[libc-commits] [libc] [llvm] [libc][math] Refactor sin implementation to header-only in src/__support/math folder. (PR #175200)
via libc-commits
libc-commits at lists.llvm.org
Fri Jan 9 08:45:37 PST 2026
https://github.com/lntue created https://github.com/llvm/llvm-project/pull/175200
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
>From 8a91c3f9f61e2db4bdb5264b9fd497ca8a7cd945 Mon Sep 17 00:00:00 2001
From: Tue Ly <lntue.h at gmail.com>
Date: Fri, 9 Jan 2026 16:43:05 +0000
Subject: [PATCH] [libc][math] Refactor sin implementation to header-only in
src/__support/math folder.
---
libc/shared/math.h | 1 +
libc/shared/math/sin.h | 23 +++
libc/src/__support/math/CMakeLists.txt | 16 ++
libc/src/__support/math/sin.h | 181 ++++++++++++++++++
libc/src/math/generic/CMakeLists.txt | 12 +-
libc/src/math/generic/sin.cpp | 168 +---------------
libc/test/shared/CMakeLists.txt | 1 +
libc/test/shared/shared_math_test.cpp | 1 +
.../llvm-project-overlay/libc/BUILD.bazel | 18 +-
9 files changed, 239 insertions(+), 182 deletions(-)
create mode 100644 libc/shared/math/sin.h
create mode 100644 libc/src/__support/math/sin.h
diff --git a/libc/shared/math.h b/libc/shared/math.h
index 70c6d375c22de..6f7805bc5e7ac 100644
--- a/libc/shared/math.h
+++ b/libc/shared/math.h
@@ -64,5 +64,6 @@
#include "math/ldexpf16.h"
#include "math/rsqrtf.h"
#include "math/rsqrtf16.h"
+#include "math/sin.h"
#endif // LLVM_LIBC_SHARED_MATH_H
diff --git a/libc/shared/math/sin.h b/libc/shared/math/sin.h
new file mode 100644
index 0000000000000..011cec6d8e2ed
--- /dev/null
+++ b/libc/shared/math/sin.h
@@ -0,0 +1,23 @@
+//===-- Shared sin 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_SIN_H
+#define LLVM_LIBC_SHARED_MATH_SIN_H
+
+#include "shared/libc_common.h"
+#include "src/__support/math/sin.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace shared {
+
+using math::sin;
+
+} // namespace shared
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SHARED_MATH_SIN_H
diff --git a/libc/src/__support/math/CMakeLists.txt b/libc/src/__support/math/CMakeLists.txt
index f8622da52d983..e41cfec980ff9 100644
--- a/libc/src/__support/math/CMakeLists.txt
+++ b/libc/src/__support/math/CMakeLists.txt
@@ -1008,3 +1008,19 @@ add_header_library(
.exp10f_utils
libc.src.__support.FPUtil.multiply_add
)
+
+add_header_library(
+ sin
+ HDRS
+ sin.h
+ DEPENDS
+ libc.hdr.errno_macros
+ libc.src.errno.errno
+ libc.src.__support.FPUtil.double_double
+ libc.src.__support.FPUtil.dyadic_float
+ libc.src.__support.FPUtil.fenv_impl
+ libc.src.__support.FPUtil.fp_bits
+ libc.src.__support.math.range_reduction_double
+ libc.src.__support.math.sincos_eval
+ libc.src.__support.macros.optimization
+)
diff --git a/libc/src/__support/math/sin.h b/libc/src/__support/math/sin.h
new file mode 100644
index 0000000000000..af1eb59118c2d
--- /dev/null
+++ b/libc/src/__support/math/sin.h
@@ -0,0 +1,181 @@
+//===-- Implementation header for sin ---------------------------*- 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 LIBC_SRC___SUPPORT_MATH_SIN_H
+#define LIBC_SRC___SUPPORT_MATH_SIN_H
+
+#include "range_reduction_double_common.h"
+#include "sincos_eval.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/double_double.h"
+#include "src/__support/FPUtil/dyadic_float.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
+
+#ifdef LIBC_TARGET_CPU_HAS_FMA_DOUBLE
+#include "range_reduction_double_fma.h"
+#else
+#include "range_reduction_double_nofma.h"
+#endif // LIBC_TARGET_CPU_HAS_FMA_DOUBLE
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+LIBC_INLINE static constexpr double sin(double x) {
+ using namespace math::range_reduction_double_internal;
+ using FPBits = typename fputil::FPBits<double>;
+ FPBits xbits(x);
+
+ uint16_t x_e = xbits.get_biased_exponent();
+
+ DoubleDouble y;
+ unsigned k = 0;
+ LargeRangeReduction range_reduction_large{};
+
+ // |x| < 2^16
+ if (LIBC_LIKELY(x_e < FPBits::EXP_BIAS + FAST_PASS_EXPONENT)) {
+ // |x| < 2^-7
+ if (LIBC_UNLIKELY(x_e < FPBits::EXP_BIAS - 7)) {
+ // |x| < 2^-26, |sin(x) - x| < ulp(x)/2.
+ if (LIBC_UNLIKELY(x_e < FPBits::EXP_BIAS - 26)) {
+ // Signed zeros.
+ if (LIBC_UNLIKELY(x == 0.0))
+ return x + x; // Make sure it works with FTZ/DAZ.
+
+#ifdef LIBC_TARGET_CPU_HAS_FMA_DOUBLE
+ return fputil::multiply_add(x, -0x1.0p-54, x);
+#else
+ if (LIBC_UNLIKELY(x_e < 4)) {
+ int rounding_mode = fputil::quick_get_round();
+ if (rounding_mode == FE_TOWARDZERO ||
+ (xbits.sign() == Sign::POS && rounding_mode == FE_DOWNWARD) ||
+ (xbits.sign() == Sign::NEG && rounding_mode == FE_UPWARD))
+ return FPBits(xbits.uintval() - 1).get_val();
+ }
+ return fputil::multiply_add(x, -0x1.0p-54, x);
+#endif // LIBC_TARGET_CPU_HAS_FMA_DOUBLE
+ }
+ // No range reduction needed.
+ k = 0;
+ y.lo = 0.0;
+ y.hi = x;
+ } else {
+ // Small range reduction.
+ k = range_reduction_small(x, y);
+ }
+ } else {
+ // Inf or NaN
+ if (LIBC_UNLIKELY(x_e > 2 * FPBits::EXP_BIAS)) {
+ // sin(+-Inf) = NaN
+ if (xbits.is_signaling_nan()) {
+ fputil::raise_except_if_required(FE_INVALID);
+ return FPBits::quiet_nan().get_val();
+ }
+
+ if (xbits.get_mantissa() == 0) {
+ fputil::set_errno_if_required(EDOM);
+ fputil::raise_except_if_required(FE_INVALID);
+ }
+ return x + FPBits::quiet_nan().get_val();
+ }
+
+ // Large range reduction.
+ k = range_reduction_large.fast(x, y);
+ }
+
+ DoubleDouble sin_y, cos_y;
+
+ [[maybe_unused]] double err =
+ math::sincos_eval_internal::sincos_eval(y, sin_y, cos_y);
+
+ // Look up sin(k * pi/128) and cos(k * pi/128)
+#ifdef LIBC_MATH_HAS_SMALL_TABLES
+ // Memory saving versions. Use 65-entry table.
+ auto get_idx_dd = [](unsigned kk) -> DoubleDouble {
+ unsigned idx = (kk & 64) ? 64 - (kk & 63) : (kk & 63);
+ DoubleDouble ans = SIN_K_PI_OVER_128[idx];
+ if (kk & 128) {
+ ans.hi = -ans.hi;
+ ans.lo = -ans.lo;
+ }
+ return ans;
+ };
+ DoubleDouble sin_k = get_idx_dd(k);
+ DoubleDouble cos_k = get_idx_dd(k + 64);
+#else
+ // Fast look up version, but needs 256-entry table.
+ // cos(k * pi/128) = sin(k * pi/128 + pi/2) = sin((k + 64) * pi/128).
+ DoubleDouble sin_k = SIN_K_PI_OVER_128[k & 255];
+ DoubleDouble cos_k = SIN_K_PI_OVER_128[(k + 64) & 255];
+#endif
+
+ // After range reduction, k = round(x * 128 / pi) and y = x - k * (pi / 128).
+ // So k is an integer and -pi / 256 <= y <= pi / 256.
+ // Then sin(x) = sin((k * pi/128 + y)
+ // = sin(y) * cos(k*pi/128) + cos(y) * sin(k*pi/128)
+ DoubleDouble sin_k_cos_y = fputil::quick_mult(cos_y, sin_k);
+ DoubleDouble cos_k_sin_y = fputil::quick_mult(sin_y, cos_k);
+
+ DoubleDouble rr = fputil::exact_add<false>(sin_k_cos_y.hi, cos_k_sin_y.hi);
+ rr.lo += sin_k_cos_y.lo + cos_k_sin_y.lo;
+
+#ifdef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+ return rr.hi + rr.lo;
+#else
+ // Accurate test and pass for correctly rounded implementation.
+
+ double rlp = rr.lo + err;
+ double rlm = rr.lo - err;
+
+ double r_upper = rr.hi + rlp; // (rr.lo + ERR);
+ double r_lower = rr.hi + rlm; // (rr.lo - ERR);
+
+ // Ziv's rounding test.
+ if (LIBC_LIKELY(r_upper == r_lower))
+ return r_upper;
+
+ Float128 u_f128, sin_u, cos_u;
+ if (LIBC_LIKELY(x_e < FPBits::EXP_BIAS + FAST_PASS_EXPONENT))
+ u_f128 = range_reduction_small_f128(x);
+ else
+ u_f128 = range_reduction_large.accurate();
+
+ math::sincos_eval_internal::sincos_eval(u_f128, sin_u, cos_u);
+
+ auto get_sin_k = [](unsigned kk) -> Float128 {
+ unsigned idx = (kk & 64) ? 64 - (kk & 63) : (kk & 63);
+ Float128 ans = SIN_K_PI_OVER_128_F128[idx];
+ if (kk & 128)
+ ans.sign = Sign::NEG;
+ return ans;
+ };
+
+ // cos(k * pi/128) = sin(k * pi/128 + pi/2) = sin((k + 64) * pi/128).
+ Float128 sin_k_f128 = get_sin_k(k);
+ Float128 cos_k_f128 = get_sin_k(k + 64);
+
+ // sin(x) = sin(k * pi/128 + u)
+ // = sin(u) * cos(k*pi/128) + cos(u) * sin(k*pi/128)
+ Float128 r = fputil::quick_add(fputil::quick_mul(sin_k_f128, cos_u),
+ fputil::quick_mul(cos_k_f128, sin_u));
+
+ // TODO: Add assertion if Ziv's accuracy tests fail in debug mode.
+ // https://github.com/llvm/llvm-project/issues/96452.
+
+ return static_cast<double>(r);
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+}
+
+} // namespace math
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_SRC___SUPPORT_MATH_SIN_H
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index e343c1f15c3f1..97c41c47f70f1 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -363,17 +363,7 @@ add_entrypoint_object(
HDRS
../sin.h
DEPENDS
- libc.src.__support.math.range_reduction_double
- libc.src.__support.math.sincos_eval
- libc.hdr.errno_macros
- libc.src.errno.errno
- libc.src.__support.FPUtil.double_double
- libc.src.__support.FPUtil.dyadic_float
- libc.src.__support.FPUtil.fenv_impl
- libc.src.__support.FPUtil.fp_bits
- libc.src.__support.FPUtil.multiply_add
- libc.src.__support.FPUtil.rounding_mode
- libc.src.__support.macros.optimization
+ libc.src.__support.math.sin
)
add_entrypoint_object(
diff --git a/libc/src/math/generic/sin.cpp b/libc/src/math/generic/sin.cpp
index 1b6310f99366c..6d758d8450bc2 100644
--- a/libc/src/math/generic/sin.cpp
+++ b/libc/src/math/generic/sin.cpp
@@ -7,174 +7,10 @@
//===----------------------------------------------------------------------===//
#include "src/math/sin.h"
-#include "hdr/errno_macros.h"
-#include "src/__support/FPUtil/FEnvImpl.h"
-#include "src/__support/FPUtil/FPBits.h"
-#include "src/__support/FPUtil/double_double.h"
-#include "src/__support/FPUtil/dyadic_float.h"
-#include "src/__support/FPUtil/multiply_add.h"
-#include "src/__support/FPUtil/rounding_mode.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/range_reduction_double_common.h"
-#include "src/__support/math/sincos_eval.h"
-
-#ifdef LIBC_TARGET_CPU_HAS_FMA_DOUBLE
-#include "src/__support/math/range_reduction_double_fma.h"
-#else
-#include "src/__support/math/range_reduction_double_nofma.h"
-#endif // LIBC_TARGET_CPU_HAS_FMA_DOUBLE
+#include "src/__support/math/sin.h"
namespace LIBC_NAMESPACE_DECL {
-using DoubleDouble = fputil::DoubleDouble;
-using Float128 = typename fputil::DyadicFloat<128>;
-
-LLVM_LIBC_FUNCTION(double, sin, (double x)) {
- using namespace math::range_reduction_double_internal;
- using FPBits = typename fputil::FPBits<double>;
- FPBits xbits(x);
-
- uint16_t x_e = xbits.get_biased_exponent();
-
- DoubleDouble y;
- unsigned k;
- LargeRangeReduction range_reduction_large{};
-
- // |x| < 2^16
- if (LIBC_LIKELY(x_e < FPBits::EXP_BIAS + FAST_PASS_EXPONENT)) {
- // |x| < 2^-7
- if (LIBC_UNLIKELY(x_e < FPBits::EXP_BIAS - 7)) {
- // |x| < 2^-26, |sin(x) - x| < ulp(x)/2.
- if (LIBC_UNLIKELY(x_e < FPBits::EXP_BIAS - 26)) {
- // Signed zeros.
- if (LIBC_UNLIKELY(x == 0.0))
- return x + x; // Make sure it works with FTZ/DAZ.
-
-#ifdef LIBC_TARGET_CPU_HAS_FMA_DOUBLE
- return fputil::multiply_add(x, -0x1.0p-54, x);
-#else
- if (LIBC_UNLIKELY(x_e < 4)) {
- int rounding_mode = fputil::quick_get_round();
- if (rounding_mode == FE_TOWARDZERO ||
- (xbits.sign() == Sign::POS && rounding_mode == FE_DOWNWARD) ||
- (xbits.sign() == Sign::NEG && rounding_mode == FE_UPWARD))
- return FPBits(xbits.uintval() - 1).get_val();
- }
- return fputil::multiply_add(x, -0x1.0p-54, x);
-#endif // LIBC_TARGET_CPU_HAS_FMA_DOUBLE
- }
- // No range reduction needed.
- k = 0;
- y.lo = 0.0;
- y.hi = x;
- } else {
- // Small range reduction.
- k = range_reduction_small(x, y);
- }
- } else {
- // Inf or NaN
- if (LIBC_UNLIKELY(x_e > 2 * FPBits::EXP_BIAS)) {
- // sin(+-Inf) = NaN
- if (xbits.is_signaling_nan()) {
- fputil::raise_except_if_required(FE_INVALID);
- return FPBits::quiet_nan().get_val();
- }
-
- if (xbits.get_mantissa() == 0) {
- fputil::set_errno_if_required(EDOM);
- fputil::raise_except_if_required(FE_INVALID);
- }
- return x + FPBits::quiet_nan().get_val();
- }
-
- // Large range reduction.
- k = range_reduction_large.fast(x, y);
- }
-
- DoubleDouble sin_y, cos_y;
-
- [[maybe_unused]] double err =
- math::sincos_eval_internal::sincos_eval(y, sin_y, cos_y);
-
- // Look up sin(k * pi/128) and cos(k * pi/128)
-#ifdef LIBC_MATH_HAS_SMALL_TABLES
- // Memory saving versions. Use 65-entry table.
- auto get_idx_dd = [](unsigned kk) -> DoubleDouble {
- unsigned idx = (kk & 64) ? 64 - (kk & 63) : (kk & 63);
- DoubleDouble ans = SIN_K_PI_OVER_128[idx];
- if (kk & 128) {
- ans.hi = -ans.hi;
- ans.lo = -ans.lo;
- }
- return ans;
- };
- DoubleDouble sin_k = get_idx_dd(k);
- DoubleDouble cos_k = get_idx_dd(k + 64);
-#else
- // Fast look up version, but needs 256-entry table.
- // cos(k * pi/128) = sin(k * pi/128 + pi/2) = sin((k + 64) * pi/128).
- DoubleDouble sin_k = SIN_K_PI_OVER_128[k & 255];
- DoubleDouble cos_k = SIN_K_PI_OVER_128[(k + 64) & 255];
-#endif
-
- // After range reduction, k = round(x * 128 / pi) and y = x - k * (pi / 128).
- // So k is an integer and -pi / 256 <= y <= pi / 256.
- // Then sin(x) = sin((k * pi/128 + y)
- // = sin(y) * cos(k*pi/128) + cos(y) * sin(k*pi/128)
- DoubleDouble sin_k_cos_y = fputil::quick_mult(cos_y, sin_k);
- DoubleDouble cos_k_sin_y = fputil::quick_mult(sin_y, cos_k);
-
- DoubleDouble rr = fputil::exact_add<false>(sin_k_cos_y.hi, cos_k_sin_y.hi);
- rr.lo += sin_k_cos_y.lo + cos_k_sin_y.lo;
-
-#ifdef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
- return rr.hi + rr.lo;
-#else
- // Accurate test and pass for correctly rounded implementation.
-
- double rlp = rr.lo + err;
- double rlm = rr.lo - err;
-
- double r_upper = rr.hi + rlp; // (rr.lo + ERR);
- double r_lower = rr.hi + rlm; // (rr.lo - ERR);
-
- // Ziv's rounding test.
- if (LIBC_LIKELY(r_upper == r_lower))
- return r_upper;
-
- Float128 u_f128, sin_u, cos_u;
- if (LIBC_LIKELY(x_e < FPBits::EXP_BIAS + FAST_PASS_EXPONENT))
- u_f128 = range_reduction_small_f128(x);
- else
- u_f128 = range_reduction_large.accurate();
-
- math::sincos_eval_internal::sincos_eval(u_f128, sin_u, cos_u);
-
- auto get_sin_k = [](unsigned kk) -> Float128 {
- unsigned idx = (kk & 64) ? 64 - (kk & 63) : (kk & 63);
- Float128 ans = SIN_K_PI_OVER_128_F128[idx];
- if (kk & 128)
- ans.sign = Sign::NEG;
- return ans;
- };
-
- // cos(k * pi/128) = sin(k * pi/128 + pi/2) = sin((k + 64) * pi/128).
- Float128 sin_k_f128 = get_sin_k(k);
- Float128 cos_k_f128 = get_sin_k(k + 64);
-
- // sin(x) = sin(k * pi/128 + u)
- // = sin(u) * cos(k*pi/128) + cos(u) * sin(k*pi/128)
- Float128 r = fputil::quick_add(fputil::quick_mul(sin_k_f128, cos_u),
- fputil::quick_mul(cos_k_f128, sin_u));
-
- // TODO: Add assertion if Ziv's accuracy tests fail in debug mode.
- // https://github.com/llvm/llvm-project/issues/96452.
-
- return static_cast<double>(r);
-#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-}
+LLVM_LIBC_FUNCTION(double, sin, (double x)) { return math::sin(x); }
} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/test/shared/CMakeLists.txt b/libc/test/shared/CMakeLists.txt
index 4482d6344ae03..70849de9fb59c 100644
--- a/libc/test/shared/CMakeLists.txt
+++ b/libc/test/shared/CMakeLists.txt
@@ -60,4 +60,5 @@ add_fp_unittest(
libc.src.__support.math.ldexpf16
libc.src.__support.math.rsqrtf
libc.src.__support.math.rsqrtf16
+ libc.src.__support.math.sin
)
diff --git a/libc/test/shared/shared_math_test.cpp b/libc/test/shared/shared_math_test.cpp
index f09b0dcd4ef9f..fc05e535f9266 100644
--- a/libc/test/shared/shared_math_test.cpp
+++ b/libc/test/shared/shared_math_test.cpp
@@ -89,6 +89,7 @@ TEST(LlvmLibcSharedMathTest, AllDouble) {
EXPECT_FP_EQ(0x1p+0, LIBC_NAMESPACE::shared::exp2(0.0));
EXPECT_FP_EQ(0x1p+0, LIBC_NAMESPACE::shared::exp10(0.0));
EXPECT_FP_EQ(0x0p+0, LIBC_NAMESPACE::shared::expm1(0.0));
+ EXPECT_FP_EQ(0.0, LIBC_NAMESPACE::shared::sin(0.0));
}
#ifdef LIBC_TYPES_HAS_FLOAT128
diff --git a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
index 913e913572b14..ac41bd359f0d4 100644
--- a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
@@ -3176,6 +3176,18 @@ libc_support_library(
],
)
+libc_support_library(
+ name = "__support_math_sin",
+ hdrs = ["src/__support/math/sin.h"],
+ deps = [
+ ":__support_fputil_multiply_add",
+ ":__support_macros_optimization",
+ ":__support_macros_properties_cpu_features",
+ ":__support_range_reduction_double",
+ ":__support_sincos_eval",
+ ],
+)
+
libc_support_library(
name = "__support_math_sinhfcoshf_utils",
hdrs = ["src/__support/math/sinhfcoshf_utils.h"],
@@ -4732,11 +4744,7 @@ libc_math_function(name = "setpayloadsigf16")
libc_math_function(
name = "sin",
additional_deps = [
- ":__support_fputil_multiply_add",
- ":__support_macros_optimization",
- ":__support_macros_properties_cpu_features",
- ":__support_range_reduction_double",
- ":__support_sincos_eval",
+ ":__support_math_sin",
],
)
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