diff --git a/libc/test/src/math/exhaustive/cospif_test.cpp b/libc/test/src/math/exhaustive/cospif_test.cpp
@@ -0,0 +1,33 @@
+//===-- Exhaustive test for cospif ----------------------------------------===//
+//
+// 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 "exhaustive_test.h"
+#include "src/math/cospif.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+
+namespace mpfr = LIBC_NAMESPACE::testing::mpfr;
+
+using LlvmLibcCospifExhaustiveTest =
+    LlvmLibcUnaryOpExhaustiveMathTest<float, mpfr::Operation::Cospi,
+                                      LIBC_NAMESPACE::cospif>;
+
+static constexpr uint32_t POS_START = 0x0000'0000U;
+static constexpr uint32_t POS_STOP = 0x7f80'0000U;
+
+// Range: [0, Inf]
+TEST_F(LlvmLibcCospifExhaustiveTest, PostiveRange) {
+  test_full_range_all_roundings(POS_START, POS_STOP);
+}
+
+// Range: [-Inf, 0]
+static constexpr uint32_t NEG_START = 0xb000'0000U;
+static constexpr uint32_t NEG_STOP = 0xff80'0000U;
+
+TEST_F(LlvmLibcCospifExhaustiveTest, NegativeRange) {
+  test_full_range_all_roundings(NEG_START, NEG_STOP);
+}
diff --git a/libc/test/src/math/smoke/CMakeLists.txt b/libc/test/src/math/smoke/CMakeLists.txt
@@ -10,6 +10,17 @@ add_fp_unittest(
   DEPENDS
     libc.src.errno.errno
     libc.src.math.cosf
+)
+
+add_fp_unittest(
+  cospif_test
+  SUITE
+    libc-math-smoke-tests
+  SRCS
+    cospif_test.cpp
+  DEPENDS
+    libc.src.errno.errno
+    libc.src.math.cospif
     libc.src.__support.CPP.array
     libc.src.__support.FPUtil.fp_bits
 )

diff --git a/libc/test/src/math/smoke/cospif_test.cpp b/libc/test/src/math/smoke/cospif_test.cpp
@@ -0,0 +1,34 @@
+//===-- Unittests for cospif ----------------------------------------------===//
+//
+// 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/errno/libc_errno.h"
+#include "src/math/cospif.h"
+#include "test/UnitTest/FPMatcher.h"
+
+#include <stdint.h>
+
+using LlvmLibcCospifTest = LIBC_NAMESPACE::testing::FPTest<float>;
+
+TEST_F(LlvmLibcCospifTest, SpecialNumbers) {
+  LIBC_NAMESPACE::libc_errno = 0;
+
+  EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::cospif(aNaN));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ(1.0f, LIBC_NAMESPACE::cospif(0.0f));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ(1.0f, LIBC_NAMESPACE::cospif(-0.0f));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::cospif(inf));
+  EXPECT_MATH_ERRNO(EDOM);
+
+  EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::cospif(neg_inf));
+  EXPECT_MATH_ERRNO(EDOM);
+}
diff --git a/libc/utils/MPFRWrapper/MPFRUtils.cpp b/libc/utils/MPFRWrapper/MPFRUtils.cpp
@@ -239,6 +239,39 @@ class MPFRNumber {
     return result;
   }
 
+  MPFRNumber cospi() const {
+    MPFRNumber result(*this);
+
+#if MPFR_VERSION_MAJOR > 4 ||                                                  \
+    (MPFR_VERSION_MAJOR == 4 && MPFR_VERSION_MINOR >= 2)
+    mpfr_cospi(result.value, value, mpfr_rounding);
+    return result;
+#else
+    MPFRNumber value_frac(*this);
+    mpfr_frac(value_frac.value, value, MPFR_RNDN);
+
+    if (mpfr_cmp_si(value_frac.value, 0.0) == 0) {
+      mpz_t integer_part;
+      mpz_init(integer_part);
+      mpfr_get_z(integer_part, value, MPFR_RNDN);
+
+      if (mpz_tstbit(integer_part, 0)) {
+        mpfr_set_si(result.value, -1.0, MPFR_RNDN); // odd
+      } else {
+        mpfr_set_si(result.value, 1.0, MPFR_RNDN); // even
+      }
+      return result;
+    }
+
+    MPFRNumber value_pi(0.0, 1280);
+    mpfr_const_pi(value_pi.value, MPFR_RNDN);
+    mpfr_mul(value_pi.value, value_pi.value, value, MPFR_RNDN);
+    mpfr_cos(result.value, value_pi.value, mpfr_rounding);
+
+    return result;
+#endif
+  }
+
   MPFRNumber erf() const {
     MPFRNumber result(*this);
     mpfr_erf(result.value, value, mpfr_rounding);
@@ -675,6 +708,8 @@ unary_operation(Operation op, InputType input, unsigned int precision,
     return mpfrInput.cos();
   case Operation::Cosh:
     return mpfrInput.cosh();
+  case Operation::Cospi:
+    return mpfrInput.cospi();
   case Operation::Erf:
     return mpfrInput.erf();
   case Operation::Exp:

diff --git a/libc/utils/MPFRWrapper/MPFRUtils.h b/libc/utils/MPFRWrapper/MPFRUtils.h
@@ -34,6 +34,7 @@ enum class Operation : int {
   Ceil,
   Cos,
   Cosh,
+  Cospi,
   Erf,
   Exp,
   Exp2,
-Original file line number
+Diff line change
@@ Expand Up / @@ -34,6 +34,7 @@ enum class Operation : int { @@
       Ceil,
       Cos,
       Cosh,
+      Cospi,
       Erf,
       Exp,
       Exp2,
@@ Expand Down @@