diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -293,6 +293,7 @@
     libc.src.math.round
     libc.src.math.roundf
     libc.src.math.roundl
+    libc.src.math.signbitf
     libc.src.math.sincosf
     libc.src.math.sinhf
     libc.src.math.sinf
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -295,6 +295,7 @@
     libc.src.math.round
     libc.src.math.roundf
     libc.src.math.roundl
+    libc.src.math.signbitf
     libc.src.math.sin
     libc.src.math.sincosf
     libc.src.math.sinhf
diff --git a/libc/spec/stdc.td b/libc/spec/stdc.td
--- a/libc/spec/stdc.td
+++ b/libc/spec/stdc.td
@@ -464,6 +464,8 @@
           FunctionSpec<"llrintf", RetValSpec<LongLongType>, [ArgSpec<FloatType>]>,
           FunctionSpec<"llrintl", RetValSpec<LongLongType>, [ArgSpec<LongDoubleType>]>,
 
+          FunctionSpec<"signbitf", RetValSpec<BoolType>, [ArgSpec<FloatType>]>,
+
           FunctionSpec<"sqrt", RetValSpec<DoubleType>, [ArgSpec<DoubleType>]>,
           FunctionSpec<"sqrtf", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
           FunctionSpec<"sqrtl", RetValSpec<LongDoubleType>, [ArgSpec<LongDoubleType>]>,
diff --git a/libc/src/__support/FPUtil/ManipulationFunctions.h b/libc/src/__support/FPUtil/ManipulationFunctions.h
--- a/libc/src/__support/FPUtil/ManipulationFunctions.h
+++ b/libc/src/__support/FPUtil/ManipulationFunctions.h
@@ -60,6 +60,11 @@
   }
 }
 
+template <typename T, cpp::enable_if_t<cpp::is_floating_point_v<T>, int> = 0>
+static inline T signbit(T x) {
+  return FPBits<T>(x).get_sign();
+}
+
 template <typename T, cpp::enable_if_t<cpp::is_floating_point_v<T>, int> = 0>
 static inline T copysign(T x, T y) {
   FPBits<T> xbits(x);
diff --git a/libc/src/math/CMakeLists.txt b/libc/src/math/CMakeLists.txt
--- a/libc/src/math/CMakeLists.txt
+++ b/libc/src/math/CMakeLists.txt
@@ -189,6 +189,8 @@
 add_math_entrypoint_object(roundf)
 add_math_entrypoint_object(roundl)
 
+add_math_entrypoint_object(signbitf)
+
 add_math_entrypoint_object(sincosf)
 
 add_math_entrypoint_object(sin)
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -1380,3 +1380,15 @@
   COMPILE_OPTIONS
     -O3
 )
+
+add_entrypoint_object(
+  signbitf
+  SRCS
+    signbitf.cpp
+  HDRS
+    ../signbitf.h
+  DEPENDS
+    libc.src.__support.FPUtil.manipulation_functions
+  COMPILE_OPTIONS
+    -O2
+)
\ No newline at end of file
diff --git a/libc/src/math/generic/signbitf.cpp b/libc/src/math/generic/signbitf.cpp
new file mode 100644
--- /dev/null
+++ b/libc/src/math/generic/signbitf.cpp
@@ -0,0 +1,17 @@
+//===-- Implementation of signbitf 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/signbitf.h"
+#include "src/__support/FPUtil/ManipulationFunctions.h"
+#include "src/__support/common.h"
+
+namespace __llvm_libc {
+
+LLVM_LIBC_FUNCTION(bool, signbitf, (float x)) { return fputil::signbit(x); }
+
+} // namespace __llvm_libc
diff --git a/libc/src/math/signbitf.h b/libc/src/math/signbitf.h
new file mode 100644
--- /dev/null
+++ b/libc/src/math/signbitf.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for signbitf ----------------------*- 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_SIGNBITF_H
+#define LLVM_LIBC_SRC_MATH_SIGNBITF_H
+
+namespace __llvm_libc {
+
+bool signbitf(float x);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_MATH_SIGNBITF_H
diff --git a/libc/test/src/math/CMakeLists.txt b/libc/test/src/math/CMakeLists.txt
--- a/libc/test/src/math/CMakeLists.txt
+++ b/libc/test/src/math/CMakeLists.txt
@@ -1529,9 +1529,24 @@
   SRCS
     pow_test.cpp
   DEPENDS
-  libc.include.errno
-  libc.src.errno.errno
-  libc.src.math.pow
+    libc.include.errno
+    libc.src.errno.errno
+    libc.src.math.pow
+)
+
+add_fp_unittest(
+  signbitf_test
+  NEED_MPFR
+  SUITE
+    libc_math_unittests
+  SRCS
+    signbitf_test.cpp
+  HDRS
+    SignBitTest.h
+  DEPENDS
+    libc.include.math
+    libc.src.math.signbitf
+    libc.src.__support.FPUtil.fp_bits
 )
 
 add_subdirectory(generic)
diff --git a/libc/test/src/math/SignBitTest.h b/libc/test/src/math/SignBitTest.h
new file mode 100644
--- /dev/null
+++ b/libc/test/src/math/SignBitTest.h
@@ -0,0 +1,51 @@
+//===-- Utility class to test signbit[f|l] ----------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "utils/MPFRWrapper/MPFRUtils.h"
+#include "utils/UnitTest/FPMatcher.h"
+#include "utils/UnitTest/Test.h"
+
+#include <math.h>
+
+namespace mpfr = __llvm_libc::testing::mpfr;
+
+template <typename T> class SignBitTest : public __llvm_libc::testing::Test {
+
+  DECLARE_SPECIAL_CONSTANTS(T)
+
+public:
+  typedef bool (*SignBitFunc)(T);
+
+  void testSpecialNumbers(SignBitFunc func) {
+    EXPECT_EQ(true, func(-1.0));
+    EXPECT_EQ(false, func(1.0));
+
+    EXPECT_EQ(true, func(neg_inf));
+    EXPECT_EQ(false, func(inf));
+
+    EXPECT_EQ(true, func(neg_zero));
+    EXPECT_EQ(false, func(zero));
+  }
+
+  void testRange(SignBitFunc func) {
+    constexpr UIntType COUNT = 10000000;
+    constexpr UIntType STEP = UIntType(-1) / COUNT;
+    for (UIntType i = 0, v = 0; i <= COUNT; ++i, v += STEP) {
+      T x = T(FPBits(v));
+      if (isnan(x) || isinf(x))
+        continue;
+
+      ASSERT_EQ(mpfr::signbit(x), func(x));
+    }
+  }
+};
+
+#define LIST_SIGNBIT_TESTS(T, func)                                            \
+  using LlvmLibcSignBitTest = SignBitTest<T>;                                  \
+  TEST_F(LlvmLibcSignBitTest, SpecialNumbers) { testSpecialNumbers(&func); }   \
+  TEST_F(LlvmLibcSignBitTest, Range) { testRange(&func); }
diff --git a/libc/test/src/math/signbitf_test.cpp b/libc/test/src/math/signbitf_test.cpp
new file mode 100644
--- /dev/null
+++ b/libc/test/src/math/signbitf_test.cpp
@@ -0,0 +1,13 @@
+//===-- Unittests for copysignf -------------------------------------------===//
+//
+// 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 "SignBitTest.h"
+
+#include "src/math/signbitf.h"
+
+LIST_SIGNBIT_TESTS(float, __llvm_libc::signbitf)
diff --git a/libc/utils/MPFRWrapper/MPFRUtils.h b/libc/utils/MPFRWrapper/MPFRUtils.h
--- a/libc/utils/MPFRWrapper/MPFRUtils.h
+++ b/libc/utils/MPFRWrapper/MPFRUtils.h
@@ -316,6 +316,8 @@
 template <typename T> bool round_to_long(T x, long &result);
 template <typename T> bool round_to_long(T x, RoundingMode mode, long &result);
 
+template <typename T> bool signbit(T x);
+
 } // namespace mpfr
 } // namespace testing
 } // namespace __llvm_libc
diff --git a/libc/utils/MPFRWrapper/MPFRUtils.cpp b/libc/utils/MPFRWrapper/MPFRUtils.cpp
--- a/libc/utils/MPFRWrapper/MPFRUtils.cpp
+++ b/libc/utils/MPFRWrapper/MPFRUtils.cpp
@@ -363,6 +363,10 @@
     return result;
   }
 
+  bool signbit() const {
+    return mpfr_signbit(value);
+  }
+
   MPFRNumber sin() const {
     MPFRNumber result(*this);
     mpfr_sin(result.value, value, mpfr_rounding);
@@ -1022,6 +1026,15 @@
 template double round<double>(double, RoundingMode);
 template long double round<long double>(long double, RoundingMode);
 
+template <typename T> bool signbit(T x) {
+  MPFRNumber mpfr(x);
+  return mpfr.signbit();
+}
+
+template bool signbit<float>(float);
+template bool signbit<double>(double);
+template bool signbit<long double>(long double);
+
 } // namespace mpfr
 } // namespace testing
 } // namespace __llvm_libc