[libc-commits] [libc] [libc][math] Implement double-precision asinh (PR #199957)
via libc-commits
libc-commits at lists.llvm.org
Wed May 27 04:06:11 PDT 2026
llvmorg-github-actions[bot] wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libc
Author: Aayush Shrivastava (iamaayushrivastava)
<details>
<summary>Changes</summary>
This PR adds an implementation of the double-precision inverse hyperbolic sine function `asinh` to the `math` library.
---
Full diff: https://github.com/llvm/llvm-project/pull/199957.diff
9 Files Affected:
- (modified) libc/config/linux/x86_64/entrypoints.txt (+1)
- (modified) libc/src/__support/math/CMakeLists.txt (+14)
- (added) libc/src/__support/math/asinh.h (+79)
- (modified) libc/src/math/generic/CMakeLists.txt (+10)
- (added) libc/src/math/generic/asinh.cpp (+16)
- (modified) libc/test/src/math/CMakeLists.txt (+12)
- (added) libc/test/src/math/asinh_test.cpp (+99)
- (modified) libc/test/src/math/smoke/CMakeLists.txt (+11)
- (added) libc/test/src/math/smoke/asinh_test.cpp (+57)
``````````diff
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 5545790fecd85..ee4a8eff8ebf2 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -538,6 +538,7 @@ set(TARGET_LIBM_ENTRYPOINTS
libc.src.math.acospif
libc.src.math.asin
libc.src.math.asinf
+ libc.src.math.asinh
libc.src.math.asinhf
libc.src.math.asinpi
libc.src.math.asinpif
diff --git a/libc/src/__support/math/CMakeLists.txt b/libc/src/__support/math/CMakeLists.txt
index 9e3ec26cdc881..7367bec8ba1a3 100644
--- a/libc/src/__support/math/CMakeLists.txt
+++ b/libc/src/__support/math/CMakeLists.txt
@@ -157,6 +157,20 @@ add_header_library(
libc.src.__support.macros.properties.cpu_features
)
+add_header_library(
+ asinh
+ HDRS
+ asinh.h
+ DEPENDS
+ .log
+ .log1p
+ libc.src.__support.FPUtil.fenv_impl
+ libc.src.__support.FPUtil.fp_bits
+ libc.src.__support.FPUtil.sqrt
+ libc.src.__support.macros.config
+ libc.src.__support.macros.optimization
+)
+
add_header_library(
asinhf
HDRS
diff --git a/libc/src/__support/math/asinh.h b/libc/src/__support/math/asinh.h
new file mode 100644
index 0000000000000..7e2884b80acad
--- /dev/null
+++ b/libc/src/__support/math/asinh.h
@@ -0,0 +1,79 @@
+//===-- Implementation header for asinh -------------------------*- 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___SUPPORT_MATH_ASINH_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_ASINH_H
+
+#include "log.h"
+#include "log1p.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/sqrt.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+LIBC_INLINE double asinh(double x) {
+ using FPBits = fputil::FPBits<double>;
+ FPBits xbits(x);
+
+ // Handle NaN.
+ if (LIBC_UNLIKELY(xbits.is_nan())) {
+ if (xbits.is_signaling_nan()) {
+ fputil::raise_except_if_required(FE_INVALID);
+ return FPBits::quiet_nan().get_val();
+ }
+ return x;
+ }
+
+ // Handle +/-inf: asinh(+/-inf) = +/-inf.
+ if (LIBC_UNLIKELY(xbits.is_inf()))
+ return x;
+
+ uint64_t x_abs_u = xbits.abs().uintval();
+ double x_abs = xbits.abs().get_val();
+ bool is_neg = xbits.is_neg();
+
+ // For very small |x| (|x| <= 2^-26), asinh(x) ~ x.
+ // Use FP arithmetic to ensure FTZ/DAZ mode behavior.
+ if (LIBC_UNLIKELY(x_abs_u <= 0x3e50000000000000ULL)) {
+ // asinh(+/-0) = +/-0, preserve sign of zero exactly.
+ if (LIBC_UNLIKELY(x_abs_u == 0))
+ return x;
+ double x2 = x_abs * x_abs;
+ double result = x_abs - x2 * x_abs * (1.0 / 6.0);
+ return is_neg ? -result : result;
+ }
+
+ double result;
+ // For large |x| (|x| >= 2^28): asinh(x) ~ log(2|x|) = log(|x|) + log(2).
+ if (LIBC_UNLIKELY(x_abs_u >= 0x41b0000000000000ULL)) {
+ constexpr double LOG_2 = 0x1.62e42fefa39efp-1;
+ result = math::log(x_abs) + LOG_2;
+ } else if (x_abs_u >= 0x3fe0000000000000ULL) {
+ // |x| >= 0.5: asinh(x) = log(x + sqrt(x^2 + 1)).
+ result = math::log(x_abs + fputil::sqrt<double>(x_abs * x_abs + 1.0));
+ } else {
+ // |x| < 0.5: use log1p for better accuracy near 0.
+ // asinh(x) = log1p(x + x^2 / (1 + sqrt(1 + x^2)))
+ double x2 = x_abs * x_abs;
+ double sqrt1px2 = fputil::sqrt<double>(1.0 + x2);
+ result = math::log1p(x_abs + x2 / (1.0 + sqrt1px2));
+ }
+
+ return is_neg ? -result : result;
+}
+
+} // namespace math
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_MATH_ASINH_H
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index 7ccbddba07b8d..955bfa660e05e 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -3722,6 +3722,16 @@ add_entrypoint_object(
libc.src.__support.math.acospif
)
+add_entrypoint_object(
+ asinh
+ SRCS
+ asinh.cpp
+ HDRS
+ ../asinh.h
+ DEPENDS
+ libc.src.__support.math.asinh
+)
+
add_entrypoint_object(
asinhf
SRCS
diff --git a/libc/src/math/generic/asinh.cpp b/libc/src/math/generic/asinh.cpp
new file mode 100644
index 0000000000000..f246cd9497617
--- /dev/null
+++ b/libc/src/math/generic/asinh.cpp
@@ -0,0 +1,16 @@
+//===-- Double-precision asinh implementation -----------------------------===//
+//
+// 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/asinh.h"
+#include "src/__support/math/asinh.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(double, asinh, (double x)) { return math::asinh(x); }
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/test/src/math/CMakeLists.txt b/libc/test/src/math/CMakeLists.txt
index 4213c11eca515..f3d8ecee00cad 100644
--- a/libc/test/src/math/CMakeLists.txt
+++ b/libc/test/src/math/CMakeLists.txt
@@ -2441,6 +2441,18 @@ add_fp_unittest(
libc.src.stdlib.srand
)
+add_fp_unittest(
+ asinh_test
+ NEED_MPFR
+ SUITE
+ libc-math-unittests
+ SRCS
+ asinh_test.cpp
+ DEPENDS
+ libc.src.math.asinh
+ libc.src.__support.FPUtil.fp_bits
+)
+
add_fp_unittest(
asinhf_test
NEED_MPFR
diff --git a/libc/test/src/math/asinh_test.cpp b/libc/test/src/math/asinh_test.cpp
new file mode 100644
index 0000000000000..97a075ff83357
--- /dev/null
+++ b/libc/test/src/math/asinh_test.cpp
@@ -0,0 +1,99 @@
+//===-- Unittests for asinh -----------------------------------------------===//
+//
+// 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/asinh.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+
+using LlvmLibcAsinhTest = LIBC_NAMESPACE::testing::FPTest<double>;
+
+namespace mpfr = LIBC_NAMESPACE::testing::mpfr;
+
+using LIBC_NAMESPACE::testing::tlog;
+
+TEST_F(LlvmLibcAsinhTest, InDoubleRange) {
+ // asinh is odd; test positive range [2^-26, 2^52] and negate for negatives.
+ constexpr uint64_t COUNT = 123'451;
+ uint64_t START = FPBits(0x1.0p-26).uintval();
+ uint64_t STOP = FPBits(0x1.0p52).uintval();
+ uint64_t STEP = (STOP - START) / COUNT;
+
+ auto test = [&](mpfr::RoundingMode rounding_mode) {
+ mpfr::ForceRoundingMode __r(rounding_mode);
+ if (!__r.success)
+ return;
+
+ uint64_t fails = 0;
+ uint64_t count = 0;
+ uint64_t cc = 0;
+ double mx = 0.0, mr = 0.0;
+ double tol = 0.5;
+
+ for (uint64_t i = 0, v = START; i <= COUNT; ++i, v += STEP) {
+ double x = FPBits(v).get_val();
+ if (FPBits(v).is_inf_or_nan())
+ continue;
+
+ // Test positive x.
+ double result = LIBC_NAMESPACE::asinh(x);
+ ++cc;
+ ++count;
+ if (!TEST_MPFR_MATCH_ROUNDING_SILENTLY(mpfr::Operation::Asinh, x, result,
+ 0.5, rounding_mode)) {
+ ++fails;
+ while (!TEST_MPFR_MATCH_ROUNDING_SILENTLY(mpfr::Operation::Asinh, x,
+ result, tol, rounding_mode)) {
+ mx = x;
+ mr = result;
+ if (tol > 1000.0)
+ break;
+ tol *= 2.0;
+ }
+ }
+
+ // Test negative x (asinh is odd).
+ double neg_x = -x;
+ double neg_result = LIBC_NAMESPACE::asinh(neg_x);
+ ++cc;
+ ++count;
+ if (!TEST_MPFR_MATCH_ROUNDING_SILENTLY(mpfr::Operation::Asinh, neg_x,
+ neg_result, 0.5, rounding_mode)) {
+ ++fails;
+ while (!TEST_MPFR_MATCH_ROUNDING_SILENTLY(mpfr::Operation::Asinh,
+ neg_x, neg_result, tol,
+ rounding_mode)) {
+ mx = neg_x;
+ mr = neg_result;
+ if (tol > 1000.0)
+ break;
+ tol *= 2.0;
+ }
+ }
+ }
+ if (fails) {
+ tlog << " Asinh failed: " << fails << "/" << count << "/" << cc
+ << " tests.\n";
+ tlog << " Max ULPs is at most: " << static_cast<uint64_t>(tol) << ".\n";
+ EXPECT_MPFR_MATCH(mpfr::Operation::Asinh, mx, mr, 0.5, rounding_mode);
+ }
+ };
+
+ tlog << " Test Rounding To Nearest...\n";
+ test(mpfr::RoundingMode::Nearest);
+
+ tlog << " Test Rounding Downward...\n";
+ test(mpfr::RoundingMode::Downward);
+
+ tlog << " Test Rounding Upward...\n";
+ test(mpfr::RoundingMode::Upward);
+
+ tlog << " Test Rounding Toward Zero...\n";
+ test(mpfr::RoundingMode::TowardZero);
+}
diff --git a/libc/test/src/math/smoke/CMakeLists.txt b/libc/test/src/math/smoke/CMakeLists.txt
index 28b85b1a25bbd..f6036a50f0301 100644
--- a/libc/test/src/math/smoke/CMakeLists.txt
+++ b/libc/test/src/math/smoke/CMakeLists.txt
@@ -4734,6 +4734,17 @@ add_fp_unittest(
libc.src.math.atanpif16
)
+add_fp_unittest(
+ asinh_test
+ SUITE
+ libc-math-smoke-tests
+ SRCS
+ asinh_test.cpp
+ DEPENDS
+ libc.src.math.asinh
+ libc.src.__support.FPUtil.fp_bits
+)
+
add_fp_unittest(
asinhf_test
SUITE
diff --git a/libc/test/src/math/smoke/asinh_test.cpp b/libc/test/src/math/smoke/asinh_test.cpp
new file mode 100644
index 0000000000000..97cc84e6f79f4
--- /dev/null
+++ b/libc/test/src/math/smoke/asinh_test.cpp
@@ -0,0 +1,57 @@
+//===-- Unittests for asinh -----------------------------------------------===//
+//
+// 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 "hdr/math_macros.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/math/asinh.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+
+using LlvmLibcAsinhTest = LIBC_NAMESPACE::testing::FPTest<double>;
+
+TEST_F(LlvmLibcAsinhTest, SpecialNumbers) {
+ EXPECT_FP_EQ_WITH_EXCEPTION(aNaN, LIBC_NAMESPACE::asinh(sNaN), FE_INVALID);
+
+ EXPECT_FP_EQ_ALL_ROUNDING(aNaN, LIBC_NAMESPACE::asinh(aNaN));
+
+ EXPECT_FP_EQ_ALL_ROUNDING(inf, LIBC_NAMESPACE::asinh(inf));
+ EXPECT_FP_EQ_ALL_ROUNDING(neg_inf, LIBC_NAMESPACE::asinh(neg_inf));
+
+ EXPECT_FP_EQ_ALL_ROUNDING(0.0, LIBC_NAMESPACE::asinh(0.0));
+ EXPECT_FP_EQ_ALL_ROUNDING(neg_zero, LIBC_NAMESPACE::asinh(neg_zero));
+}
+
+#ifdef LIBC_TEST_FTZ_DAZ
+
+using namespace LIBC_NAMESPACE::testing;
+
+TEST_F(LlvmLibcAsinhTest, FTZMode) {
+ ModifyMXCSR mxcsr(FTZ);
+
+ const double neg_min_denormal = FPBits::min_subnormal(Sign::NEG).get_val();
+ EXPECT_FP_EQ(0.0, LIBC_NAMESPACE::asinh(min_denormal));
+ EXPECT_FP_EQ(neg_zero, LIBC_NAMESPACE::asinh(neg_min_denormal));
+}
+
+TEST_F(LlvmLibcAsinhTest, DAZMode) {
+ ModifyMXCSR mxcsr(DAZ);
+
+ const double neg_min_denormal = FPBits::min_subnormal(Sign::NEG).get_val();
+ EXPECT_FP_EQ(0.0, LIBC_NAMESPACE::asinh(min_denormal));
+ EXPECT_FP_EQ(neg_zero, LIBC_NAMESPACE::asinh(neg_min_denormal));
+}
+
+TEST_F(LlvmLibcAsinhTest, FTZDAZMode) {
+ ModifyMXCSR mxcsr(FTZ | DAZ);
+
+ const double neg_min_denormal = FPBits::min_subnormal(Sign::NEG).get_val();
+ EXPECT_FP_EQ(0.0, LIBC_NAMESPACE::asinh(min_denormal));
+ EXPECT_FP_EQ(neg_zero, LIBC_NAMESPACE::asinh(neg_min_denormal));
+}
+
+#endif
``````````
</details>
https://github.com/llvm/llvm-project/pull/199957
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