • (modified) libc/test/src/math/smoke/CMakeLists.txt (+16)
  • (added) libc/test/src/math/smoke/nanbf16_test.cpp (+55)
diff --git a/libc/config/baremetal/aarch64/entrypoints.txt b/libc/config/baremetal/aarch64/entrypoints.txt
index 5f72793beecb4..c4ec03fc146e8 100644
--- 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
index 244dd2e87b1fd..d9e173a71e47a 100644
--- 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
index 32980c4a1d222..9b0cf14037fae 100644
--- 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
index 3684713474cbc..2a634852a2ed0 100644
--- 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
index 7482a80c37d33..6a18d557f86fb 100644
--- 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
index a88c74be2997a..008f7c7bd642c 100644
--- 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
index 08e6c7dc34b07..ae434117eb8e2 100644
--- a/libc/config/gpu/nvptx/entrypoints.txt
+++ b/libc/config/gpu/nvptx/entrypoints.txt
@@ -648,6 +648,7 @@ 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
index ea7e2065b2216..88438247643f6 100644
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -875,6 +875,7 @@ 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
index 8f21976e9e88e..865392a918624 100644
--- 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
index 69d7519118198..207608c431a9b 100644
--- 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
index 75dcfd6382f1b..44f5f2d03db0a 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -926,6 +926,7 @@ 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
index 541d9fee1adf5..32a6a578aae13 100644
--- 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
index d8921b985b1f2..9efbce06920b5 100644
--- 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/math/CMakeLists.txt b/libc/src/math/CMakeLists.txt
index 023829b21996f..87a341bb6267b 100644
--- a/libc/src/math/CMakeLists.txt
+++ b/libc/src/math/CMakeLists.txt
@@ -420,6 +420,7 @@ 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
index 38ba34ae521ea..e34e3f04ed8bd 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -3444,6 +3444,22 @@ 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
new file mode 100644
index 0000000000000..678dd6aed9ee3
--- /dev/null
+++ 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
new file mode 100644
index 0000000000000..1551044677768
--- /dev/null
+++ 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
index 8c257664dd8d7..c26bd84e2ca9d 100644
--- 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
new file mode 100644
index 0000000000000..4154f6ed637c8
--- /dev/null
+++ 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

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@krishna2803 @llvmbot