[libc][math] Refactor sinf16 implementation to header-only in src/__support/math folder. by nico · Pull Request #178062 · llvm/llvm-project

nico · 2026-01-26T21:56:44Z

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

llvmbot · 2026-01-26T21:57:45Z

@llvm/pr-subscribers-libc

Author: Nico Weber (nico)

Changes

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

Full diff: https://github.com/llvm/llvm-project/pull/178062.diff

9 Files Affected:

(modified) libc/shared/math.h (+1)
(added) libc/shared/math/sinf16.h (+23)
(modified) libc/src/__support/math/CMakeLists.txt (+17)
(added) libc/src/__support/math/sinf16.h (+130)
(modified) libc/src/math/generic/CMakeLists.txt (+1-12)
(modified) libc/src/math/generic/sinf16.cpp (+2-102)
(modified) libc/test/shared/CMakeLists.txt (+1)
(modified) libc/test/shared/shared_math_test.cpp (+1)
(modified) utils/bazel/llvm-project-overlay/libc/BUILD.bazel (+11-3)

diff --git a/libc/shared/math.h b/libc/shared/math.h
index f7fa175234296..ba37bd52ee8ab 100644
--- a/libc/shared/math.h
+++ b/libc/shared/math.h
@@ -87,6 +87,7 @@
 #include "math/rsqrtf16.h"
 #include "math/sin.h"
 #include "math/sinf.h"
+#include "math/sinf16.h"
 #include "math/tan.h"
 #include "math/tanf.h"
 
diff --git a/libc/shared/math/sinf16.h b/libc/shared/math/sinf16.h
new file mode 100644
index 0000000000000..4c39d8225f672
--- /dev/null
+++ b/libc/shared/math/sinf16.h
@@ -0,0 +1,23 @@
+//===-- Shared sinf16 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_SINF16_H
+#define LLVM_LIBC_SHARED_MATH_SINF16_H
+
+#include "shared/libc_common.h"
+#include "src/__support/math/sinf16.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace shared {
+
+using math::sinf16;
+
+} // namespace shared
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SHARED_MATH_SINF16_H
diff --git a/libc/src/__support/math/CMakeLists.txt b/libc/src/__support/math/CMakeLists.txt
index d37dbe6be6864..6863164a55988 100644
--- a/libc/src/__support/math/CMakeLists.txt
+++ b/libc/src/__support/math/CMakeLists.txt
@@ -1276,6 +1276,23 @@ add_header_library(
     libc.src.__support.macros.optimization
 )
 
+add_header_library(
+  sinf16
+  HDRS
+    sinf16.h
+  DEPENDS
+    .sincosf16_utils
+    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.macros.optimization
+    libc.src.__support.macros.properties.types
+)
+
 add_header_library(
   dfmal
   HDRS
diff --git a/libc/src/__support/math/sinf16.h b/libc/src/__support/math/sinf16.h
new file mode 100644
index 0000000000000..2fcc4e28e1cc9
--- /dev/null
+++ b/libc/src/__support/math/sinf16.h
@@ -0,0 +1,130 @@
+//===-- Half-precision sin(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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_MATH_SINF16_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_SINF16_H
+
+#include "hdr/errno_macros.h"
+#include "hdr/fenv_macros.h"
+#include "sincosf16_utils.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.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/macros/optimization.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+namespace sinf16_internal {
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+LIBC_INLINE_VAR constexpr size_t N_EXCEPTS = 4;
+
+LIBC_INLINE_VAR constexpr fputil::ExceptValues<float16, N_EXCEPTS>
+    SINF16_EXCEPTS{{
+        // (input, RZ output, RU offset, RD offset, RN offset)
+        {0x2b45, 0x2b43, 1, 0, 1},
+        {0x585c, 0x3ba3, 1, 0, 1},
+        {0x5cb0, 0xbbff, 0, 1, 0},
+        {0x51f5, 0xb80f, 0, 1, 0},
+    }};
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+} // namespace sinf16_internal
+
+LIBC_INLINE static float16 sinf16(float16 x) {
+  using namespace sinf16_internal;
+  using namespace sincosf16_internal;
+  using FPBits = fputil::FPBits<float16>;
+  FPBits xbits(x);
+
+  uint16_t x_u = xbits.uintval();
+  uint16_t x_abs = x_u & 0x7fff;
+  float xf = x;
+
+  // Range reduction:
+  // For |x| > pi/32, we perform range reduction as follows:
+  // Find k and y such that:
+  //   x = (k + y) * pi/32
+  //   k is an integer, |y| < 0.5
+  //
+  // This is done by performing:
+  //   k = round(x * 32/pi)
+  //   y = x * 32/pi - k
+  //
+  // Once k and y are computed, we then deduce the answer by the sine of sum
+  // formula:
+  //   sin(x) = sin((k + y) * pi/32)
+  //   	      = sin(k * pi/32) * cos(y * pi/32) +
+  //   	        sin(y * pi/32) * cos(k * pi/32)
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+  // Handle exceptional values
+  bool x_sign = x_u >> 15;
+
+  if (auto r = SINF16_EXCEPTS.lookup_odd(x_abs, x_sign);
+      LIBC_UNLIKELY(r.has_value()))
+    return r.value();
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+  int rounding = fputil::quick_get_round();
+
+  // Exhaustive tests show that for |x| <= 0x1.f4p-11, 1ULP rounding errors
+  // occur. To fix this, the following apply:
+  if (LIBC_UNLIKELY(x_abs <= 0x13d0)) {
+    // sin(+/-0) = +/-0
+    if (LIBC_UNLIKELY(x_abs == 0U))
+      return x;
+
+    // When x > 0, and rounding upward, sin(x) == x.
+    // When x < 0, and rounding downward, sin(x) == x.
+    if ((rounding == FE_UPWARD && xbits.is_pos()) ||
+        (rounding == FE_DOWNWARD && xbits.is_neg()))
+      return x;
+
+    // When x < 0, and rounding upward, sin(x) == (x - 1ULP)
+    if (rounding == FE_UPWARD && xbits.is_neg()) {
+      x_u--;
+      return FPBits(x_u).get_val();
+    }
+  }
+
+  if (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_inf()) {
+      fputil::set_errno_if_required(EDOM);
+      fputil::raise_except_if_required(FE_INVALID);
+    }
+
+    return x + FPBits::quiet_nan().get_val();
+  }
+
+  float sin_k, cos_k, sin_y, cosm1_y;
+  sincosf16_eval(xf, sin_k, cos_k, sin_y, cosm1_y);
+
+  if (LIBC_UNLIKELY(sin_y == 0 && sin_k == 0))
+    return FPBits::zero(xbits.sign()).get_val();
+
+  // Since, cosm1_y = cos_y - 1, therefore:
+  //   sin(x) = cos_k * sin_y + sin_k + (cosm1_y * sin_k)
+  return fputil::cast<float16>(fputil::multiply_add(
+      sin_y, cos_k, fputil::multiply_add(cosm1_y, sin_k, sin_k)));
+}
+
+} // namespace math
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_MATH_SINF16_H
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index 11b87ca93a97c..6a50ec6061eae 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -383,18 +383,7 @@ add_entrypoint_object(
   HDRS
     ../sinf16.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.except_value_utils
-    libc.src.__support.FPUtil.multiply_add
-    libc.src.__support.macros.optimization
-    libc.src.__support.macros.properties.types
-    libc.src.__support.math.sincosf16_utils
-  COMPILE_OPTIONS
-    ${libc_opt_high_flag}
+    libc.src.__support.math.sinf16
 )
 
 add_entrypoint_object(
diff --git a/libc/src/math/generic/sinf16.cpp b/libc/src/math/generic/sinf16.cpp
index 2b579202ea111..611897026cd8f 100644
--- a/libc/src/math/generic/sinf16.cpp
+++ b/libc/src/math/generic/sinf16.cpp
@@ -7,110 +7,10 @@
 //===----------------------------------------------------------------------===//
 
 #include "src/math/sinf16.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/cast.h"
-#include "src/__support/FPUtil/except_value_utils.h"
-#include "src/__support/FPUtil/multiply_add.h"
-#include "src/__support/macros/optimization.h"
-#include "src/__support/math/sincosf16_utils.h"
+#include "src/__support/math/sinf16.h"
 
 namespace LIBC_NAMESPACE_DECL {
 
-#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-constexpr size_t N_EXCEPTS = 4;
-
-constexpr fputil::ExceptValues<float16, N_EXCEPTS> SINF16_EXCEPTS{{
-    // (input, RZ output, RU offset, RD offset, RN offset)
-    {0x2b45, 0x2b43, 1, 0, 1},
-    {0x585c, 0x3ba3, 1, 0, 1},
-    {0x5cb0, 0xbbff, 0, 1, 0},
-    {0x51f5, 0xb80f, 0, 1, 0},
-}};
-#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-
-LLVM_LIBC_FUNCTION(float16, sinf16, (float16 x)) {
-  using namespace sincosf16_internal;
-  using FPBits = fputil::FPBits<float16>;
-  FPBits xbits(x);
-
-  uint16_t x_u = xbits.uintval();
-  uint16_t x_abs = x_u & 0x7fff;
-  float xf = x;
-
-  // Range reduction:
-  // For |x| > pi/32, we perform range reduction as follows:
-  // Find k and y such that:
-  //   x = (k + y) * pi/32
-  //   k is an integer, |y| < 0.5
-  //
-  // This is done by performing:
-  //   k = round(x * 32/pi)
-  //   y = x * 32/pi - k
-  //
-  // Once k and y are computed, we then deduce the answer by the sine of sum
-  // formula:
-  //   sin(x) = sin((k + y) * pi/32)
-  //   	      = sin(k * pi/32) * cos(y * pi/32) +
-  //   	        sin(y * pi/32) * cos(k * pi/32)
-
-#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-  // Handle exceptional values
-  bool x_sign = x_u >> 15;
-
-  if (auto r = SINF16_EXCEPTS.lookup_odd(x_abs, x_sign);
-      LIBC_UNLIKELY(r.has_value()))
-    return r.value();
-#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-
-  int rounding = fputil::quick_get_round();
-
-  // Exhaustive tests show that for |x| <= 0x1.f4p-11, 1ULP rounding errors
-  // occur. To fix this, the following apply:
-  if (LIBC_UNLIKELY(x_abs <= 0x13d0)) {
-    // sin(+/-0) = +/-0
-    if (LIBC_UNLIKELY(x_abs == 0U))
-      return x;
-
-    // When x > 0, and rounding upward, sin(x) == x.
-    // When x < 0, and rounding downward, sin(x) == x.
-    if ((rounding == FE_UPWARD && xbits.is_pos()) ||
-        (rounding == FE_DOWNWARD && xbits.is_neg()))
-      return x;
-
-    // When x < 0, and rounding upward, sin(x) == (x - 1ULP)
-    if (rounding == FE_UPWARD && xbits.is_neg()) {
-      x_u--;
-      return FPBits(x_u).get_val();
-    }
-  }
-
-  if (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_inf()) {
-      fputil::set_errno_if_required(EDOM);
-      fputil::raise_except_if_required(FE_INVALID);
-    }
-
-    return x + FPBits::quiet_nan().get_val();
-  }
-
-  float sin_k, cos_k, sin_y, cosm1_y;
-  sincosf16_eval(xf, sin_k, cos_k, sin_y, cosm1_y);
-
-  if (LIBC_UNLIKELY(sin_y == 0 && sin_k == 0))
-    return FPBits::zero(xbits.sign()).get_val();
-
-  // Since, cosm1_y = cos_y - 1, therefore:
-  //   sin(x) = cos_k * sin_y + sin_k + (cosm1_y * sin_k)
-  return fputil::cast<float16>(fputil::multiply_add(
-      sin_y, cos_k, fputil::multiply_add(cosm1_y, sin_k, sin_k)));
-}
+LLVM_LIBC_FUNCTION(float16, sinf16, (float16 x)) { return math::sinf16(x); }
 
 } // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/test/shared/CMakeLists.txt b/libc/test/shared/CMakeLists.txt
index ef472992fea40..6ee2cba6e1658 100644
--- a/libc/test/shared/CMakeLists.txt
+++ b/libc/test/shared/CMakeLists.txt
@@ -84,6 +84,7 @@ add_fp_unittest(
     libc.src.__support.math.rsqrtf16
     libc.src.__support.math.sin
     libc.src.__support.math.sinf
+    libc.src.__support.math.sinf16
     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 45a7934a83621..cbb32d295389a 100644
--- a/libc/test/shared/shared_math_test.cpp
+++ b/libc/test/shared/shared_math_test.cpp
@@ -51,6 +51,7 @@ TEST(LlvmLibcSharedMathTest, AllFloat16) {
 
   EXPECT_FP_EQ(0x1.921fb6p+0f16, LIBC_NAMESPACE::shared::acosf16(0.0f16));
   EXPECT_FP_EQ(0x1p+0f16, LIBC_NAMESPACE::shared::f16sqrtl(1.0L));
+  EXPECT_FP_EQ(0.0f16, LIBC_NAMESPACE::shared::sinf16(0.0f16));
 }
 
 #endif // LIBC_TYPES_HAS_FLOAT16
diff --git a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
index 09b0a5a8e584a..ba4889a5bdf96 100644
--- a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
@@ -3497,6 +3497,16 @@ libc_support_library(
     ],
 )
 
+libc_support_library(
+    name = "__support_math_sinf16",
+    hdrs = ["src/__support/math/sinf16.h"],
+    deps = [
+        ":__support_fputil_nearest_integer",
+        ":__support_fputil_polyeval",
+        ":__support_math_sincosf16_utils",
+    ],
+)
+
 libc_support_library(
     name = "__support_math_sinhfcoshf_utils",
     hdrs = ["src/__support/math/sinhfcoshf_utils.h"],
@@ -5103,9 +5113,7 @@ libc_math_function(
 libc_math_function(
     name = "sinf16",
     additional_deps = [
-        ":__support_fputil_nearest_integer",
-        ":__support_fputil_polyeval",
-        ":__support_math_sincosf16_utils",
+        ":__support_math_sinf16",
     ],
 )

bassiounix

We need guard macros for float16 type.
Not all platforms has this type so we need to add a guard.
LIBC_TYPES_HAS_FLOAT16 found in include/llvm-libc-macros/float16-macros.h

Also please add the deps accordingly

libc/src/math/generic/CMakeLists.txt

bassiounix · 2026-01-27T03:13:14Z

To have the build running, please resolve conflicts

…upport/math folder. Part of llvm#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

nico · 2026-01-27T03:28:34Z

Done!

bassiounix · 2026-01-27T03:47:23Z

utils/bazel/llvm-project-overlay/libc/BUILD.bazel

+        ":__support_fputil_nearest_integer",
+        ":__support_fputil_polyeval",
+        ":__support_math_sincosf16_utils",
+        ":llvm_libc_macros_float16_macros",


I think for each and every include we want to add its deps

#include "hdr/errno_macros.h" #include "hdr/fenv_macros.h" #include "sincosf16_utils.h" #include "src/__support/FPUtil/FEnvImpl.h" #include "src/__support/FPUtil/FPBits.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/macros/optimization.h"

Per utils/bazel/README.md / https://llvm.org/docs/SupportPolicy.html#peripheral-tier, the bazel build is not supported. If the existing bazel files are missing so much stuff (I'm just moving things around and putting in a best effort), I feel it's not my job to fix them up. The other bots are happy.

…upport/math folder. (llvm#178062) Part of llvm#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

Move the tanpif16 implementation from libc/src/math/generic/tanpif16.cpp into a header-only library at libc/src/__support/math/tanpif16.h, enabling reuse from multiple contexts (libc entrypoint, shared/GPU) without code duplication. The entrypoint .cpp becomes a thin wrapper delegating to math::tanpif16(). A shared header (libc/shared/math/tanpif16.h) re-exports into namespace shared. CMake and Bazel build targets are updated accordingly. Follows the established pattern from cospif16 (llvm#154222) and sinf16 (llvm#178062). Fixes part of llvm#147386. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

nico requested a review from bassiounix January 26, 2026 21:56

nico requested review from aaronmondal, keith and rupprecht as code owners January 26, 2026 21:56

llvmbot added libc bazel "Peripheral" support tier build system: utils/bazel labels Jan 26, 2026

bassiounix requested changes Jan 27, 2026

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bassiounix removed request for aaronmondal, keith and rupprecht January 27, 2026 03:12

nico added 5 commits January 26, 2026 22:20

[libc][math] Refactor sinf16 implementation to header-only in src/__s…

d7f8f1e

…upport/math folder. Part of llvm#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

comments, clang-format

e51f059

windows, bazel

c901e68

deps for float16_macros

c8e8ceb

restore flag

e337ffd

nico force-pushed the libm-sinf16 branch from 0d4ebad to e337ffd Compare January 27, 2026 03:21

nico mentioned this pull request Jan 27, 2026

[libc][math] Tracking Issue - Refactor Higher Math Functions to Header Only #147386

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bassiounix reviewed Jan 27, 2026

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nico merged commit 90829e5 into llvm:main Jan 27, 2026
28 of 29 checks passed

nico deleted the libm-sinf16 branch January 27, 2026 13:17

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[libc][math] Refactor sinf16 implementation to header-only in src/__support/math folder.#178062

[libc][math] Refactor sinf16 implementation to header-only in src/__support/math folder.#178062
nico merged 5 commits intollvm:mainfrom
nico:libm-sinf16

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