[libc-commits] [libc] [llvm] [libc][math] Refactor atanpif16 to Header Only. (PR #179158)
Brady Bangasser via libc-commits
libc-commits at lists.llvm.org
Sun Feb 1 19:59:40 PST 2026
https://github.com/BradyBangasser created https://github.com/llvm/llvm-project/pull/179158
Refactored atanpif16 function to be constexpr and header only, #178105
>From 753c7cdb9e75d159df17f71250c9ae898324f40f Mon Sep 17 00:00:00 2001
From: Brady Bangasser <bradybbangasser at gmail.com>
Date: Sun, 1 Feb 2026 21:35:12 -0600
Subject: [PATCH] [libc][math] Refactor atanpif16 to Header Only.
---
libc/shared/math.h | 1 +
libc/shared/math/atanpif16.h | 29 +++++
libc/src/__support/math/CMakeLists.txt | 15 +++
libc/src/__support/math/atanpif16.h | 115 ++++++++++++++++++
libc/src/math/generic/CMakeLists.txt | 11 +-
libc/src/math/generic/atanpif16.cpp | 95 +--------------
libc/test/shared/CMakeLists.txt | 1 +
libc/test/shared/shared_math_test.cpp | 1 +
.../llvm-project-overlay/libc/BUILD.bazel | 21 ++++
9 files changed, 186 insertions(+), 103 deletions(-)
create mode 100644 libc/shared/math/atanpif16.h
create mode 100644 libc/src/__support/math/atanpif16.h
diff --git a/libc/shared/math.h b/libc/shared/math.h
index b58d29d1ee480..35963dea8df24 100644
--- a/libc/shared/math.h
+++ b/libc/shared/math.h
@@ -30,6 +30,7 @@
#include "math/atanf16.h"
#include "math/atanhf.h"
#include "math/atanhf16.h"
+#include "math/atanpif16.h"
#include "math/cbrt.h"
#include "math/cbrtf.h"
#include "math/cos.h"
diff --git a/libc/shared/math/atanpif16.h b/libc/shared/math/atanpif16.h
new file mode 100644
index 0000000000000..11dcba1e0e406
--- /dev/null
+++ b/libc/shared/math/atanpif16.h
@@ -0,0 +1,29 @@
+
+//===-- Shared atanhif16 function --------------------------------*-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_SHARED_MATH_ATANHF16_H
+#define LLVM_LIBC_SHARED_MATH_ATANHF16_H
+
+#include "shared/libc_common.h"
+
+#ifdef LIBC_TYPES_HAS_FLOAT16
+
+#include "src/__support/math/atanhif16.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace shared {
+
+using math::atanhif16;
+
+} // namespace shared
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_TYPES_HAS_FLOAT16
+
+#endif // LLVM_LIBC_SHARED_MATH_ATANHF16_H
diff --git a/libc/src/__support/math/CMakeLists.txt b/libc/src/__support/math/CMakeLists.txt
index 58e4040911f8e..de5f92bb3dd66 100644
--- a/libc/src/__support/math/CMakeLists.txt
+++ b/libc/src/__support/math/CMakeLists.txt
@@ -302,6 +302,21 @@ add_header_library(
libc.src.__support.macros.optimization
)
+add_header_library(
+ atanhif16
+ HDRS
+ atanhif16.h
+ DEPENDS
+ libc.src.__support.FPUtil.fenv_impl
+ libc.src.__support.FPUtil.fp_bits
+ libc.src.__support.FPUtil.polyeval
+ libc.src.__support.FPUtil.cast
+ libc.src.__support.FPUtil.except_value_utils
+ libc.src.__support.FPUtil.multiply_add
+ libc.src.__support.macros.config
+ libc.src.__support.macros.optimization
+)
+
add_header_library(
asinf
HDRS
diff --git a/libc/src/__support/math/atanpif16.h b/libc/src/__support/math/atanpif16.h
new file mode 100644
index 0000000000000..2a4caf4f72581
--- /dev/null
+++ b/libc/src/__support/math/atanpif16.h
@@ -0,0 +1,115 @@
+//===-- Implementation header for atanpif16 ---------------------*- 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_ATANHIF16_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_ATANHIF16_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/multiply_add.h"
+#include "src/__support/FPUtil/sqrt.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h"
+#include "src/__support/macros/properties/types.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace math {
+
+LIBC_INLINE constexpr float16 atanpif16(float16 x) {
+ using FPBits = fputil::FPBits<float16>;
+
+ FPBits xbits(x);
+ bool is_neg = xbits.is_neg();
+
+ auto signed_result = [is_neg](double r) -> float16 {
+ return fputil::cast<float16>(is_neg ? -r : r);
+ };
+
+ if (LIBC_UNLIKELY(xbits.is_inf_or_nan())) {
+ if (xbits.is_nan()) {
+ if (xbits.is_signaling_nan()) {
+ fputil::raise_except_if_required(FE_INVALID);
+ return FPBits::quiet_nan().get_val();
+ }
+ return x;
+ }
+ // atanpi(±∞) = ±0.5
+ return signed_result(0.5);
+ }
+
+ if (LIBC_UNLIKELY(xbits.is_zero()))
+ return x;
+
+ double x_abs = fputil::cast<double>(xbits.abs().get_val());
+
+ if (LIBC_UNLIKELY(x_abs == 1.0))
+ return signed_result(0.25);
+
+ // evaluate atan(x)/pi using polynomial approximation, valid for |x| <= 0.5
+ constexpr auto atanpi_eval = [](double x) -> double {
+ // polynomial coefficients for atan(x)/pi taylor series
+ // generated using sympy: series(atan(x)/pi, x, 0, 17)
+ constexpr static double POLY_COEFFS[] = {
+ 0x1.45f306dc9c889p-2, // x^1: 1/pi
+ -0x1.b2995e7b7b60bp-4, // x^3: -1/(3*pi)
+ 0x1.04c26be3b06ccp-4, // x^5: 1/(5*pi)
+ -0x1.7483758e69c08p-5, // x^7: -1/(7*pi)
+ 0x1.21bb945252403p-5, // x^9: 1/(9*pi)
+ -0x1.da1bace3cc68ep-6, // x^11: -1/(11*pi)
+ 0x1.912b1c2336cf2p-6, // x^13: 1/(13*pi)
+ -0x1.5bade52f95e7p-6, // x^15: -1/(15*pi)
+ };
+ double x_sq = x * x;
+ return x * fputil::polyeval(x_sq, POLY_COEFFS[0], POLY_COEFFS[1],
+ POLY_COEFFS[2], POLY_COEFFS[3], POLY_COEFFS[4],
+ POLY_COEFFS[5], POLY_COEFFS[6], POLY_COEFFS[7]);
+ };
+
+ // Case 1: |x| <= 0.5 - Direct polynomial evaluation
+ if (LIBC_LIKELY(x_abs <= 0.5)) {
+ double result = atanpi_eval(x_abs);
+ return signed_result(result);
+ }
+
+ // case 2: 0.5 < |x| <= 1 - use double-angle reduction
+ // atan(x) = 2 * atan(x / (1 + sqrt(1 + x^2)))
+ // so atanpi(x) = 2 * atanpi(x') where x' = x / (1 + sqrt(1 + x^2))
+ if (x_abs <= 1.0) {
+ double x_abs_sq = x_abs * x_abs;
+ double sqrt_term = fputil::sqrt<double>(1.0 + x_abs_sq);
+ double x_prime = x_abs / (1.0 + sqrt_term);
+ double result = 2.0 * atanpi_eval(x_prime);
+ return signed_result(result);
+ }
+
+ // case 3: |x| > 1 - use reciprocal transformation
+ // atan(x) = pi/2 - atan(1/x) for x > 0
+ // so atanpi(x) = 1/2 - atanpi(1/x)
+ double x_recip = 1.0 / x_abs;
+ double result = 0.0;
+
+ // if 1/|x| > 0.5, we need to apply Case 2 transformation to 1/|x|
+ if (x_recip > 0.5) {
+ double x_recip_sq = x_recip * x_recip;
+ double sqrt_term = fputil::sqrt<double>(1.0 + x_recip_sq);
+ double x_prime = x_recip / (1.0 + sqrt_term);
+ result = fputil::multiply_add(-2.0, atanpi_eval(x_prime), 0.5);
+ } else {
+ // direct evaluation since 1/|x| <= 0.5
+ result = 0.5 - atanpi_eval(x_recip);
+ }
+
+ return signed_result(result);
+}
+
+} // namespace math
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index 1b18388ed60f8..669c840bef436 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -4232,16 +4232,7 @@ add_entrypoint_object(
HDRS
../atanpif16.h
DEPENDS
- libc.hdr.errno_macros
- libc.hdr.fenv_macros
- libc.src.__support.FPUtil.cast
- 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
+ libc.src.__support.math.atanpif16
)
add_entrypoint_object(
diff --git a/libc/src/math/generic/atanpif16.cpp b/libc/src/math/generic/atanpif16.cpp
index c54087c7165fe..c0e2d1c65059b 100644
--- a/libc/src/math/generic/atanpif16.cpp
+++ b/libc/src/math/generic/atanpif16.cpp
@@ -7,15 +7,7 @@
//===----------------------------------------------------------------------===//
#include "src/math/atanpif16.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/multiply_add.h"
-#include "src/__support/FPUtil/sqrt.h"
-#include "src/__support/macros/optimization.h"
+#include "src/__support/math/atanpif16.h"
namespace LIBC_NAMESPACE_DECL {
@@ -68,90 +60,7 @@ namespace LIBC_NAMESPACE_DECL {
// from Case 2 must be applied recursively to 1/|x|.
LLVM_LIBC_FUNCTION(float16, atanpif16, (float16 x)) {
- using FPBits = fputil::FPBits<float16>;
-
- FPBits xbits(x);
- bool is_neg = xbits.is_neg();
-
- auto signed_result = [is_neg](double r) -> float16 {
- return fputil::cast<float16>(is_neg ? -r : r);
- };
-
- if (LIBC_UNLIKELY(xbits.is_inf_or_nan())) {
- if (xbits.is_nan()) {
- if (xbits.is_signaling_nan()) {
- fputil::raise_except_if_required(FE_INVALID);
- return FPBits::quiet_nan().get_val();
- }
- return x;
- }
- // atanpi(±∞) = ±0.5
- return signed_result(0.5);
- }
-
- if (LIBC_UNLIKELY(xbits.is_zero()))
- return x;
-
- double x_abs = fputil::cast<double>(xbits.abs().get_val());
-
- if (LIBC_UNLIKELY(x_abs == 1.0))
- return signed_result(0.25);
-
- // evaluate atan(x)/pi using polynomial approximation, valid for |x| <= 0.5
- constexpr auto atanpi_eval = [](double x) -> double {
- // polynomial coefficients for atan(x)/pi taylor series
- // generated using sympy: series(atan(x)/pi, x, 0, 17)
- constexpr static double POLY_COEFFS[] = {
- 0x1.45f306dc9c889p-2, // x^1: 1/pi
- -0x1.b2995e7b7b60bp-4, // x^3: -1/(3*pi)
- 0x1.04c26be3b06ccp-4, // x^5: 1/(5*pi)
- -0x1.7483758e69c08p-5, // x^7: -1/(7*pi)
- 0x1.21bb945252403p-5, // x^9: 1/(9*pi)
- -0x1.da1bace3cc68ep-6, // x^11: -1/(11*pi)
- 0x1.912b1c2336cf2p-6, // x^13: 1/(13*pi)
- -0x1.5bade52f95e7p-6, // x^15: -1/(15*pi)
- };
- double x_sq = x * x;
- return x * fputil::polyeval(x_sq, POLY_COEFFS[0], POLY_COEFFS[1],
- POLY_COEFFS[2], POLY_COEFFS[3], POLY_COEFFS[4],
- POLY_COEFFS[5], POLY_COEFFS[6], POLY_COEFFS[7]);
- };
-
- // Case 1: |x| <= 0.5 - Direct polynomial evaluation
- if (LIBC_LIKELY(x_abs <= 0.5)) {
- double result = atanpi_eval(x_abs);
- return signed_result(result);
- }
-
- // case 2: 0.5 < |x| <= 1 - use double-angle reduction
- // atan(x) = 2 * atan(x / (1 + sqrt(1 + x^2)))
- // so atanpi(x) = 2 * atanpi(x') where x' = x / (1 + sqrt(1 + x^2))
- if (x_abs <= 1.0) {
- double x_abs_sq = x_abs * x_abs;
- double sqrt_term = fputil::sqrt<double>(1.0 + x_abs_sq);
- double x_prime = x_abs / (1.0 + sqrt_term);
- double result = 2.0 * atanpi_eval(x_prime);
- return signed_result(result);
- }
-
- // case 3: |x| > 1 - use reciprocal transformation
- // atan(x) = pi/2 - atan(1/x) for x > 0
- // so atanpi(x) = 1/2 - atanpi(1/x)
- double x_recip = 1.0 / x_abs;
- double result;
-
- // if 1/|x| > 0.5, we need to apply Case 2 transformation to 1/|x|
- if (x_recip > 0.5) {
- double x_recip_sq = x_recip * x_recip;
- double sqrt_term = fputil::sqrt<double>(1.0 + x_recip_sq);
- double x_prime = x_recip / (1.0 + sqrt_term);
- result = fputil::multiply_add(-2.0, atanpi_eval(x_prime), 0.5);
- } else {
- // direct evaluation since 1/|x| <= 0.5
- result = 0.5 - atanpi_eval(x_recip);
- }
-
- return signed_result(result);
+ return math::atanpif16(x);
}
} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/test/shared/CMakeLists.txt b/libc/test/shared/CMakeLists.txt
index 07ccd0ca1bc4b..48645a6a5ce08 100644
--- a/libc/test/shared/CMakeLists.txt
+++ b/libc/test/shared/CMakeLists.txt
@@ -26,6 +26,7 @@ add_fp_unittest(
libc.src.__support.math.atanf16
libc.src.__support.math.atanhf
libc.src.__support.math.atanhf16
+ libc.src.__support.math.atanpif16
libc.src.__support.math.cbrt
libc.src.__support.math.cbrtf
libc.src.__support.math.cos
diff --git a/libc/test/shared/shared_math_test.cpp b/libc/test/shared/shared_math_test.cpp
index ec70025f0f4ea..9130f2a10cf11 100644
--- a/libc/test/shared/shared_math_test.cpp
+++ b/libc/test/shared/shared_math_test.cpp
@@ -73,6 +73,7 @@ TEST(LlvmLibcSharedMathTest, AllFloat) {
EXPECT_FP_EQ(0x0p+0f, LIBC_NAMESPACE::shared::atan2f(0.0f, 0.0f));
EXPECT_FP_EQ(0x0p+0f, LIBC_NAMESPACE::shared::atanf(0.0f));
EXPECT_FP_EQ(0x0p+0f, LIBC_NAMESPACE::shared::atanhf(0.0f));
+ EXPECT_FP_EQ(0x0p+0, LIBC_NAMESPACE::shared::atanpif16(0.0));
EXPECT_FP_EQ(0x0p+0f, LIBC_NAMESPACE::shared::cbrtf(0.0f));
EXPECT_FP_EQ(0x1p+0f, LIBC_NAMESPACE::shared::cosf(0.0f));
EXPECT_FP_EQ(0x1p+0f, LIBC_NAMESPACE::shared::coshf(0.0f));
diff --git a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
index 83b752ce1214b..a6ce31b5486bd 100644
--- a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
@@ -2593,6 +2593,20 @@ libc_support_library(
],
)
+libc_support_library(
+ name = "__support_math_atanpif16",
+ hdrs = ["src/__support/math/atanpif16.h"],
+ deps = [
+ ":__support_fputil_cast",
+ ":__support_fputil_except_value_utils",
+ ":__support_fputil_fenv_impl",
+ ":__support_fputil_fp_bits",
+ ":__support_fputil_multiply_add",
+ ":__support_fputil_polyeval",
+ ":__support_macros_optimization",
+ ],
+)
+
libc_support_library(
name = "__support_math_asinf",
hdrs = ["src/__support/math/asinf.h"],
@@ -4087,6 +4101,13 @@ libc_math_function(
],
)
+libc_math_function(
+ name = "atanpif16",
+ additional_deps = [
+ ":__support_math_atanpif16",
+ ],
+)
+
libc_math_function(
name = "atan",
additional_deps = [
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