[libc][math] Refactor tanf implementation to header-only in src/__support/math folder.#177730
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bassiounix merged 4 commits intollvm:mainfrom Jan 24, 2026
Merged
[libc][math] Refactor tanf implementation to header-only in src/__support/math folder.#177730bassiounix merged 4 commits intollvm:mainfrom
bassiounix merged 4 commits intollvm:mainfrom
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@llvm/pr-subscribers-libc Author: Nico Weber (nico) Changes…port/math folder. Part of #147386 in preparation for: I used #177583 to create the initial version of this. (I updated the script to keep errno where it was, based on the feedback in #177224). Full diff: https://github.com/llvm/llvm-project/pull/177730.diff 9 Files Affected:
diff --git a/libc/shared/math.h b/libc/shared/math.h
index a331abcc033c7..5126e46c9772e 100644
--- a/libc/shared/math.h
+++ b/libc/shared/math.h
@@ -85,5 +85,6 @@
#include "math/rsqrtf16.h"
#include "math/sin.h"
#include "math/tan.h"
+#include "math/tanf.h"
#endif // LLVM_LIBC_SHARED_MATH_H
diff --git a/libc/shared/math/tanf.h b/libc/shared/math/tanf.h
new file mode 100644
index 0000000000000..ce0f11db1ee6a
--- /dev/null
+++ b/libc/shared/math/tanf.h
@@ -0,0 +1,23 @@
+//===-- Shared tanf 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_TANF_H
+#define LLVM_LIBC_SHARED_MATH_TANF_H
+
+#include "shared/libc_common.h"
+#include "src/__support/math/tanf.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace shared {
+
+using math::tanf;
+
+} // namespace shared
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SHARED_MATH_TANF_H
diff --git a/libc/src/__support/math/CMakeLists.txt b/libc/src/__support/math/CMakeLists.txt
index a03952d5c5ed0..b6cb5f17554aa 100644
--- a/libc/src/__support/math/CMakeLists.txt
+++ b/libc/src/__support/math/CMakeLists.txt
@@ -1270,3 +1270,20 @@ add_header_library(
libc.src.__support.FPUtil.multiply_add
libc.src.__support.macros.optimization
)
+
+add_header_library(
+ tanf
+ HDRS
+ tanf.h
+ DEPENDS
+ .range_reduction
+ .sincosf_utils
+ libc.src.__support.FPUtil.except_value_utils
+ libc.src.__support.FPUtil.fenv_impl
+ libc.src.__support.FPUtil.fenv_impl
+ libc.src.__support.FPUtil.fma
+ libc.src.__support.FPUtil.multiply_add
+ libc.src.__support.FPUtil.nearest_integer
+ libc.src.__support.FPUtil.polyeval
+ libc.src.__support.macros.optimization
+)
diff --git a/libc/src/__support/math/tanf.h b/libc/src/__support/math/tanf.h
new file mode 100644
index 0000000000000..980bb98e1cb0e
--- /dev/null
+++ b/libc/src/__support/math/tanf.h
@@ -0,0 +1,164 @@
+//===-- Single-precision tan 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LIBC_SRC___SUPPORT_MATH_TANF_H
+#define LIBC_SRC___SUPPORT_MATH_TANF_H
+
+#include "sincosf_utils.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/multiply_add.h"
+#include "src/__support/FPUtil/nearest_integer.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
+#include "src/__support/macros/properties/cpu_features.h" // LIBC_TARGET_CPU_HAS_FMA
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+namespace tanf_internal {
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+// Exceptional cases for tanf.
+LIBC_INLINE_VAR constexpr size_t N_EXCEPTS = 6;
+
+LIBC_INLINE_VAR constexpr fputil::ExceptValues<float, N_EXCEPTS> TANF_EXCEPTS{{
+ // (inputs, RZ output, RU offset, RD offset, RN offset)
+ // x = 0x1.ada6aap27, tan(x) = 0x1.e80304p-3 (RZ)
+ {0x4d56d355, 0x3e740182, 1, 0, 0},
+ // x = 0x1.862064p33, tan(x) = -0x1.8dee56p-3 (RZ)
+ {0x50431032, 0xbe46f72b, 0, 1, 1},
+ // x = 0x1.af61dap48, tan(x) = 0x1.60d1c6p-2 (RZ)
+ {0x57d7b0ed, 0x3eb068e3, 1, 0, 1},
+ // x = 0x1.0088bcp52, tan(x) = 0x1.ca1edp0 (RZ)
+ {0x5980445e, 0x3fe50f68, 1, 0, 0},
+ // x = 0x1.f90dfcp72, tan(x) = 0x1.597f9cp-1 (RZ)
+ {0x63fc86fe, 0x3f2cbfce, 1, 0, 0},
+ // x = 0x1.a6ce12p86, tan(x) = -0x1.c5612ep-1 (RZ)
+ {0x6ad36709, 0xbf62b097, 0, 1, 0},
+}};
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+} // namespace tanf_internal
+
+LIBC_INLINE static float tanf(float x) {
+ using namespace tanf_internal;
+ using FPBits = typename fputil::FPBits<float>;
+ FPBits xbits(x);
+ uint32_t x_abs = xbits.uintval() & 0x7fff'ffffU;
+
+ // |x| < pi/32
+ if (LIBC_UNLIKELY(x_abs <= 0x3dc9'0fdbU)) {
+ double xd = static_cast<double>(x);
+
+ // |x| < 0x1.0p-12f
+ if (LIBC_UNLIKELY(x_abs < 0x3980'0000U)) {
+ if (LIBC_UNLIKELY(x_abs == 0U)) {
+ // For signed zeros.
+ return x;
+ }
+ // When |x| < 2^-12, the relative error of the approximation tan(x) ~ x
+ // is:
+ // |tan(x) - x| / |tan(x)| < |x^3| / (3|x|)
+ // = x^2 / 3
+ // < 2^-25
+ // < epsilon(1)/2.
+ // So the correctly rounded values of tan(x) are:
+ // = x + sign(x)*eps(x) if rounding mode = FE_UPWARD and x is positive,
+ // or (rounding mode = FE_DOWNWARD and x is
+ // negative),
+ // = x otherwise.
+ // To simplify the rounding decision and make it more efficient, we use
+ // fma(x, 2^-25, x) instead.
+ // 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_CPU_HAS_FMA_FLOAT)
+ return fputil::multiply_add(x, 0x1.0p-25f, x);
+#else
+ return static_cast<float>(fputil::multiply_add(xd, 0x1.0p-25, xd));
+#endif // LIBC_TARGET_CPU_HAS_FMA_FLOAT
+ }
+
+ // |x| < pi/32
+ double xsq = xd * xd;
+
+ // Degree-9 minimax odd polynomial of tan(x) generated by Sollya with:
+ // > P = fpminimax(tan(x)/x, [|0, 2, 4, 6, 8|], [|1, D...|], [0, pi/32]);
+ double result =
+ fputil::polyeval(xsq, 1.0, 0x1.555555553d022p-2, 0x1.111111ce442c1p-3,
+ 0x1.ba180a6bbdecdp-5, 0x1.69c0a88a0b71fp-6);
+ return static_cast<float>(xd * result);
+ }
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+ bool x_sign = xbits.uintval() >> 31;
+ // Check for exceptional values
+ if (LIBC_UNLIKELY(x_abs == 0x3f8a1f62U)) {
+ // |x| = 0x1.143ec4p0
+ float sign = x_sign ? -1.0f : 1.0f;
+
+ // volatile is used to prevent compiler (gcc) from optimizing the
+ // computation, making the results incorrect in different rounding modes.
+ volatile float tmp = 0x1.ddf9f4p0f;
+ tmp = fputil::multiply_add(sign, tmp, sign * 0x1.1p-24f);
+
+ return tmp;
+ }
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+ // |x| > 0x1.ada6a8p+27f
+ if (LIBC_UNLIKELY(x_abs > 0x4d56'd354U)) {
+ // Inf or NaN
+ if (LIBC_UNLIKELY(x_abs >= 0x7f80'0000U)) {
+ if (xbits.is_signaling_nan()) {
+ fputil::raise_except_if_required(FE_INVALID);
+ return FPBits::quiet_nan().get_val();
+ }
+
+ if (x_abs == 0x7f80'0000U) {
+ fputil::set_errno_if_required(EDOM);
+ fputil::raise_except_if_required(FE_INVALID);
+ }
+ return x + FPBits::quiet_nan().get_val();
+ }
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+ // Other large exceptional values
+ if (auto r = TANF_EXCEPTS.lookup_odd(x_abs, x_sign);
+ LIBC_UNLIKELY(r.has_value()))
+ return r.value();
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+ }
+
+ // For |x| >= pi/32, we use the definition of tan(x) function:
+ // tan(x) = sin(x) / cos(x)
+ // The we follow the same computations of sin(x) and cos(x) as sinf, cosf,
+ // and sincosf.
+
+ double xd = static_cast<double>(x);
+ double sin_k, cos_k, sin_y, cosm1_y;
+
+ sincosf_eval(xd, x_abs, sin_k, cos_k, sin_y, cosm1_y);
+ // tan(x) = sin(x) / cos(x)
+ // = (sin_y * cos_k + cos_y * sin_k) / (cos_y * cos_k - sin_y * sin_k)
+ using fputil::multiply_add;
+ return static_cast<float>(
+ multiply_add(sin_y, cos_k, multiply_add(cosm1_y, sin_k, sin_k)) /
+ multiply_add(sin_y, -sin_k, multiply_add(cosm1_y, cos_k, cos_k)));
+}
+
+} // namespace math
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_SRC___SUPPORT_MATH_TANF_H
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index 04ad1aa896613..3addfab6c6603 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -496,17 +496,8 @@ add_entrypoint_object(
HDRS
../tanf.h
DEPENDS
- libc.src.__support.math.range_reduction
- libc.src.__support.math.sincosf_utils
+ libc.src.__support.math.tanf
libc.src.errno.errno
- libc.src.__support.FPUtil.fenv_impl
- libc.src.__support.FPUtil.fenv_impl
- libc.src.__support.FPUtil.except_value_utils
- libc.src.__support.FPUtil.nearest_integer
- libc.src.__support.FPUtil.fma
- libc.src.__support.FPUtil.multiply_add
- libc.src.__support.FPUtil.polyeval
- libc.src.__support.macros.optimization
)
add_entrypoint_object(
diff --git a/libc/src/math/generic/tanf.cpp b/libc/src/math/generic/tanf.cpp
index a8c557b14808c..aee5a6cab2b56 100644
--- a/libc/src/math/generic/tanf.cpp
+++ b/libc/src/math/generic/tanf.cpp
@@ -7,146 +7,10 @@
//===----------------------------------------------------------------------===//
#include "src/math/tanf.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/multiply_add.h"
-#include "src/__support/FPUtil/nearest_integer.h"
-#include "src/__support/common.h"
-#include "src/__support/macros/config.h"
-#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
-#include "src/__support/macros/properties/cpu_features.h" // LIBC_TARGET_CPU_HAS_FMA
-#include "src/__support/math/sincosf_utils.h"
+#include "src/__support/math/tanf.h"
namespace LIBC_NAMESPACE_DECL {
-#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-// Exceptional cases for tanf.
-constexpr size_t N_EXCEPTS = 6;
-
-constexpr fputil::ExceptValues<float, N_EXCEPTS> TANF_EXCEPTS{{
- // (inputs, RZ output, RU offset, RD offset, RN offset)
- // x = 0x1.ada6aap27, tan(x) = 0x1.e80304p-3 (RZ)
- {0x4d56d355, 0x3e740182, 1, 0, 0},
- // x = 0x1.862064p33, tan(x) = -0x1.8dee56p-3 (RZ)
- {0x50431032, 0xbe46f72b, 0, 1, 1},
- // x = 0x1.af61dap48, tan(x) = 0x1.60d1c6p-2 (RZ)
- {0x57d7b0ed, 0x3eb068e3, 1, 0, 1},
- // x = 0x1.0088bcp52, tan(x) = 0x1.ca1edp0 (RZ)
- {0x5980445e, 0x3fe50f68, 1, 0, 0},
- // x = 0x1.f90dfcp72, tan(x) = 0x1.597f9cp-1 (RZ)
- {0x63fc86fe, 0x3f2cbfce, 1, 0, 0},
- // x = 0x1.a6ce12p86, tan(x) = -0x1.c5612ep-1 (RZ)
- {0x6ad36709, 0xbf62b097, 0, 1, 0},
-}};
-#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-
-LLVM_LIBC_FUNCTION(float, tanf, (float x)) {
- using FPBits = typename fputil::FPBits<float>;
- FPBits xbits(x);
- uint32_t x_abs = xbits.uintval() & 0x7fff'ffffU;
-
- // |x| < pi/32
- if (LIBC_UNLIKELY(x_abs <= 0x3dc9'0fdbU)) {
- double xd = static_cast<double>(x);
-
- // |x| < 0x1.0p-12f
- if (LIBC_UNLIKELY(x_abs < 0x3980'0000U)) {
- if (LIBC_UNLIKELY(x_abs == 0U)) {
- // For signed zeros.
- return x;
- }
- // When |x| < 2^-12, the relative error of the approximation tan(x) ~ x
- // is:
- // |tan(x) - x| / |tan(x)| < |x^3| / (3|x|)
- // = x^2 / 3
- // < 2^-25
- // < epsilon(1)/2.
- // So the correctly rounded values of tan(x) are:
- // = x + sign(x)*eps(x) if rounding mode = FE_UPWARD and x is positive,
- // or (rounding mode = FE_DOWNWARD and x is
- // negative),
- // = x otherwise.
- // To simplify the rounding decision and make it more efficient, we use
- // fma(x, 2^-25, x) instead.
- // 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_CPU_HAS_FMA_FLOAT)
- return fputil::multiply_add(x, 0x1.0p-25f, x);
-#else
- return static_cast<float>(fputil::multiply_add(xd, 0x1.0p-25, xd));
-#endif // LIBC_TARGET_CPU_HAS_FMA_FLOAT
- }
-
- // |x| < pi/32
- double xsq = xd * xd;
-
- // Degree-9 minimax odd polynomial of tan(x) generated by Sollya with:
- // > P = fpminimax(tan(x)/x, [|0, 2, 4, 6, 8|], [|1, D...|], [0, pi/32]);
- double result =
- fputil::polyeval(xsq, 1.0, 0x1.555555553d022p-2, 0x1.111111ce442c1p-3,
- 0x1.ba180a6bbdecdp-5, 0x1.69c0a88a0b71fp-6);
- return static_cast<float>(xd * result);
- }
-
-#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
- bool x_sign = xbits.uintval() >> 31;
- // Check for exceptional values
- if (LIBC_UNLIKELY(x_abs == 0x3f8a1f62U)) {
- // |x| = 0x1.143ec4p0
- float sign = x_sign ? -1.0f : 1.0f;
-
- // volatile is used to prevent compiler (gcc) from optimizing the
- // computation, making the results incorrect in different rounding modes.
- volatile float tmp = 0x1.ddf9f4p0f;
- tmp = fputil::multiply_add(sign, tmp, sign * 0x1.1p-24f);
-
- return tmp;
- }
-#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-
- // |x| > 0x1.ada6a8p+27f
- if (LIBC_UNLIKELY(x_abs > 0x4d56'd354U)) {
- // Inf or NaN
- if (LIBC_UNLIKELY(x_abs >= 0x7f80'0000U)) {
- if (xbits.is_signaling_nan()) {
- fputil::raise_except_if_required(FE_INVALID);
- return FPBits::quiet_nan().get_val();
- }
-
- if (x_abs == 0x7f80'0000U) {
- fputil::set_errno_if_required(EDOM);
- fputil::raise_except_if_required(FE_INVALID);
- }
- return x + FPBits::quiet_nan().get_val();
- }
-#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
- // Other large exceptional values
- if (auto r = TANF_EXCEPTS.lookup_odd(x_abs, x_sign);
- LIBC_UNLIKELY(r.has_value()))
- return r.value();
-#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
- }
-
- // For |x| >= pi/32, we use the definition of tan(x) function:
- // tan(x) = sin(x) / cos(x)
- // The we follow the same computations of sin(x) and cos(x) as sinf, cosf,
- // and sincosf.
-
- double xd = static_cast<double>(x);
- double sin_k, cos_k, sin_y, cosm1_y;
-
- sincosf_eval(xd, x_abs, sin_k, cos_k, sin_y, cosm1_y);
- // tan(x) = sin(x) / cos(x)
- // = (sin_y * cos_k + cos_y * sin_k) / (cos_y * cos_k - sin_y * sin_k)
- using fputil::multiply_add;
- return static_cast<float>(
- multiply_add(sin_y, cos_k, multiply_add(cosm1_y, sin_k, sin_k)) /
- multiply_add(sin_y, -sin_k, multiply_add(cosm1_y, cos_k, cos_k)));
-}
+LLVM_LIBC_FUNCTION(float, tanf, (float x)) { return math::tanf(x); }
} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/test/shared/CMakeLists.txt b/libc/test/shared/CMakeLists.txt
index 4f82d00cc6c84..dabf5f6b168cc 100644
--- a/libc/test/shared/CMakeLists.txt
+++ b/libc/test/shared/CMakeLists.txt
@@ -81,4 +81,5 @@ add_fp_unittest(
libc.src.__support.math.rsqrtf16
libc.src.__support.math.sin
libc.src.__support.math.tan
+ libc.src.__support.math.tanf
)
diff --git a/libc/test/shared/shared_math_test.cpp b/libc/test/shared/shared_math_test.cpp
index 5ec8a7b23081e..bb03d886183c8 100644
--- a/libc/test/shared/shared_math_test.cpp
+++ b/libc/test/shared/shared_math_test.cpp
@@ -89,6 +89,7 @@ TEST(LlvmLibcSharedMathTest, AllFloat) {
EXPECT_EQ(long(0), LIBC_NAMESPACE::shared::llogbf(1.0f));
EXPECT_FP_EQ(0x0p+0f, LIBC_NAMESPACE::shared::logbf(1.0f));
EXPECT_FP_EQ(0x1p+0f, LIBC_NAMESPACE::shared::rsqrtf(1.0f));
+ EXPECT_FP_EQ(0.0f, LIBC_NAMESPACE::shared::tan(0.0f));
}
TEST(LlvmLibcSharedMathTest, AllDouble) {
diff --git a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
index 853182ce18b57..33e55a9bda52f 100644
--- a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
@@ -3492,6 +3492,21 @@ libc_support_library(
],
)
+libc_support_library(
+ name = "__support_math_tanf",
+ hdrs = ["src/__support/math/tanf.h"],
+ deps = [
+ ":__support_fputil_fma",
+ ":__support_fputil_multiply_add",
+ ":__support_fputil_nearest_integer",
+ ":__support_fputil_polyeval",
+ ":__support_macros_optimization",
+ ":__support_macros_properties_cpu_features",
+ ":__support_range_reduction",
+ ":__support_sincosf_utils",
+ ],
+)
+
############################### complex targets ################################
libc_function(
@@ -5166,14 +5181,7 @@ libc_math_function(
libc_math_function(
name = "tanf",
additional_deps = [
- ":__support_fputil_fma",
- ":__support_fputil_multiply_add",
- ":__support_fputil_nearest_integer",
- ":__support_fputil_polyeval",
- ":__support_macros_optimization",
- ":__support_macros_properties_cpu_features",
- ":__support_range_reduction",
- ":__support_sincosf_utils",
+ ":__support_math_tanf",
],
)
|
🐧 Linux x64 Test Results✅ The build succeeded and no tests ran. This is expected in some build configurations. |
bassiounix
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Jan 29, 2026
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Feb 4, 2026
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Part of #147386
in preparation for:
https://discourse.llvm.org/t/rfc-make-clang-builtin-math-functions-constexpr-with-llvm-libc-to-support-c-23-constexpr-math-functions/86450
I used #177583 to create the initial version of this. (I updated the script to keep errno where it was, based on the feedback in #177224).