[libc][math][c23] Add acoshf16 C23 math function.

libc/config/linux/aarch64/entrypoints.txt

@@ -644,6 +644,7 @@ endif()
 if(LIBC_TYPES_HAS_FLOAT16)
   list(APPEND TARGET_LIBM_ENTRYPOINTS
     # math.h C23 _Float16 entrypoints
+    libc.src.math.acoshf16
     libc.src.math.canonicalizef16
     libc.src.math.ceilf16
     libc.src.math.copysignf16

libc/config/linux/x86_64/entrypoints.txt

@@ -653,6 +653,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
     # math.h C23 _Float16 entrypoints
     libc.src.math.asinf16
     libc.src.math.acosf16
+    libc.src.math.acoshf16
     libc.src.math.canonicalizef16
     libc.src.math.ceilf16
     libc.src.math.copysignf16

libc/docs/headers/math/index.rst

@@ -251,7 +251,7 @@ Higher Math Functions
 +===========+==================+=================+========================+======================+========================+========================+============================+
 | acos      | |check|          |                 |                        | |check|              |                        | 7.12.4.1               | F.10.1.1                   |
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
-| acosh     | |check|          |                 |                        |                      |                        | 7.12.5.1               | F.10.2.1                   |
+| acosh     | |check|          |                 |                        | |check|              |                        | 7.12.5.1               | F.10.2.1                   |
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
 | acospi    |                  |                 |                        |                      |                        | 7.12.4.8               | F.10.1.8                   |
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+

libc/include/math.yaml

@@ -27,6 +27,13 @@ functions:
     return_type: float
     arguments:
       - type: float
+    name: acoshf16
+    standards:
+      - stdc
+    return_type: _Float16
+    arguments:
+      - type: _Float16
+    guard: LIBC_TYPES_HAS_FLOAT16
   - name: asin
     standards:
       - stdc

libc/src/math/CMakeLists.txt

@@ -46,6 +46,7 @@ add_math_entrypoint_object(acosf16)
 
 add_math_entrypoint_object(acosh)
 add_math_entrypoint_object(acoshf)
+add_math_entrypoint_object(acoshf16)
 
 add_math_entrypoint_object(asin)
 add_math_entrypoint_object(asinf)

libc/src/math/acoshf16.h

@@ -0,0 +1,21 @@
+//===-- Implementation header for acoshf16 ----------------------*- 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_ACOSHF16_H
+#define LLVM_LIBC_SRC_MATH_ACOSHF16_H
+
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/properties/types.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+float16 acoshf16(float16 x);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_MATH_ACOSHF16_H

libc/src/math/generic/CMakeLists.txt

@@ -3944,6 +3944,27 @@ add_entrypoint_object(
     libc.src.__support.macros.optimization
 )
 
+add_entrypoint_object(
+  acoshf16
+  SRCS
+    acoshf16.cpp
+  HDRS
+    ../acoshf16.h
+  DEPENDS
+    .explogxf
+    libc.hdr.errno_macros
+    libc.hdr.fenv_macros
+    libc.src.__support.FPUtil.cast
+    libc.src.__support.FPUtil.except_value_utils
+    libc.src.__support.FPUtil.fenv_impl
+    libc.src.__support.FPUtil.fp_bits
+    libc.src.__support.FPUtil.multiply_add
+    libc.src.__support.FPUtil.polyeval
+    libc.src.__support.FPUtil.sqrt
+    libc.src.__support.macros.optimization
+    libc.src.__support.macros.properties.types 
+)
+
 add_entrypoint_object(
   asinhf
   SRCS

libc/src/math/generic/acoshf16.cpp

@@ -0,0 +1,110 @@
+//===-- Half-precision acosh(x) 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/acoshf16.h"
+#include "explogxf.h"
+#include "hdr/errno_macros.h"
+#include "hdr/fenv_macros.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/PolyEval.h"
+#include "src/__support/FPUtil/cast.h"
+#include "src/__support/FPUtil/except_value_utils.h"
+#include "src/__support/FPUtil/multiply_add.h"
+#include "src/__support/FPUtil/sqrt.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+static constexpr size_t N_EXCEPTS = 2;
+static constexpr fputil::ExceptValues<float16, N_EXCEPTS> ACOSHF16_EXCEPTS{{
+    // (input, RZ output, RU offset, RD offset, RN offset)
+    // x = 0x1.6dcp+1, acoshf16(x) = 0x1.b6p+0 (RZ)
+    {0x41B7, 0x3ED8, 1, 0, 0},
+    // x = 0x1.39p+0, acoshf16(x) = 0x1.4f8p-1 (RZ)
+    {0x3CE4, 0x393E, 1, 0, 1},
+}};
+
+LLVM_LIBC_FUNCTION(float16, acoshf16, (float16 x)) {
+  using FPBits = fputil::FPBits<float16>;
+  FPBits xbits(x);
+  uint16_t x_u = xbits.uintval();
+
+  // Check for NaN input first.
+  if (LIBC_UNLIKELY(xbits.is_inf_or_nan())) {
+    if (xbits.is_signaling_nan()) {
+      fputil::raise_except_if_required(FE_INVALID);
+      return FPBits::quiet_nan().get_val();
+    }
+    if (xbits.is_neg()) {
+      fputil::set_errno_if_required(EDOM);
+      fputil::raise_except_if_required(FE_INVALID);
+      return FPBits::quiet_nan().get_val();
+    }
+    return x;
+  }
+
+  // Domain error for inputs less than 1.0.
+  if (LIBC_UNLIKELY(x <= 1.0f)) {
+    if (x == 1.0f)
+      return FPBits::zero().get_val();
+    fputil::set_errno_if_required(EDOM);
+    fputil::raise_except_if_required(FE_INVALID);
+    return FPBits::quiet_nan().get_val();
+  }
+
+  if (auto r = ACOSHF16_EXCEPTS.lookup(xbits.uintval());
+      LIBC_UNLIKELY(r.has_value()))
+    return r.value();
+
+  float xf = x;
+  // High-precision polynomial approximation for inputs close to 1.0
+  // ([1, 1.25)).
+  //
+  // Brief derivation:
+  // 1. Expand acosh(1 + delta) using Taylor series around delta=0:
+  //    acosh(1 + delta) ≈ sqrt(2 * delta) * [1 - delta/12 + 3*delta^2/160
+  //                     - 5*delta^3/896 + 35*delta^4/18432 + ...]
+  // 2. Truncate the series to fit accurately for delta in [0, 0.25].
+  // 3. Polynomial coefficients (from sollya) used here are:
+  //    P(delta) ≈ 1 - 0x1.555556p-4 * delta + 0x1.333334p-6 * delta^2
+  //               - 0x1.6db6dcp-8 * delta^3 + 0x1.f1c71cp-10 * delta^4
+  // 4. The Sollya commands used to generate these coefficients were:
+  //      > display = hexadecimal;
+  //      > round(1/12, SG, RN);
+  //      > round(3/160, SG, RN);
+  //      > round(5/896, SG, RN);
+  //      > round(35/18432, SG, RN);
+  //      With hexadecimal display mode enabled, the outputs were:
+  //      0x1.555556p-4
+  //      0x1.333334p-6
+  //      0x1.6db6dcp-8
+  //      0x1.f1c71cp-10
+  // 5. The maximum absolute error, estimated using:
+  //      dirtyinfnorm(acosh(1 + x) - sqrt(2*x) * P(x), [0, 0.25])
+  //    is:
+  //      0x1.d84281p-22
+  if (LIBC_UNLIKELY(x_u < 0x3D00U)) {
+    float delta = xf - 1.0f;
+    float sqrt_2_delta = fputil::sqrt<float>(2.0 * delta);
+    float pe = fputil::polyeval(delta, 0x1p+0f, -0x1.555556p-4f, 0x1.333334p-6f,
+                                -0x1.6db6dcp-8f, 0x1.f1c71cp-10f);
+    float approx = sqrt_2_delta * pe;
+    return fputil::cast<float16>(approx);
+  }
+
+  // acosh(x) = log(x + sqrt(x^2 - 1))
+  float sqrt_term = fputil::sqrt<float>(fputil::multiply_add(xf, xf, -1.0f));
+  float result = static_cast<float>(log_eval(xf + sqrt_term));
+
+  return fputil::cast<float16>(result);
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/test/src/math/CMakeLists.txt

@@ -2173,6 +2173,17 @@ add_fp_unittest(
     libc.src.__support.FPUtil.fp_bits
 )
 
+add_fp_unittest(
+  acoshf16_test
+  NEED_MPFR
+  SUITE
+    libc-math-unittests
+  SRCS
+    acoshf16_test.cpp
+  DEPENDS
+    libc.src.math.acoshf16
+)
+
 add_fp_unittest(
   asinf_test
   NEED_MPFR

libc/test/src/math/acoshf16_test.cpp

@@ -0,0 +1,28 @@
+//===-- Unittests for acoshf16 --------------------------------------------===//
+//
+// 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/acoshf16.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+#include <stdint.h>
+
+using LlvmLibcAcoshf16Test = LIBC_NAMESPACE::testing::FPTest<float16>;
+namespace mpfr = LIBC_NAMESPACE::testing::mpfr;
+
+static constexpr uint16_t START = 0x3c00U;
+static constexpr uint16_t STOP = 0x7c00;
+
+TEST_F(LlvmLibcAcoshf16Test, PositiveRange) {
+  for (uint16_t v = START; v <= STOP; ++v) {
+    float16 x = FPBits(v).get_val();
+    EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Acosh, x,
+                                   LIBC_NAMESPACE::acoshf16(x), 0.5);
+  }
+}

libc/test/src/math/smoke/CMakeLists.txt

@@ -3945,6 +3945,18 @@ add_fp_unittest(
     libc.src.__support.FPUtil.fp_bits
 )
 
+add_fp_unittest(
+  acoshf16_test
+  SUITE
+    libc-math-smoke-tests
+  SRCS
+    acoshf16_test.cpp
+  DEPENDS
+    libc.src.errno.errno
+    libc.src.math.acoshf16
+    libc.src.__support.FPUtil.cast
+)
+
 add_fp_unittest(
   asinf_test
   SUITE

libc/test/src/math/smoke/acoshf16_test.cpp

@@ -0,0 +1,70 @@
+//===-- Unittests for acoshf16 --------------------------------------------===//
+//
+// 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/cast.h"
+#include "src/errno/libc_errno.h"
+#include "src/math/acoshf16.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+
+using LlvmLibcAcoshf16Test = LIBC_NAMESPACE::testing::FPTest<float16>;
+
+TEST_F(LlvmLibcAcoshf16Test, SpecialNumbers) {
+  LIBC_NAMESPACE::libc_errno = 0;
+  EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::acoshf16(aNaN));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ_WITH_EXCEPTION(aNaN, LIBC_NAMESPACE::acoshf16(sNaN), FE_INVALID);
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ_WITH_EXCEPTION(aNaN, LIBC_NAMESPACE::acoshf16(zero), FE_INVALID);
+  EXPECT_MATH_ERRNO(EDOM);
+
+  EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::acoshf16(neg_zero));
+  EXPECT_MATH_ERRNO(EDOM);
+
+  EXPECT_FP_EQ_WITH_EXCEPTION(aNaN, LIBC_NAMESPACE::acoshf16(neg_zero),
+                              FE_INVALID);
+  EXPECT_MATH_ERRNO(EDOM);
+
+  EXPECT_FP_EQ(inf, LIBC_NAMESPACE::acoshf16(inf));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::acoshf16(neg_inf));
+  EXPECT_MATH_ERRNO(EDOM);
+
+  EXPECT_FP_EQ_WITH_EXCEPTION(aNaN, LIBC_NAMESPACE::acoshf16(neg_inf),
+                              FE_INVALID);
+  EXPECT_MATH_ERRNO(EDOM);
+
+  EXPECT_FP_EQ(zero, LIBC_NAMESPACE::acoshf16(
+                         LIBC_NAMESPACE::fputil::cast<float16>(1.0)));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::acoshf16(
+                         LIBC_NAMESPACE::fputil::cast<float16>(0.5)));
+  EXPECT_MATH_ERRNO(EDOM);
+
+  EXPECT_FP_EQ_WITH_EXCEPTION(
+      aNaN,
+      LIBC_NAMESPACE::acoshf16(LIBC_NAMESPACE::fputil::cast<float16>(-1.0)),
+      FE_INVALID);
+  EXPECT_MATH_ERRNO(EDOM);
+
+  EXPECT_FP_EQ_WITH_EXCEPTION(
+      aNaN,
+      LIBC_NAMESPACE::acoshf16(LIBC_NAMESPACE::fputil::cast<float16>(-2.0)),
+      FE_INVALID);
+  EXPECT_MATH_ERRNO(EDOM);
+
+  EXPECT_FP_EQ_WITH_EXCEPTION(
+      aNaN,
+      LIBC_NAMESPACE::acoshf16(LIBC_NAMESPACE::fputil::cast<float16>(-3.0)),
+      FE_INVALID);
+  EXPECT_MATH_ERRNO(EDOM);
+}