diff --git a/libc/test/src/math/acosf_test.cpp b/libc/test/src/math/acosf_test.cpp
@@ -0,0 +1,75 @@
+//===-- Unittests for acosf -----------------------------------------------===//
+//
+// 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/__support/FPUtil/FPBits.h"
+#include "src/math/acosf.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+#include "utils/UnitTest/FPMatcher.h"
+#include "utils/UnitTest/Test.h"
+#include <math.h>
+
+#include <errno.h>
+#include <stdint.h>
+
+using FPBits = __llvm_libc::fputil::FPBits<float>;
+
+namespace mpfr = __llvm_libc::testing::mpfr;
+
+DECLARE_SPECIAL_CONSTANTS(float)
+
+TEST(LlvmLibcAcosfTest, SpecialNumbers) {
+  errno = 0;
+
+  EXPECT_FP_EQ(aNaN, __llvm_libc::acosf(aNaN));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ(aNaN, __llvm_libc::acosf(inf));
+  EXPECT_MATH_ERRNO(EDOM);
+
+  EXPECT_FP_EQ(aNaN, __llvm_libc::acosf(neg_inf));
+  EXPECT_MATH_ERRNO(EDOM);
+}
+
+TEST(LlvmLibcAcosfTest, InFloatRange) {
+  constexpr uint32_t COUNT = 1000000;
+  constexpr uint32_t STEP = UINT32_MAX / COUNT;
+  for (uint32_t i = 0, v = 0; i <= COUNT; ++i, v += STEP) {
+    float x = float(FPBits(v));
+    if (isnan(x) || isinf(x))
+      continue;
+    ASSERT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Acos, x,
+                                   __llvm_libc::acosf(x), 0.5);
+  }
+}
+
+TEST(LlvmLibcAcosfTest, SpecificBitPatterns) {
+  constexpr int N = 13;
+  constexpr uint32_t INPUTS[N] = {
+      0x3f000000, // x = 0.5f
+      0x3f3504f3, // x = sqrt(2)/2, FE_DOWNWARD
+      0x3f3504f4, // x = sqrt(2)/2, FE_UPWARD
+      0x3f5db3d7, // x = sqrt(3)/2, FE_DOWNWARD
+      0x3f5db3d8, // x = sqrt(3)/2, FE_UPWARD
+      0x3f800000, // x = 1.0f
+      0x40000000, // x = 2.0f
+      0x328885a3, // x = 0x1.110b46p-26
+      0x39826222, // x = 0x1.04c444p-12
+      0x3d09bf86, // x = 0x1.137f0cp-5f
+      0x3de5fa1e, // x = 0x1.cbf43cp-4f
+      0x3f083a1a, // x = 0x1.107434p-1f
+      0x3f7741b6, // x = 0x1.ee836cp-1f
+  };
+
+  for (int i = 0; i < N; ++i) {
+    float x = float(FPBits(INPUTS[i]));
+    EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Acos, x,
+                                   __llvm_libc::acosf(x), 0.5);
+    EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Acos, -x,
+                                   __llvm_libc::acosf(-x), 0.5);
+  }
+}
diff --git a/libc/test/src/math/exhaustive/CMakeLists.txt b/libc/test/src/math/exhaustive/CMakeLists.txt
@@ -341,3 +341,20 @@ add_fp_unittest(
   LINK_LIBRARIES
     -lpthread
 )
+
+add_fp_unittest(
+  acosf_test
+  NO_RUN_POSTBUILD
+  NEED_MPFR
+  SUITE
+    libc_math_exhaustive_tests
+  SRCS
+    acosf_test.cpp
+  DEPENDS
+    .exhaustive_test
+    libc.include.math
+    libc.src.math.acosf
+    libc.src.__support.FPUtil.fp_bits
+  LINK_LIBRARIES
+    -lpthread
+)
diff --git a/libc/test/src/math/exhaustive/acosf_test.cpp b/libc/test/src/math/exhaustive/acosf_test.cpp
@@ -0,0 +1,76 @@
+//===-- Exhaustive test for acosf -----------------------------------------===//
+//
+// 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/__support/FPUtil/FPBits.h"
+#include "src/math/acosf.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+
+#include <thread>
+
+using FPBits = __llvm_libc::fputil::FPBits<float>;
+
+namespace mpfr = __llvm_libc::testing::mpfr;
+
+struct LlvmLibcAcosfExhaustiveTest : public LlvmLibcExhaustiveTest<uint32_t> {
+  bool check(uint32_t start, uint32_t stop,
+             mpfr::RoundingMode rounding) override {
+    mpfr::ForceRoundingMode r(rounding);
+    uint32_t bits = start;
+    bool result = true;
+    do {
+      FPBits xbits(bits);
+      float x = float(xbits);
+      result &= EXPECT_MPFR_MATCH(mpfr::Operation::Acos, x,
+                                  __llvm_libc::acosf(x), 0.5, rounding);
+    } while (bits++ < stop);
+    return result;
+  }
+};
+
+static const int NUM_THREADS = std::thread::hardware_concurrency();
+
+// Range: [0, Inf];
+static const uint32_t POS_START = 0x0000'0000U;
+static const uint32_t POS_STOP = 0x7f80'0000U;
+
+TEST_F(LlvmLibcAcosfExhaustiveTest, PostiveRangeRoundNearestTieToEven) {
+  test_full_range(POS_START, POS_STOP, mpfr::RoundingMode::Nearest);
+}
+
+TEST_F(LlvmLibcAcosfExhaustiveTest, PostiveRangeRoundUp) {
+  test_full_range(POS_START, POS_STOP, mpfr::RoundingMode::Upward);
+}
+
+TEST_F(LlvmLibcAcosfExhaustiveTest, PostiveRangeRoundDown) {
+  test_full_range(POS_START, POS_STOP, mpfr::RoundingMode::Downward);
+}
+
+TEST_F(LlvmLibcAcosfExhaustiveTest, PostiveRangeRoundTowardZero) {
+  test_full_range(POS_START, POS_STOP, mpfr::RoundingMode::TowardZero);
+}
+
+// Range: [-Inf, 0];
+static const uint32_t NEG_START = 0xb000'0000U;
+static const uint32_t NEG_STOP = 0xff80'0000U;
+
+TEST_F(LlvmLibcAcosfExhaustiveTest, NegativeRangeRoundNearestTieToEven) {
+  test_full_range(NEG_START, NEG_STOP, mpfr::RoundingMode::Nearest);
+}
+
+TEST_F(LlvmLibcAcosfExhaustiveTest, NegativeRangeRoundUp) {
+  test_full_range(NEG_START, NEG_STOP, mpfr::RoundingMode::Upward);
+}
+
+TEST_F(LlvmLibcAcosfExhaustiveTest, NegativeRangeRoundDown) {
+  test_full_range(NEG_START, NEG_STOP, mpfr::RoundingMode::Downward);
+}
+
+TEST_F(LlvmLibcAcosfExhaustiveTest, NegativeRangeRoundTowardZero) {
+  test_full_range(NEG_START, NEG_STOP, mpfr::RoundingMode::TowardZero);
+}
diff --git a/libc/test/src/math/exhaustive/asinf_test.cpp b/libc/test/src/math/exhaustive/asinf_test.cpp
@@ -39,9 +39,8 @@ static const int NUM_THREADS = std::thread::hardware_concurrency();
 // Range: [0, Inf];
 static const uint32_t POS_START = 0x0000'0000U;
 static const uint32_t POS_STOP = 0x7f80'0000U;
-/
 
-    TEST_F(LlvmLibcAsinfExhaustiveTest, PostiveRangeRoundNearestTieToEven) {
+TEST_F(LlvmLibcAsinfExhaustiveTest, PostiveRangeRoundNearestTieToEven) {
   test_full_range(POS_START, POS_STOP, mpfr::RoundingMode::Nearest);
 }
 

diff --git a/libc/utils/MPFRWrapper/MPFRUtils.cpp b/libc/utils/MPFRWrapper/MPFRUtils.cpp
@@ -184,6 +184,12 @@ class MPFRNumber {
     return result;
   }
 
+  MPFRNumber acos() const {
+    MPFRNumber result(*this);
+    mpfr_acos(result.value, value, mpfr_rounding);
+    return result;
+  }
+
   MPFRNumber asin() const {
     MPFRNumber result(*this);
     mpfr_asin(result.value, value, mpfr_rounding);
@@ -526,6 +532,8 @@ unary_operation(Operation op, InputType input, unsigned int precision,
   switch (op) {
   case Operation::Abs:
     return mpfrInput.abs();
+  case Operation::Acos:
+    return mpfrInput.acos();
   case Operation::Asin:
     return mpfrInput.asin();
   case Operation::Atan:

diff --git a/libc/utils/MPFRWrapper/MPFRUtils.h b/libc/utils/MPFRWrapper/MPFRUtils.h
@@ -25,6 +25,7 @@ enum class Operation : int {
   // and output floating point numbers are of the same kind.
   BeginUnaryOperationsSingleOutput,
   Abs,
+  Acos,
   Asin,
   Atan,
   Atanh,
-Original file line number
+Diff line change
@@ Expand Up / @@ -25,6 +25,7 @@ enum class Operation : int { @@
       // and output floating point numbers are of the same kind.
       BeginUnaryOperationsSingleOutput,
       Abs,
+      Acos,
       Asin,
       Atan,
       Atanh,
@@ Expand Down @@