[libc][math] Refactor expf16 implementation to header-only in src/__support/math folder. by bassiounix · Pull Request #147428 · llvm/llvm-project

bassiounix · 2025-07-08T00:00:08Z

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

@lntue @michaelrj-google @vonosmas @overmighty @jhuber6

…upport/math folder.

llvmbot · 2025-07-08T00:00:41Z

@llvm/pr-subscribers-libc

Author: Muhammad Bassiouni (bassiounix)

Changes

Part of [https://github.com//issues/147386](#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

@lntue @michaelrj-google @vonosmas @overmighty @jhuber6

Full diff: https://github.com/llvm/llvm-project/pull/147428.diff

8 Files Affected:

(modified) libc/shared/math.h (+1)
(added) libc/shared/math/expf16.h (+23)
(modified) libc/src/__support/math/CMakeLists.txt (+28)
(added) libc/src/__support/math/exp_float16_constants.h (+38)
(added) libc/src/__support/math/expf16.h (+116)
(modified) libc/src/math/generic/CMakeLists.txt (+1-13)
(modified) libc/src/math/generic/expf16.cpp (+3-112)
(modified) utils/bazel/llvm-project-overlay/libc/BUILD.bazel (+29)

diff --git a/libc/shared/math.h b/libc/shared/math.h
index 4ddc29c7ae834..9db53b69041d0 100644
--- a/libc/shared/math.h
+++ b/libc/shared/math.h
@@ -12,5 +12,6 @@
 #include "libc_common.h"
 
 #include "math/expf.h"
+#include "math/expf16.h"
 
 #endif // LLVM_LIBC_SHARED_MATH_H
diff --git a/libc/shared/math/expf16.h b/libc/shared/math/expf16.h
new file mode 100644
index 0000000000000..4e6ab78b26467
--- /dev/null
+++ b/libc/shared/math/expf16.h
@@ -0,0 +1,23 @@
+//===-- Shared expf16 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_EXPF16_H
+#define LLVM_LIBC_SHARED_MATH_EXPF16_H
+
+#include "shared/libc_common.h"
+#include "src/__support/math/expf16.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace shared {
+
+using math::expf16;
+
+} // namespace shared
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SHARED_MATH_EXPF16_H
diff --git a/libc/src/__support/math/CMakeLists.txt b/libc/src/__support/math/CMakeLists.txt
index 66c1d19a1cab0..6d4d548f2e48f 100644
--- a/libc/src/__support/math/CMakeLists.txt
+++ b/libc/src/__support/math/CMakeLists.txt
@@ -22,3 +22,31 @@ add_header_library(
     libc.src.__support.macros.config
     libc.src.__support.macros.optimization
 )
+
+add_header_library(
+  exp_float16_constants
+  HDRS
+    exp_float16_constants.h
+  DEPENDS
+    libc.src.__support.FPUtil.except_value_utils
+)
+
+add_header_library(
+  expf16
+  HDRS
+    expf16.h
+  DEPENDS
+    .expxf16
+    libc.hdr.errno_macros
+    libc.hdr.fenv_macros
+    libc.src.__support.CPP.array
+    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.FPUtil.nearest_integer
+    libc.src.__support.FPUtil.polyeval
+    libc.src.__support.FPUtil.rounding_mode
+    libc.src.__support.macros.optimization
+)
diff --git a/libc/src/__support/math/exp_float16_constants.h b/libc/src/__support/math/exp_float16_constants.h
new file mode 100644
index 0000000000000..9c3aa05e9551c
--- /dev/null
+++ b/libc/src/__support/math/exp_float16_constants.h
@@ -0,0 +1,38 @@
+//===-- High and Low Excepts for expf16 functions ---------------*- 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_EXP_FLOAT16_CONSTANTS_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_EXP_FLOAT16_CONSTANTS_H
+
+#include "src/__support/FPUtil/except_value_utils.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+static constexpr fputil::ExceptValues<float16, 2> EXPF16_EXCEPTS_LO = {{
+    // (input, RZ output, RU offset, RD offset, RN offset)
+    // x = 0x1.de4p-8, expf16(x) = 0x1.01cp+0 (RZ)
+    {0x1f79U, 0x3c07U, 1U, 0U, 0U},
+    // x = 0x1.73cp-6, expf16(x) = 0x1.05cp+0 (RZ)
+    {0x25cfU, 0x3c17U, 1U, 0U, 0U},
+}};
+
+static constexpr fputil::ExceptValues<float16, 3> EXPF16_EXCEPTS_HI = {{
+    // (input, RZ output, RU offset, RD offset, RN offset)
+    // x = 0x1.c34p+0, expf16(x) = 0x1.74cp+2 (RZ)
+    {0x3f0dU, 0x45d3U, 1U, 0U, 1U},
+    // x = -0x1.488p-5, expf16(x) = 0x1.ebcp-1 (RZ)
+    {0xa922U, 0x3bafU, 1U, 0U, 0U},
+    // x = -0x1.55p-5, expf16(x) = 0x1.ebp-1 (RZ)
+    {0xa954U, 0x3bacU, 1U, 0U, 0U},
+}};
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_MATH_EXP_FLOAT16_CONSTANTS_H
diff --git a/libc/src/__support/math/expf16.h b/libc/src/__support/math/expf16.h
new file mode 100644
index 0000000000000..29a8e44d373f5
--- /dev/null
+++ b/libc/src/__support/math/expf16.h
@@ -0,0 +1,116 @@
+//===-- Implementation header for expf16 ------------------------*- 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_EXPF16_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_EXPF16_H
+
+#include "exp_float16_constants.h"
+
+#include "hdr/errno_macros.h"
+#include "src/math/generic/expxf16.h"
+#include "hdr/fenv_macros.h"
+#include "src/__support/common.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/rounding_mode.h"
+#include "src/__support/macros/optimization.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/FPUtil/except_value_utils.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+static constexpr float16 expf16(float16 x) {
+    using FPBits = fputil::FPBits<float16>;
+  FPBits x_bits(x);
+
+  uint16_t x_u = x_bits.uintval();
+  uint16_t x_abs = x_u & 0x7fffU;
+
+  // When 0 < |x| <= 2^(-5), or |x| >= 12, or x is NaN.
+  if (LIBC_UNLIKELY(x_abs <= 0x2800U || x_abs >= 0x4a00U)) {
+    // exp(NaN) = NaN
+    if (x_bits.is_nan()) {
+      if (x_bits.is_signaling_nan()) {
+        fputil::raise_except_if_required(FE_INVALID);
+        return FPBits::quiet_nan().get_val();
+      }
+
+      return x;
+    }
+
+    // When x >= 12.
+    if (x_bits.is_pos() && x_abs >= 0x4a00U) {
+      // exp(+inf) = +inf
+      if (x_bits.is_inf())
+        return FPBits::inf().get_val();
+
+      switch (fputil::quick_get_round()) {
+      case FE_TONEAREST:
+      case FE_UPWARD:
+        fputil::set_errno_if_required(ERANGE);
+        fputil::raise_except_if_required(FE_OVERFLOW);
+        return FPBits::inf().get_val();
+      default:
+        return FPBits::max_normal().get_val();
+      }
+    }
+
+    // When x <= -18.
+    if (x_u >= 0xcc80U) {
+      // exp(-inf) = +0
+      if (x_bits.is_inf())
+        return FPBits::zero().get_val();
+
+      fputil::set_errno_if_required(ERANGE);
+      fputil::raise_except_if_required(FE_UNDERFLOW | FE_INEXACT);
+
+      switch (fputil::quick_get_round()) {
+      case FE_UPWARD:
+        return FPBits::min_subnormal().get_val();
+      default:
+        return FPBits::zero().get_val();
+      }
+    }
+
+    // When 0 < |x| <= 2^(-5).
+    if (x_abs <= 0x2800U && !x_bits.is_zero()) {
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+      if (auto r = EXPF16_EXCEPTS_LO.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
+        return r.value();
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+      float xf = x;
+      // Degree-3 minimax polynomial generated by Sollya with the following
+      // commands:
+      //   > display = hexadecimal;
+      //   > P = fpminimax(expm1(x)/x, 2, [|SG...|], [-2^-5, 2^-5]);
+      //   > 1 + x * P;
+      return fputil::cast<float16>(
+          fputil::polyeval(xf, 0x1p+0f, 0x1p+0f, 0x1.0004p-1f, 0x1.555778p-3f));
+    }
+  }
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+  if (auto r = EXPF16_EXCEPTS_HI.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
+    return r.value();
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+  // exp(x) = exp(hi + mid) * exp(lo)
+  auto [exp_hi_mid, exp_lo] = exp_range_reduction(x);
+  return fputil::cast<float16>(exp_hi_mid * exp_lo);
+}
+
+} // namespace math
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_MATH_EXPF16_H
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index fd1e6c0d648aa..8d15c2879a8bf 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -1332,19 +1332,7 @@ add_entrypoint_object(
   HDRS
     ../expf16.h
   DEPENDS
-    .expxf16
-    libc.hdr.errno_macros
-    libc.hdr.fenv_macros
-    libc.src.__support.CPP.array
-    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.FPUtil.nearest_integer
-    libc.src.__support.FPUtil.polyeval
-    libc.src.__support.FPUtil.rounding_mode
-    libc.src.__support.macros.optimization
+    libc.src.__support.math.expf
 )
 
 add_entrypoint_object(
diff --git a/libc/src/math/generic/expf16.cpp b/libc/src/math/generic/expf16.cpp
index 1af9b3ec9ad6e..ad213e237f021 100644
--- a/libc/src/math/generic/expf16.cpp
+++ b/libc/src/math/generic/expf16.cpp
@@ -7,120 +7,11 @@
 //===----------------------------------------------------------------------===//
 
 #include "src/math/expf16.h"
-#include "expxf16.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/except_value_utils.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"
 
-namespace LIBC_NAMESPACE_DECL {
-
-#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-static constexpr fputil::ExceptValues<float16, 2> EXPF16_EXCEPTS_LO = {{
-    // (input, RZ output, RU offset, RD offset, RN offset)
-    // x = 0x1.de4p-8, expf16(x) = 0x1.01cp+0 (RZ)
-    {0x1f79U, 0x3c07U, 1U, 0U, 0U},
-    // x = 0x1.73cp-6, expf16(x) = 0x1.05cp+0 (RZ)
-    {0x25cfU, 0x3c17U, 1U, 0U, 0U},
-}};
-
-static constexpr fputil::ExceptValues<float16, 3> EXPF16_EXCEPTS_HI = {{
-    // (input, RZ output, RU offset, RD offset, RN offset)
-    // x = 0x1.c34p+0, expf16(x) = 0x1.74cp+2 (RZ)
-    {0x3f0dU, 0x45d3U, 1U, 0U, 1U},
-    // x = -0x1.488p-5, expf16(x) = 0x1.ebcp-1 (RZ)
-    {0xa922U, 0x3bafU, 1U, 0U, 0U},
-    // x = -0x1.55p-5, expf16(x) = 0x1.ebp-1 (RZ)
-    {0xa954U, 0x3bacU, 1U, 0U, 0U},
-}};
-#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-
-LLVM_LIBC_FUNCTION(float16, expf16, (float16 x)) {
-  using FPBits = fputil::FPBits<float16>;
-  FPBits x_bits(x);
-
-  uint16_t x_u = x_bits.uintval();
-  uint16_t x_abs = x_u & 0x7fffU;
-
-  // When 0 < |x| <= 2^(-5), or |x| >= 12, or x is NaN.
-  if (LIBC_UNLIKELY(x_abs <= 0x2800U || x_abs >= 0x4a00U)) {
-    // exp(NaN) = NaN
-    if (x_bits.is_nan()) {
-      if (x_bits.is_signaling_nan()) {
-        fputil::raise_except_if_required(FE_INVALID);
-        return FPBits::quiet_nan().get_val();
-      }
-
-      return x;
-    }
-
-    // When x >= 12.
-    if (x_bits.is_pos() && x_abs >= 0x4a00U) {
-      // exp(+inf) = +inf
-      if (x_bits.is_inf())
-        return FPBits::inf().get_val();
+#include "src/__support/math/expf16.h"
 
-      switch (fputil::quick_get_round()) {
-      case FE_TONEAREST:
-      case FE_UPWARD:
-        fputil::set_errno_if_required(ERANGE);
-        fputil::raise_except_if_required(FE_OVERFLOW);
-        return FPBits::inf().get_val();
-      default:
-        return FPBits::max_normal().get_val();
-      }
-    }
-
-    // When x <= -18.
-    if (x_u >= 0xcc80U) {
-      // exp(-inf) = +0
-      if (x_bits.is_inf())
-        return FPBits::zero().get_val();
-
-      fputil::set_errno_if_required(ERANGE);
-      fputil::raise_except_if_required(FE_UNDERFLOW | FE_INEXACT);
-
-      switch (fputil::quick_get_round()) {
-      case FE_UPWARD:
-        return FPBits::min_subnormal().get_val();
-      default:
-        return FPBits::zero().get_val();
-      }
-    }
-
-    // When 0 < |x| <= 2^(-5).
-    if (x_abs <= 0x2800U && !x_bits.is_zero()) {
-#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-      if (auto r = EXPF16_EXCEPTS_LO.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
-        return r.value();
-#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-
-      float xf = x;
-      // Degree-3 minimax polynomial generated by Sollya with the following
-      // commands:
-      //   > display = hexadecimal;
-      //   > P = fpminimax(expm1(x)/x, 2, [|SG...|], [-2^-5, 2^-5]);
-      //   > 1 + x * P;
-      return fputil::cast<float16>(
-          fputil::polyeval(xf, 0x1p+0f, 0x1p+0f, 0x1.0004p-1f, 0x1.555778p-3f));
-    }
-  }
-
-#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-  if (auto r = EXPF16_EXCEPTS_HI.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
-    return r.value();
-#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+namespace LIBC_NAMESPACE_DECL {
 
-  // exp(x) = exp(hi + mid) * exp(lo)
-  auto [exp_hi_mid, exp_lo] = exp_range_reduction(x);
-  return fputil::cast<float16>(exp_hi_mid * exp_lo);
-}
+LLVM_LIBC_FUNCTION(float16, expf16, (float16 x)) { return math::expf16(x); }
 
 } // namespace LIBC_NAMESPACE_DECL
diff --git a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
index 2484a2f1e2bd7..efba1eb640eb8 100644
--- a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
@@ -2096,6 +2096,34 @@ libc_support_library(
     ],
 )
 
+libc_support_library(
+    name = "__support_math_exp_float16_constants",
+    hdrs = ["src/__support/math/exp_float16_constants.h"],
+    deps = [
+        ":__support_FPUtil_except_value_utils"
+    ],
+)
+
+libc_support_library(
+    name = "__support_math_expf16",
+    hdrs = ["src/__support/math/expf16.h"],
+    deps = [
+        ":__support_common",
+        ":hdr_errno_macros",
+        ":hdr_fenv_macros",
+        ":__support_cpp_array",
+        ":__support_fputil_cast",
+        ":__support_fputil_except_value_utils",
+        ":__support_fputil_fenv_impl",
+        ":__support_fputil_fp_bits",
+        ":__support_fputil_multiply_add",
+        ":__support_fputil_nearest_integer",
+        ":__support_fputil_polyeval",
+        ":__support_fputil_rounding_mode",
+        ":__support_macros_optimization",
+    ],
+)
+
 ############################### complex targets ################################
 
 libc_function(
@@ -2701,6 +2729,7 @@ libc_math_function(
 libc_math_function(
     name = "expf16",
     additional_deps = [
+        ":__support_math_expf16",
         ":expxf16",
     ],
 )

github-actions · 2025-07-08T00:02:30Z

✅ With the latest revision this PR passed the C/C++ code formatter.

[libc][math] Refactor expf16 implementation to header-only in src/__s…

8a9ca87

…upport/math folder.

bassiounix requested review from aaronmondal, keith and rupprecht as code owners July 8, 2025 00:00

llvmbot added libc bazel "Peripheral" support tier build system: utils/bazel labels Jul 8, 2025

bassiounix mentioned this pull request Jul 7, 2025

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

Closed

bassiounix added 2 commits July 8, 2025 03:11

fix code style

b22f973

fix dependency

d48dbb5

bassiounix mentioned this pull request Jul 8, 2025

[libc][math] Refactor frexpf128 implementation to header-only in src/__support/math folder. #147450

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lntue reviewed Jul 8, 2025

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Comment thread libc/src/__support/math/exp_float16_constants.h Outdated

bassiounix added 2 commits July 8, 2025 19:09

Remove expf16_constants.h

8437b69

remove LIBC_INLINE

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bassiounix requested a review from lntue July 8, 2025 16:23

lntue reviewed Jul 9, 2025

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Comment thread libc/src/__support/math/expf16.h

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apply requested changes

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bassiounix requested a review from lntue July 9, 2025 19:48

bassiounix added 3 commits July 9, 2025 22:48

fix styles

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fix type check

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redo f16 checks

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lntue approved these changes Jul 10, 2025

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lntue merged commit c25a5e0 into llvm:main Jul 11, 2025
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[libc][math] Refactor expf16 implementation to header-only in src/__support/math folder.#147428

[libc][math] Refactor expf16 implementation to header-only in src/__support/math folder.#147428
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