# [libc-commits] [libc] e2f065c - [libc][math] Implement asinf function correctly rounded for all rounding modes.

Tue Ly via libc-commits libc-commits at lists.llvm.org
Wed Sep 7 16:28:03 PDT 2022

```Author: Tue Ly
Date: 2022-09-07T19:27:47-04:00

LOG: [libc][math] Implement asinf function correctly rounded for all rounding modes.

Implement asinf function correctly rounded for all rounding modes.

For `|x| <= 0.5`, we approximate `asin(x)` by
```
asin(x) = x * P(x^2)
```
where `P(X^2) = Q(X)` is a degree-20 minimax even polynomial approximating
`asin(x)/x` on `[0, 0.5]` generated by Sollya with:
```
> Q = fpminimax(asin(x)/x, [|0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20|],
[|1, D...|], [0, 0.5]);
```

When `|x| > 0.5`, we perform range reduction as follow:
Assume further that `0.5 < x <= 1`, and let:
```
y = asin(x)
```
We will use the double angle formula:
```
cos(2X) = 1 - 2 sin^2(X)
```
and the complement angle identity:
```
x = sin(y) = cos(pi/2 - y)
= 1 - 2 sin^2 (pi/4 - y/2)
```
So:
```
sin(pi/4 - y/2) = sqrt( (1 - x)/2 )
```
And hence:
```
pi/4 - y/2 = asin( sqrt( (1 - x)/2 ) )
```
Equivalently:
```
asin(x) = y = pi/2 - 2 * asin( sqrt( (1 - x)/2 ) )
```
Let `u = (1 - x)/2`, then
```
asin(x) = pi/2 - 2 * asin(u)
```
Moreover, since `0.5 < x <= 1`,
```
0 <= u < 1/4, and 0 <= sqrt(u) < 0.5.
```
And hence we can reuse the same polynomial approximation of `asin(x)` when
`|x| <= 0.5`:
```
asin(x) = pi/2 - 2 * u * P(u^2).
```

Performance benchmark using `perf` tool from the CORE-MATH project on Ryzen 1700:
```
\$ CORE_MATH_PERF_MODE="rdtsc" ./perf.sh asinf
CORE-MATH reciprocal throughput   : 23.418
System LIBC reciprocal throughput : 27.310
LIBC reciprocal throughput        : 22.741

\$ CORE_MATH_PERF_MODE="rdtsc" ./perf.sh asinf --latency
GNU libc version: 2.35
GNU libc release: stable
CORE-MATH latency   : 58.884
System LIBC latency : 62.055
LIBC latency        : 62.037
```

Reviewed By: orex, zimmermann6

Differential Revision: https://reviews.llvm.org/D133400

libc/src/math/asinf.h
libc/src/math/generic/asinf.cpp
libc/test/src/math/asinf_test.cpp
libc/test/src/math/exhaustive/asinf_test.cpp

Modified:
libc/config/darwin/arm/entrypoints.txt
libc/config/linux/aarch64/entrypoints.txt
libc/config/linux/x86_64/entrypoints.txt
libc/config/windows/entrypoints.txt
libc/docs/math.rst
libc/spec/stdc.td
libc/src/math/CMakeLists.txt
libc/src/math/generic/CMakeLists.txt
libc/test/src/math/CMakeLists.txt
libc/test/src/math/exhaustive/CMakeLists.txt
libc/utils/MPFRWrapper/MPFRUtils.cpp
libc/utils/MPFRWrapper/MPFRUtils.h

Removed:

################################################################################
diff  --git a/libc/config/darwin/arm/entrypoints.txt b/libc/config/darwin/arm/entrypoints.txt
index 0b5e21984a3f9..433c245e640b5 100644
--- a/libc/config/darwin/arm/entrypoints.txt
+++ b/libc/config/darwin/arm/entrypoints.txt
@@ -105,6 +105,7 @@ set(TARGET_LIBM_ENTRYPOINTS
libc.src.fenv.feupdateenv

# math.h entrypoints
+    libc.src.math.asinf
libc.src.math.atanf
libc.src.math.atanhf
libc.src.math.copysign

diff  --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
index 0e8e8df8326d4..abc6d77397de3 100644
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -149,6 +149,7 @@ set(TARGET_LIBM_ENTRYPOINTS
libc.src.fenv.feupdateenv

# math.h entrypoints
+    libc.src.math.asinf
libc.src.math.atanf
libc.src.math.atanhf
libc.src.math.copysign

diff  --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 80e178aeaa1b5..60ec5f0748509 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -149,6 +149,7 @@ set(TARGET_LIBM_ENTRYPOINTS
libc.src.fenv.feupdateenv

# math.h entrypoints
+    libc.src.math.asinf
libc.src.math.atanf
libc.src.math.atanhf
libc.src.math.copysign

diff  --git a/libc/config/windows/entrypoints.txt b/libc/config/windows/entrypoints.txt
index bf13a5c082c08..a6791813cab2d 100644
--- a/libc/config/windows/entrypoints.txt
+++ b/libc/config/windows/entrypoints.txt
@@ -106,6 +106,7 @@ set(TARGET_LIBM_ENTRYPOINTS
libc.src.fenv.feupdateenv

# math.h entrypoints
+    libc.src.math.asinf
libc.src.math.atanf
libc.src.math.atanhf
libc.src.math.copysign

diff  --git a/libc/docs/math.rst b/libc/docs/math.rst
index 9356f023ed91b..0cbd53329776b 100644
--- a/libc/docs/math.rst
+++ b/libc/docs/math.rst
@@ -118,7 +118,7 @@ Higher Math Functions
============== ================ =============== ======================
acos
acosh
-asin
+asin           |check|
asinh
atan           |check|
atan2
@@ -154,6 +154,7 @@ Accuracy of Higher Math Functions
============== ================ =============== ======================
<Func>         <Func_f> (float) <Func> (double) <Func_l> (long double)
============== ================ =============== ======================
+asin           |check|
atan           |check|
atanh          |check|
cos            |check|          large
@@ -203,6 +204,8 @@ Performance
|              +-----------+-------------------+-----------+-------------------+                                     +------------+-------------------------+--------------+---------------+
|              | LLVM libc | Reference (glibc) | LLVM libc | Reference (glibc) |                                     | CPU        | OS                      | Compiler     | Special flags |
+==============+===========+===================+===========+===================+=====================================+============+=========================+==============+===============+
+| asinf        |        23 |                27 |        62 |                62 | :math:`[-1, 1]`                     | Ryzen 1700 | Ubuntu 22.04 LTS x86_64 | Clang 14.0.0 | FMA           |
++--------------+-----------+-------------------+-----------+-------------------+-------------------------------------+------------+-------------------------+--------------+---------------+
| atanf        |        27 |                29 |        79 |                68 | :math:`[-10, 10]`                   | Ryzen 1700 | Ubuntu 22.04 LTS x86_64 | Clang 14.0.0 | FMA           |
+--------------+-----------+-------------------+-----------+-------------------+-------------------------------------+------------+-------------------------+--------------+---------------+
| atanhf       |        20 |                66 |        71 |               133 | :math:`[-1, 1]`                     | Ryzen 1700 | Ubuntu 22.04 LTS x86_64 | Clang 14.0.0 | FMA           |

diff  --git a/libc/spec/stdc.td b/libc/spec/stdc.td
index d7daa1d26b05c..fdb6beb1cdf02 100644
--- a/libc/spec/stdc.td
+++ b/libc/spec/stdc.td
@@ -480,6 +480,7 @@ def StdC : StandardSpec<"stdc"> {
FunctionSpec<"sinhf", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
FunctionSpec<"tanhf", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,

+          FunctionSpec<"asinf", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
FunctionSpec<"atanf", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,

FunctionSpec<"atanhf", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,

diff  --git a/libc/src/math/CMakeLists.txt b/libc/src/math/CMakeLists.txt
index eeb78d5aa45c1..313ff6a226ec1 100644
--- a/libc/src/math/CMakeLists.txt
+++ b/libc/src/math/CMakeLists.txt
-O3
)

+

diff  --git a/libc/src/math/asinf.h b/libc/src/math/asinf.h
new file mode 100644
index 0000000000000..71821277ef761
--- /dev/null
+++ b/libc/src/math/asinf.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for asinf -------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_MATH_ASINF_H
+#define LLVM_LIBC_SRC_MATH_ASINF_H
+
+namespace __llvm_libc {
+
+float asinf(float x);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_MATH_ASINF_H

diff  --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index 3436c504cf0b2..a946ae4437952 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
libc.include.math
)

+  asinf
+  SRCS
+    asinf.cpp
+  HDRS
+    ../asinf.h
+  DEPENDS
+    libc.src.__support.FPUtil.except_value_utils
+    libc.src.__support.FPUtil.fp_bits
+    libc.src.__support.FPUtil.polyeval
+    libc.src.__support.FPUtil.sqrt
+  COMPILE_OPTIONS
+    -O3
+)
+
atanf
SRCS

diff  --git a/libc/src/math/generic/asinf.cpp b/libc/src/math/generic/asinf.cpp
new file mode 100644
index 0000000000000..262af0fcbd3bc
--- /dev/null
+++ b/libc/src/math/generic/asinf.cpp
@@ -0,0 +1,169 @@
+//===-- Single-precision asin function ------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/math/asinf.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/PolyEval.h"
+#include "src/__support/FPUtil/except_value_utils.h"
+#include "src/__support/FPUtil/sqrt.h"
+
+#include <errno.h>
+
+namespace __llvm_libc {
+
+// PI / 2
+constexpr double M_MATH_PI_2 = 0x1.921fb54442d18p+0;
+
+static constexpr size_t N_EXCEPTS = 2;
+
+// Exceptional values when |x| <= 0.5
+static constexpr fputil::ExceptValues<float, N_EXCEPTS> ASINF_EXCEPTS_LO = {{
+    // (inputs, RZ output, RU offset, RD offset, RN offset)
+    // x = 0x1.137f0cp-5, asinf(x) = 0x1.138c58p-5 (RZ)
+    {0x3d09bf86, 0x3d09c62c, 1, 0, 1},
+    // x = 0x1.cbf43cp-4, asinf(x) = 0x1.cced1cp-4 (RZ)
+    {0x3de5fa1e, 0x3de6768e, 1, 0, 0},
+}};
+
+// Exceptional values when 0.5 < |x| <= 1
+static constexpr fputil::ExceptValues<float, N_EXCEPTS> ASINF_EXCEPTS_HI = {{
+    // (inputs, RZ output, RU offset, RD offset, RN offset)
+    // x = 0x1.107434p-1, asinf(x) = 0x1.1f4b64p-1 (RZ)
+    {0x3f083a1a, 0x3f0fa5b2, 1, 0, 0},
+    // x = 0x1.ee836cp-1, asinf(x) = 0x1.4f0654p0 (RZ)
+    {0x3f7741b6, 0x3fa7832a, 1, 0, 0},
+}};
+
+// > Q = fpminimax(asin(x)/x, [|0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20|],
+//                 [|1, D...|], [0, 0.5]);
+static constexpr double COEFFS[10] = {
+    0x1.5555555540fa1p-3, 0x1.333333512edc2p-4, 0x1.6db6cc1541b31p-5,
+    0x1.f1caff324770ep-6, 0x1.6e43899f5f4f4p-6, 0x1.1f847cf652577p-6,
+    0x1.9b60f47f87146p-7, 0x1.259e2634c494fp-6, -0x1.df946fa875ddp-8,
+    0x1.02311ecf99c28p-5};
+
+LLVM_LIBC_FUNCTION(float, asinf, (float x)) {
+  using FPBits = typename fputil::FPBits<float>;
+  FPBits xbits(x);
+  uint32_t x_uint = xbits.uintval();
+  uint32_t x_abs = xbits.uintval() & 0x7fff'ffffU;
+  constexpr double SIGN[2] = {1.0, -1.0};
+  uint32_t x_sign = x_uint >> 31;
+
+  // |x| <= 0.5-ish
+  if (x_abs < 0x3f04'471dU) {
+    // |x| < 0x1.d12edp-12
+    if (unlikely(x_abs < 0x39e8'9768U)) {
+      // When |x| < 2^-12, the relative error of the approximation asin(x) ~ x
+      // is:
+      //   |asin(x) - x| / |asin(x)| < |x^3| / (6|x|)
+      //                             = x^2 / 6
+      //                             < 2^-25
+      //                             < epsilon(1)/2.
+      // So the correctly rounded values of asin(x) are:
+      //   = x + sign(x)*eps(x) if rounding mode = FE_TOWARDZERO,
+      //                        or (rounding mode = FE_UPWARD and x is
+      //                        negative),
+      //   = x otherwise.
+      // To simplify the rounding decision and make it more efficient, we use
+      //   fma(x, 2^-25, x) instead.
+      // An exhaustive test shows that this formula work correctly for all
+      // rounding modes up to |x| < 0x1.d12edp-12.
+      // Note: to use the formula x + 2^-25*x to decide the correct rounding, we
+      // do need fma(x, 2^-25, x) to prevent underflow caused by 2^-25*x when
+      // |x| < 2^-125. For targets without FMA instructions, we simply use
+      // double for intermediate results as it is more efficient than using an
+      // emulated version of FMA.
+#if defined(LIBC_TARGET_HAS_FMA)
+#else
+      double xd = static_cast<double>(x);
+#endif // LIBC_TARGET_HAS_FMA
+    }
+
+    // Check for exceptional values
+    if (auto r = ASINF_EXCEPTS_LO.lookup_odd(x_abs, x_sign);
+        unlikely(r.has_value()))
+      return r.value();
+
+    // For |x| <= 0.5, we approximate asinf(x) by:
+    //   asin(x) = x * P(x^2)
+    // Where P(X^2) = Q(X) is a degree-20 minimax even polynomial approximating
+    // asin(x)/x on [0, 0.5] generated by Sollya with:
+    // > Q = fpminimax(asin(x)/x, [|0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20|],
+    //                 [|1, D...|], [0, 0.5]);
+    // An exhaustive test shows that this approximation works well up to a
+    // little more than 0.5.
+    double xd = static_cast<double>(x);
+    double xsq = xd * xd;
+    double x4 = xsq * xsq;
+    double r1 = fputil::polyeval(x4, COEFFS[0], COEFFS[2], COEFFS[4], COEFFS[6],
+                                 COEFFS[8]);
+    double r2 = fputil::polyeval(x4, COEFFS[1], COEFFS[3], COEFFS[5], COEFFS[7],
+                                 COEFFS[9]);
+    double r3 = fputil::multiply_add(xsq, r2, r1);
+    double x3 = xd * xsq;
+  }
+
+  // |x| > 1, return NaNs.
+  if (unlikely(x_abs > 0x3f80'0000U)) {
+    if (x_abs <= 0x7f80'0000U) {
+      errno = EDOM;
+      fputil::set_except(FE_INVALID);
+    }
+    return x +
+           FPBits::build_nan(1 << (fputil::MantissaWidth<float>::VALUE - 1));
+  }
+
+  // Check for exceptional values
+  if (auto r = ASINF_EXCEPTS_HI.lookup_odd(x_abs, x_sign);
+      unlikely(r.has_value()))
+    return r.value();
+
+  // When |x| > 0.5, we perform range reduction as follow:
+  // Assume further that 0.5 < x <= 1, and let:
+  //   y = asin(x)
+  // We will use the double angle formula:
+  //   cos(2y) = 1 - 2 sin^2(y)
+  // and the complement angle identity:
+  //   x = sin(y) = cos(pi/2 - y)
+  //              = 1 - 2 sin^2 (pi/4 - y/2)
+  // So:
+  //   sin(pi/4 - y/2) = sqrt( (1 - x)/2 )
+  // And hence:
+  //   pi/4 - y/2 = asin( sqrt( (1 - x)/2 ) )
+  // Equivalently:
+  //   asin(x) = y = pi/2 - 2 * asin( sqrt( (1 - x)/2 ) )
+  // Let u = (1 - x)/2, then
+  //   asin(x) = pi/2 - 2 * asin(u)
+  // Moreover, since 0.5 < x <= 1,
+  //   0 <= u < 1/4, and 0 <= sqrt(u) < 0.5,
+  // And hence we can reuse the same polynomial approximation of asin(x) when
+  // |x| <= 0.5:
+  //   asin(x) = pi/2 - 2 * u * P(u^2),
+
+  xbits.set_sign(false);
+  double xd = static_cast<double>(xbits.get_val());
+  double u = fputil::multiply_add(-0.5, xd, 0.5);
+  double cv = -2 * fputil::sqrt(u);
+
+  double usq = u * u;
+  double r1 = fputil::polyeval(usq, COEFFS[0], COEFFS[2], COEFFS[4], COEFFS[6],
+                               COEFFS[8]);
+  double r2 = fputil::polyeval(usq, COEFFS[1], COEFFS[3], COEFFS[5], COEFFS[7],
+                               COEFFS[9]);
+  double r3 = fputil::multiply_add(u, r2, r1);
+  double r = fputil::multiply_add(cv * u, r3, M_MATH_PI_2 + cv);
+  return SIGN[x_sign] * r;
+}
+
+} // namespace __llvm_libc

diff  --git a/libc/test/src/math/CMakeLists.txt b/libc/test/src/math/CMakeLists.txt
index e69d855c15fa5..b5669057c0509 100644
--- a/libc/test/src/math/CMakeLists.txt
+++ b/libc/test/src/math/CMakeLists.txt
libc.src.__support.FPUtil.fp_bits
)

+  asinf_test
+  NEED_MPFR
+  SUITE
+    libc_math_unittests
+  SRCS
+    asinf_test.cpp
+  DEPENDS
+    libc.include.errno
+    libc.src.errno.errno
+    libc.src.math.asinf
+    libc.src.__support.FPUtil.fp_bits
+)
+
atanf_test
NEED_MPFR

diff  --git a/libc/test/src/math/asinf_test.cpp b/libc/test/src/math/asinf_test.cpp
new file mode 100644
index 0000000000000..93443fc517bce
--- /dev/null
+++ b/libc/test/src/math/asinf_test.cpp
@@ -0,0 +1,80 @@
+//===-- Unittests for asinf
+//------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/math/asinf.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(LlvmLibcAsinfTest, SpecialNumbers) {
+  errno = 0;
+
+  EXPECT_FP_EQ(aNaN, __llvm_libc::asinf(aNaN));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ(0.0f, __llvm_libc::asinf(0.0f));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ(-0.0f, __llvm_libc::asinf(-0.0f));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ(aNaN, __llvm_libc::asinf(inf));
+  EXPECT_MATH_ERRNO(EDOM);
+
+  EXPECT_FP_EQ(aNaN, __llvm_libc::asinf(neg_inf));
+  EXPECT_MATH_ERRNO(EDOM);
+}
+
+TEST(LlvmLibcAsinfTest, 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::Asin, x,
+                                   __llvm_libc::asinf(x), 0.5);
+  }
+}
+
+TEST(LlvmLibcAsinfTest, SpecificBitPatterns) {
+  constexpr int N = 11;
+  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
+      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::Asin, x,
+                                   __llvm_libc::asinf(x), 0.5);
+    EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Asin, -x,
+                                   __llvm_libc::asinf(-x), 0.5);
+  }
+}

diff  --git a/libc/test/src/math/exhaustive/CMakeLists.txt b/libc/test/src/math/exhaustive/CMakeLists.txt
index 5a45e3febe441..1051e87c40192 100644
--- a/libc/test/src/math/exhaustive/CMakeLists.txt
+++ b/libc/test/src/math/exhaustive/CMakeLists.txt
)

+  asinf_test
+  NO_RUN_POSTBUILD
+  NEED_MPFR
+  SUITE
+    libc_math_exhaustive_tests
+  SRCS
+    asinf_test.cpp
+  DEPENDS
+    .exhaustive_test
+    libc.include.math
+    libc.src.math.asinf
+    libc.src.__support.FPUtil.fp_bits
+)

diff  --git a/libc/test/src/math/exhaustive/asinf_test.cpp b/libc/test/src/math/exhaustive/asinf_test.cpp
new file mode 100644
index 0000000000000..fa16acbe27eb2
--- /dev/null
+++ b/libc/test/src/math/exhaustive/asinf_test.cpp
@@ -0,0 +1,78 @@
+//===-- Exhaustive test for asinf -----------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+//
+//===----------------------------------------------------------------------===//
+
+#include "exhaustive_test.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/math/asinf.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+
+
+using FPBits = __llvm_libc::fputil::FPBits<float>;
+
+namespace mpfr = __llvm_libc::testing::mpfr;
+
+struct LlvmLibcAsinfExhaustiveTest : 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::Asin, x,
+                                  __llvm_libc::asinf(x), 0.5, rounding);
+      // if (!result) break;
+    } while (bits++ < stop);
+    return result;
+  }
+};
+
+
+// Range: [0, Inf];
+static const uint32_t POS_START = 0x0000'0000U;
+static const uint32_t POS_STOP = 0x7f80'0000U;
+/
+
+    TEST_F(LlvmLibcAsinfExhaustiveTest, PostiveRangeRoundNearestTieToEven) {
+  test_full_range(POS_START, POS_STOP, mpfr::RoundingMode::Nearest);
+}
+
+TEST_F(LlvmLibcAsinfExhaustiveTest, PostiveRangeRoundUp) {
+  test_full_range(POS_START, POS_STOP, mpfr::RoundingMode::Upward);
+}
+
+TEST_F(LlvmLibcAsinfExhaustiveTest, PostiveRangeRoundDown) {
+  test_full_range(POS_START, POS_STOP, mpfr::RoundingMode::Downward);
+}
+
+TEST_F(LlvmLibcAsinfExhaustiveTest, PostiveRangeRoundTowardZero) {
+  test_full_range(POS_START, POS_STOP, mpfr::RoundingMode::TowardZero);
+}
+
+// Range: [-Inf, 0];
+static const uint32_t NEG_START = 0x8000'0000U;
+static const uint32_t NEG_STOP = 0xff80'0000U;
+
+TEST_F(LlvmLibcAsinfExhaustiveTest, NegativeRangeRoundNearestTieToEven) {
+  test_full_range(NEG_START, NEG_STOP, mpfr::RoundingMode::Nearest);
+}
+
+TEST_F(LlvmLibcAsinfExhaustiveTest, NegativeRangeRoundUp) {
+  test_full_range(NEG_START, NEG_STOP, mpfr::RoundingMode::Upward);
+}
+
+TEST_F(LlvmLibcAsinfExhaustiveTest, NegativeRangeRoundDown) {
+  test_full_range(NEG_START, NEG_STOP, mpfr::RoundingMode::Downward);
+}
+
+TEST_F(LlvmLibcAsinfExhaustiveTest, NegativeRangeRoundTowardZero) {
+  test_full_range(NEG_START, NEG_STOP, mpfr::RoundingMode::TowardZero);
+}

diff  --git a/libc/utils/MPFRWrapper/MPFRUtils.cpp b/libc/utils/MPFRWrapper/MPFRUtils.cpp
index 22d056b699526..910233e87dda7 100644
--- a/libc/utils/MPFRWrapper/MPFRUtils.cpp
+++ b/libc/utils/MPFRWrapper/MPFRUtils.cpp
@@ -176,12 +176,20 @@ class MPFRNumber {
return *this;
}

+  bool is_nan() const { return mpfr_nan_p(value); }
+
MPFRNumber abs() const {
MPFRNumber result(*this);
mpfr_abs(result.value, value, mpfr_rounding);
return result;
}

+  MPFRNumber asin() const {
+    MPFRNumber result(*this);
+    mpfr_asin(result.value, value, mpfr_rounding);
+    return result;
+  }
+
MPFRNumber atan() const {
MPFRNumber result(*this);
mpfr_atan(result.value, value, mpfr_rounding);
@@ -436,6 +444,12 @@ class MPFRNumber {
if (thisAsT == input)
return T(0.0);

+    if (is_nan()) {
+      if (fputil::FPBits<T>(input).is_nan())
+        return T(0.0);
+      return T(fputil::FPBits<T>::inf());
+    }
+
int thisExponent = fputil::FPBits<T>(thisAsT).get_exponent();
int inputExponent = fputil::FPBits<T>(input).get_exponent();
// Adjust the exponents for denormal numbers.
@@ -512,6 +526,8 @@ unary_operation(Operation op, InputType input, unsigned int precision,
switch (op) {
case Operation::Abs:
return mpfrInput.abs();
+  case Operation::Asin:
+    return mpfrInput.asin();
case Operation::Atan:
return mpfrInput.atan();
case Operation::Atanh:

diff  --git a/libc/utils/MPFRWrapper/MPFRUtils.h b/libc/utils/MPFRWrapper/MPFRUtils.h
index f098c29138877..2f9f6f03d6b30 100644
--- 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,
+  Asin,
Atan,
Atanh,
Ceil,

```