[libc][math] Refactor exp2f16 implementation to header-only in src/__support/math folder.

[bassiounix]

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

[llvmbot]

@llvm/pr-subscribers-libc

Author: Muhammad Bassiouni (bassiounix)

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/161993.diff

9 Files Affected:

• (modified) libc/shared/math.h (+1)
• (added) libc/shared/math/exp2f16.h (+29)
• (modified) libc/src/__support/math/CMakeLists.txt (+14)
• (added) libc/src/__support/math/exp2f16.h (+111)
• (modified) libc/src/math/generic/CMakeLists.txt (+1-9)
• (modified) libc/src/math/generic/exp2f16.cpp (+2-84)
• (modified) libc/test/shared/CMakeLists.txt (+1)
• (modified) libc/test/shared/shared_math_test.cpp (+1-1)
• (modified) utils/bazel/llvm-project-overlay/libc/BUILD.bazel (+17-1)

diff --git a/libc/shared/math.h b/libc/shared/math.h
index 1262fa6f682d0..8bff70f1c5336 100644
--- a/libc/shared/math.h
+++ b/libc/shared/math.h
@@ -49,6 +49,7 @@
 #include "math/exp10m1f16.h"
 #include "math/exp2.h"
 #include "math/exp2f.h"
+#include "math/exp2f16.h"
 #include "math/expf.h"
 #include "math/expf16.h"
 #include "math/frexpf.h"
diff --git a/libc/shared/math/exp2f16.h b/libc/shared/math/exp2f16.h
new file mode 100644
index 0000000000000..f799511efb0d7
--- /dev/null
+++ b/libc/shared/math/exp2f16.h
@@ -0,0 +1,29 @@
+//===-- Shared exp2f16 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_EXP2F16_H
+#define LLVM_LIBC_SHARED_MATH_EXP2F16_H
+
+#include "include/llvm-libc-macros/float16-macros.h"
+#include "shared/libc_common.h"
+
+#ifdef LIBC_TYPES_HAS_FLOAT16
+
+#include "src/__support/math/exp2f16.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace shared {
+
+using math::exp2f16;
+
+} // namespace shared
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_TYPES_HAS_FLOAT16
+
+#endif // LLVM_LIBC_SHARED_MATH_EXP2F16_H
diff --git a/libc/src/__support/math/CMakeLists.txt b/libc/src/__support/math/CMakeLists.txt
index 203ebb4bf1760..185900efa7354 100644
--- a/libc/src/__support/math/CMakeLists.txt
+++ b/libc/src/__support/math/CMakeLists.txt
@@ -753,6 +753,20 @@ add_header_library(
     libc.src.errno.errno
 )
 
+add_header_library(
+  exp2f16
+  HDRS
+    exp2f16.h
+  DEPENDS
+    .expxf16_utils
+    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.rounding_mode
+    libc.src.__support.macros.optimization
+)
+
 add_header_library(
   exp10
   HDRS
diff --git a/libc/src/__support/math/exp2f16.h b/libc/src/__support/math/exp2f16.h
new file mode 100644
index 0000000000000..599ba0f5411bd
--- /dev/null
+++ b/libc/src/__support/math/exp2f16.h
@@ -0,0 +1,111 @@
+//===-- Implementation header for exp2f16 -----------------------*- 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_EXP2F16_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_EXP2F16_H
+
+#include "include/llvm-libc-macros/float16-macros.h"
+
+#ifdef LIBC_TYPES_HAS_FLOAT16
+
+#include "expxf16_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/rounding_mode.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+LIBC_INLINE static constexpr float16 exp2f16(float16 x) {
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+  constexpr fputil::ExceptValues<float16, 3> EXP2F16_EXCEPTS = {{
+      // (input, RZ output, RU offset, RD offset, RN offset)
+      // x = 0x1.714p-11, exp2f16(x) = 0x1p+0 (RZ)
+      {0x11c5U, 0x3c00U, 1U, 0U, 1U},
+      // x = -0x1.558p-4, exp2f16(x) = 0x1.e34p-1 (RZ)
+      {0xad56U, 0x3b8dU, 1U, 0U, 0U},
+      // x = -0x1.d5cp-4, exp2f16(x) = 0x1.d8cp-1 (RZ)
+      {0xaf57U, 0x3b63U, 1U, 0U, 0U},
+  }};
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+  using namespace math::expxf16_internal;
+  using FPBits = fputil::FPBits<float16>;
+  FPBits x_bits(x);
+
+  uint16_t x_u = x_bits.uintval();
+  uint16_t x_abs = x_u & 0x7fffU;
+
+  // When |x| >= 16, or x is NaN.
+  if (LIBC_UNLIKELY(x_abs >= 0x4c00U)) {
+    // exp2(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 >= 16.
+    if (x_bits.is_pos()) {
+      // exp2(+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 <= -25.
+    if (x_u >= 0xce40U) {
+      // exp2(-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);
+
+      if (fputil::fenv_is_round_up())
+        return FPBits::min_subnormal().get_val();
+      return FPBits::zero().get_val();
+    }
+  }
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+  if (auto r = EXP2F16_EXCEPTS.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
+    return r.value();
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+  // exp2(x) = exp2(hi + mid) * exp2(lo)
+  auto [exp2_hi_mid, exp2_lo] = exp2_range_reduction(x);
+  return fputil::cast<float16>(exp2_hi_mid * exp2_lo);
+}
+
+} // namespace math
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_TYPES_HAS_FLOAT16
+
+#endif // LLVM_LIBC_SRC___SUPPORT_MATH_EXP2F16_H
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index 5738fe86f6c7b..8e969de5a8031 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -1468,15 +1468,7 @@ add_entrypoint_object(
   HDRS
     ../exp2f16.h
   DEPENDS
-    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.rounding_mode
-    libc.src.__support.macros.optimization
-    libc.src.__support.math.expxf16_utils
+    libc.src.__support.math.exp2f16
 )
 
 add_entrypoint_object(
diff --git a/libc/src/math/generic/exp2f16.cpp b/libc/src/math/generic/exp2f16.cpp
index 5db0c3a9de08d..80799d49c20c1 100644
--- a/libc/src/math/generic/exp2f16.cpp
+++ b/libc/src/math/generic/exp2f16.cpp
@@ -7,92 +7,10 @@
 //===----------------------------------------------------------------------===//
 
 #include "src/math/exp2f16.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/rounding_mode.h"
-#include "src/__support/common.h"
-#include "src/__support/macros/config.h"
-#include "src/__support/macros/optimization.h"
-#include "src/__support/math/expxf16_utils.h"
+#include "src/__support/math/exp2f16.h"
 
 namespace LIBC_NAMESPACE_DECL {
 
-#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-static constexpr fputil::ExceptValues<float16, 3> EXP2F16_EXCEPTS = {{
-    // (input, RZ output, RU offset, RD offset, RN offset)
-    // x = 0x1.714p-11, exp2f16(x) = 0x1p+0 (RZ)
-    {0x11c5U, 0x3c00U, 1U, 0U, 1U},
-    // x = -0x1.558p-4, exp2f16(x) = 0x1.e34p-1 (RZ)
-    {0xad56U, 0x3b8dU, 1U, 0U, 0U},
-    // x = -0x1.d5cp-4, exp2f16(x) = 0x1.d8cp-1 (RZ)
-    {0xaf57U, 0x3b63U, 1U, 0U, 0U},
-}};
-#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-
-LLVM_LIBC_FUNCTION(float16, exp2f16, (float16 x)) {
-  using namespace math::expxf16_internal;
-  using FPBits = fputil::FPBits<float16>;
-  FPBits x_bits(x);
-
-  uint16_t x_u = x_bits.uintval();
-  uint16_t x_abs = x_u & 0x7fffU;
-
-  // When |x| >= 16, or x is NaN.
-  if (LIBC_UNLIKELY(x_abs >= 0x4c00U)) {
-    // exp2(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 >= 16.
-    if (x_bits.is_pos()) {
-      // exp2(+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 <= -25.
-    if (x_u >= 0xce40U) {
-      // exp2(-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);
-
-      if (fputil::fenv_is_round_up())
-        return FPBits::min_subnormal().get_val();
-      return FPBits::zero().get_val();
-    }
-  }
-
-#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-  if (auto r = EXP2F16_EXCEPTS.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
-    return r.value();
-#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-
-  // exp2(x) = exp2(hi + mid) * exp2(lo)
-  auto [exp2_hi_mid, exp2_lo] = exp2_range_reduction(x);
-  return fputil::cast<float16>(exp2_hi_mid * exp2_lo);
-}
+LLVM_LIBC_FUNCTION(float16, exp2f16, (float16 x)) { return math::exp2f16(x); }
 
 } // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/test/shared/CMakeLists.txt b/libc/test/shared/CMakeLists.txt
index dbc3889c76471..685b954c1f306 100644
--- a/libc/test/shared/CMakeLists.txt
+++ b/libc/test/shared/CMakeLists.txt
@@ -42,6 +42,7 @@ add_fp_unittest(
     libc.src.__support.math.exp
     libc.src.__support.math.exp2
     libc.src.__support.math.exp2f
+    libc.src.__support.math.exp2f16
     libc.src.__support.math.exp10
     libc.src.__support.math.exp10f
     libc.src.__support.math.exp10f16
diff --git a/libc/test/shared/shared_math_test.cpp b/libc/test/shared/shared_math_test.cpp
index d118d96da69dd..b114eefccbf77 100644
--- a/libc/test/shared/shared_math_test.cpp
+++ b/libc/test/shared/shared_math_test.cpp
@@ -28,7 +28,7 @@ TEST(LlvmLibcSharedMathTest, AllFloat16) {
   EXPECT_FP_EQ(0x1p+0f16, LIBC_NAMESPACE::shared::cospif16(0.0f16));
   EXPECT_FP_EQ(0x1p+0f16, LIBC_NAMESPACE::shared::exp10f16(0.0f16));
   EXPECT_FP_EQ(0x0p+0f16, LIBC_NAMESPACE::shared::exp10m1f16(0.0f16));
-
+  EXPECT_FP_EQ(0x1p+0f16, LIBC_NAMESPACE::shared::exp2f16(0.0f16));
   EXPECT_FP_EQ(0x1p+0f16, LIBC_NAMESPACE::shared::expf16(0.0f16));
 
   ASSERT_FP_EQ(float16(8 << 5), LIBC_NAMESPACE::shared::ldexpf16(8.0f16, 5));
diff --git a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
index 00db514beaf34..d47e5feb7eff8 100644
--- a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
@@ -2895,6 +2895,22 @@ libc_support_library(
     ],
 )
 
+libc_support_library(
+    name = "__support_math_exp2f16",
+    hdrs = ["src/__support/math/exp2f16.h"],
+    deps = [
+        ":__support_fputil_except_value_utils",
+        ":__support_fputil_fma",
+        ":__support_fputil_multiply_add",
+        ":__support_fputil_nearest_integer",
+        ":__support_fputil_polyeval",
+        ":__support_fputil_rounding_mode",
+        ":__support_macros_optimization",
+        ":__support_math_common_constants",
+        ":__support_math_expxf16_utils",
+    ],
+)
+
 libc_support_library(
     name = "__support_math_exp10",
     hdrs = ["src/__support/math/exp10.h"],
@@ -3683,7 +3699,7 @@ libc_math_function(
 libc_math_function(
     name = "exp2f16",
     additional_deps = [
-        ":__support_math_expxf16_utils",
+        ":__support_math_exp2f16",
     ],
 )
 

[bassiounix]

Merge activity

• Oct 11, 8:25 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Oct 11, 8:27 PM UTC: @bassiounix merged this pull request with Graphite.