[libc-commits] [libc] [llvm] [libc][math] Refactor tanhf16 implementation to header-only in src/__support/math folder. (PR #178645)
Xinlong Chen via libc-commits
libc-commits at lists.llvm.org
Thu Jan 29 04:10:09 PST 2026
https://github.com/Xinlong-Chen updated https://github.com/llvm/llvm-project/pull/178645
>From 1c00018096005d4457e616080274d93da75b6439 Mon Sep 17 00:00:00 2001
From: xinlongchen <xinlongchen at tencent.com>
Date: Thu, 29 Jan 2026 20:05:30 +0800
Subject: [PATCH] [libc][math] Refactor tanhf16 implementation to header-only
in src/__support/math folder.
---
libc/shared/math.h | 1 +
libc/shared/math/tanhf16.h | 23 +++
libc/src/__support/math/CMakeLists.txt | 19 ++
libc/src/__support/math/tanhf16.h | 163 ++++++++++++++++++
libc/src/math/generic/CMakeLists.txt | 12 +-
libc/src/math/generic/tanhf16.cpp | 140 +--------------
libc/test/shared/CMakeLists.txt | 1 +
libc/test/shared/shared_math_test.cpp | 1 +
.../llvm-project-overlay/libc/BUILD.bazel | 10 +-
9 files changed, 220 insertions(+), 150 deletions(-)
create mode 100644 libc/shared/math/tanhf16.h
create mode 100644 libc/src/__support/math/tanhf16.h
diff --git a/libc/shared/math.h b/libc/shared/math.h
index 6b1f94fc6cce5..e9e0938ba1ba3 100644
--- a/libc/shared/math.h
+++ b/libc/shared/math.h
@@ -102,5 +102,6 @@
#include "math/sqrtf16.h"
#include "math/tan.h"
#include "math/tanf.h"
+#include "math/tanhf16.h"
#endif // LLVM_LIBC_SHARED_MATH_H
diff --git a/libc/shared/math/tanhf16.h b/libc/shared/math/tanhf16.h
new file mode 100644
index 0000000000000..47f3531d94ee1
--- /dev/null
+++ b/libc/shared/math/tanhf16.h
@@ -0,0 +1,23 @@
+//===-- Shared tanhf16 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_TANHF16_H
+#define LLVM_LIBC_SHARED_MATH_TANHF16_H
+
+#include "shared/libc_common.h"
+#include "src/__support/math/tanhf16.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace shared {
+
+using math::tanhf16;
+
+} // namespace shared
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SHARED_MATH_TANHF16_H
diff --git a/libc/src/__support/math/CMakeLists.txt b/libc/src/__support/math/CMakeLists.txt
index aad2270340c66..1893eeac13b1d 100644
--- a/libc/src/__support/math/CMakeLists.txt
+++ b/libc/src/__support/math/CMakeLists.txt
@@ -1487,3 +1487,22 @@ add_header_library(
libc.src.__support.FPUtil.polyeval
libc.src.__support.macros.optimization
)
+
+add_header_library(
+ tanhf16
+ HDRS
+ tanhf16.h
+ DEPENDS
+ 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.expxf16_utils
+)
diff --git a/libc/src/__support/math/tanhf16.h b/libc/src/__support/math/tanhf16.h
new file mode 100644
index 0000000000000..4983092e004b1
--- /dev/null
+++ b/libc/src/__support/math/tanhf16.h
@@ -0,0 +1,163 @@
+//===-- Single-precision tanhf16 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_TANHF16_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_TANHF16_H
+
+#include "hdr/fenv_macros.h"
+#include "src/__support/CPP/array.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/multiply_add.h"
+#include "src/__support/FPUtil/nearest_integer.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"
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+namespace tanhf16_internal {
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+static constexpr fputil::ExceptValues<float16, 2> TANHF16_EXCEPTS = {{
+ // x = 0x1.f54p+0, tanhf16(x) = 0x1.ecp-1 (RZ)
+ {0x3fd5U, 0x3bb0U, 1U, 0U, 0U},
+ // x = -0x1.f54p+0, tanhf16(x) = -0x1.ecp-1 (RZ)
+ {0xbfd5U, 0xbbb0U, 0U, 1U, 0U},
+}};
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+} // namespace tanhf16_internal
+
+LIBC_INLINE static constexpr float16 tanhf16(float16 x) {
+ using namespace tanhf16_internal;
+ 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 -2^(-14) <= x <= -2^(-9), or |x| <= 0x1.d2p-4,
+ // or |x| >= atanh(1 - 2^(-11)), or x is NaN.
+ if (LIBC_UNLIKELY(x_abs <= 0x2f48U || x_abs >= 0x4429U)) {
+ // tanh(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 -2^(-14) <= x <= -2^(-9).
+ if (x_u >= 0x8400U && x_u <= 0x9800U) {
+ switch (fputil::quick_get_round()) {
+ case FE_TONEAREST:
+ case FE_DOWNWARD:
+ return x;
+ default:
+ return FPBits(static_cast<uint16_t>(x_u - 1U)).get_val();
+ }
+ }
+
+ // When |x| <= 0x1.d2p-4.
+ if (x_abs <= 0x2f48U) {
+ if (LIBC_UNLIKELY(x_abs == 0))
+ return x;
+
+ float xf = x;
+ float xf_sq = xf * xf;
+ // Degree-7 Taylor expansion generated by Sollya with the following
+ // commands:
+ // > taylor(tanh(x), 7, 0);
+ // > display = hexadecimal;
+ // > // For each coefficient:
+ // > round(/* put coefficient here */, SG, RN);
+ return fputil::cast<float16>(
+ xf * fputil::polyeval(xf_sq, 0x1p+0f, -0x1.555556p-2f, 0x1.111112p-3f,
+ -0x1.ba1ba2p-5f));
+ }
+
+ // tanh(+/-inf) = +/-1
+ if (x_bits.is_inf())
+ return FPBits::one(x_bits.sign()).get_val();
+
+ // When |x| >= atanh(1 - 2^(-11)).
+ fputil::raise_except_if_required(FE_INEXACT);
+
+ int rounding_mode = fputil::quick_get_round();
+ if ((rounding_mode == FE_TONEAREST && x_abs >= 0x4482U) ||
+ (rounding_mode == FE_UPWARD && x_bits.is_pos()) ||
+ (rounding_mode == FE_DOWNWARD && x_bits.is_neg())) {
+ return FPBits::one(x_bits.sign()).get_val();
+ }
+ if (x_bits.is_pos())
+ return fputil::cast<float16>(0x1.ffcp-1);
+ return fputil::cast<float16>(-0x1.ffcp-1);
+ }
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+ if (auto r = TANHF16_EXCEPTS.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
+ return r.value();
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+ // For atanh(-1 + 2^(-11)) < x < atanh(1 - 2^(-11)), to compute tanh(x), we
+ // perform the following range reduction: find hi, mid, lo, such that:
+ // x = (hi + mid) * log(2) * 0.5 + lo, in which
+ // hi is an integer,
+ // mid * 2^5 is an integer,
+ // -2^(-5) <= lo < 2^(-5).
+ // In particular,
+ // hi + mid = round(x * log2(e) * 2 * 2^5) * 2^(-5).
+ // Then,
+ // tanh(x) = sinh(x)/cosh(x)
+ // = (e^x - e^(-x)) / (e^x + e^(-x))
+ // = (e^(2x) - 1) / (e^(2x) + 1)
+ // = (2^(hi + mid) * e^(2*lo) - 1) / (2^(hi + mid) * e^(2*lo) + 1)
+ // = (e^(2*lo) - 2^(-hi - mid)) / (e^(2*lo) + 2^(-hi - mid))
+ // We store 2^(-mid) in the lookup table EXP2_MID_5_BITS, and compute
+ // 2^(-hi - mid) by adding -hi to the exponent field of 2^(-mid).
+ // e^lo is computed using a degree-3 minimax polynomial generated by Sollya.
+
+ float xf = x;
+ float kf = fputil::nearest_integer(xf * (LOG2F_E * 2.0f * 0x1.0p+5f));
+ int x_hi_mid = -static_cast<int>(kf);
+ unsigned x_hi = static_cast<unsigned>(x_hi_mid) >> 5;
+ unsigned x_mid = static_cast<unsigned>(x_hi_mid) & 0x1f;
+ // lo = x - (hi + mid)
+ // = round(x * log2(e) * 2 * 2^5) * log(2) * 0.5 * (-2^(-5)) + x
+ float lo = fputil::multiply_add(kf, LOGF_2 * 0.5f * -0x1.0p-5f, xf);
+
+ uint32_t exp2_hi_mid_bits =
+ EXP2_MID_5_BITS[x_mid] +
+ static_cast<uint32_t>(x_hi << fputil::FPBits<float>::FRACTION_LEN);
+ // exp2_hi_mid = 2^(-hi - mid)
+ float exp2_hi_mid = fputil::FPBits<float>(exp2_hi_mid_bits).get_val();
+ // Degree-3 minimax polynomial generated by Sollya with the following
+ // commands:
+ // > display = hexadecimal;
+ // > P = fpminimax(expm1(2*x)/x, 2, [|SG...|], [-2^-5, 2^-5]);
+ // > 1 + x * P;
+ float exp_2lo =
+ fputil::polyeval(lo, 0x1p+0f, 0x1p+1f, 0x1.001p+1f, 0x1.555ddep+0f);
+ return fputil::cast<float16>((exp_2lo - exp2_hi_mid) /
+ (exp_2lo + exp2_hi_mid));
+}
+
+} // namespace math
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_MATH_TANHF16_H
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index 21c3a861c87d7..ab7e0f3509fcf 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -4141,17 +4141,7 @@ add_entrypoint_object(
../tanhf16.h
DEPENDS
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.expxf16_utils
+ libc.src.__support.math.tanhf16
)
add_entrypoint_object(
diff --git a/libc/src/math/generic/tanhf16.cpp b/libc/src/math/generic/tanhf16.cpp
index fc0e28b95a834..564f37c79d308 100644
--- a/libc/src/math/generic/tanhf16.cpp
+++ b/libc/src/math/generic/tanhf16.cpp
@@ -7,146 +7,10 @@
//===----------------------------------------------------------------------===//
#include "src/math/tanhf16.h"
-#include "hdr/fenv_macros.h"
-#include "src/__support/CPP/array.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/multiply_add.h"
-#include "src/__support/FPUtil/nearest_integer.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/tanhf16.h"
namespace LIBC_NAMESPACE_DECL {
-#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-static constexpr fputil::ExceptValues<float16, 2> TANHF16_EXCEPTS = {{
- // x = 0x1.f54p+0, tanhf16(x) = 0x1.ecp-1 (RZ)
- {0x3fd5U, 0x3bb0U, 1U, 0U, 0U},
- // x = -0x1.f54p+0, tanhf16(x) = -0x1.ecp-1 (RZ)
- {0xbfd5U, 0xbbb0U, 0U, 1U, 0U},
-}};
-#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-
-LLVM_LIBC_FUNCTION(float16, tanhf16, (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 -2^(-14) <= x <= -2^(-9), or |x| <= 0x1.d2p-4,
- // or |x| >= atanh(1 - 2^(-11)), or x is NaN.
- if (LIBC_UNLIKELY(x_abs <= 0x2f48U || x_abs >= 0x4429U)) {
- // tanh(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 -2^(-14) <= x <= -2^(-9).
- if (x_u >= 0x8400U && x_u <= 0x9800U) {
- switch (fputil::quick_get_round()) {
- case FE_TONEAREST:
- case FE_DOWNWARD:
- return x;
- default:
- return FPBits(static_cast<uint16_t>(x_u - 1U)).get_val();
- }
- }
-
- // When |x| <= 0x1.d2p-4.
- if (x_abs <= 0x2f48U) {
- if (LIBC_UNLIKELY(x_abs == 0))
- return x;
-
- float xf = x;
- float xf_sq = xf * xf;
- // Degree-7 Taylor expansion generated by Sollya with the following
- // commands:
- // > taylor(tanh(x), 7, 0);
- // > display = hexadecimal;
- // > // For each coefficient:
- // > round(/* put coefficient here */, SG, RN);
- return fputil::cast<float16>(
- xf * fputil::polyeval(xf_sq, 0x1p+0f, -0x1.555556p-2f, 0x1.111112p-3f,
- -0x1.ba1ba2p-5f));
- }
-
- // tanh(+/-inf) = +/-1
- if (x_bits.is_inf())
- return FPBits::one(x_bits.sign()).get_val();
-
- // When |x| >= atanh(1 - 2^(-11)).
- fputil::raise_except_if_required(FE_INEXACT);
-
- int rounding_mode = fputil::quick_get_round();
- if ((rounding_mode == FE_TONEAREST && x_abs >= 0x4482U) ||
- (rounding_mode == FE_UPWARD && x_bits.is_pos()) ||
- (rounding_mode == FE_DOWNWARD && x_bits.is_neg())) {
- return FPBits::one(x_bits.sign()).get_val();
- }
- if (x_bits.is_pos())
- return fputil::cast<float16>(0x1.ffcp-1);
- return fputil::cast<float16>(-0x1.ffcp-1);
- }
-
-#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
- if (auto r = TANHF16_EXCEPTS.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
- return r.value();
-#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-
- // For atanh(-1 + 2^(-11)) < x < atanh(1 - 2^(-11)), to compute tanh(x), we
- // perform the following range reduction: find hi, mid, lo, such that:
- // x = (hi + mid) * log(2) * 0.5 + lo, in which
- // hi is an integer,
- // mid * 2^5 is an integer,
- // -2^(-5) <= lo < 2^(-5).
- // In particular,
- // hi + mid = round(x * log2(e) * 2 * 2^5) * 2^(-5).
- // Then,
- // tanh(x) = sinh(x)/cosh(x)
- // = (e^x - e^(-x)) / (e^x + e^(-x))
- // = (e^(2x) - 1) / (e^(2x) + 1)
- // = (2^(hi + mid) * e^(2*lo) - 1) / (2^(hi + mid) * e^(2*lo) + 1)
- // = (e^(2*lo) - 2^(-hi - mid)) / (e^(2*lo) + 2^(-hi - mid))
- // We store 2^(-mid) in the lookup table EXP2_MID_5_BITS, and compute
- // 2^(-hi - mid) by adding -hi to the exponent field of 2^(-mid).
- // e^lo is computed using a degree-3 minimax polynomial generated by Sollya.
-
- float xf = x;
- float kf = fputil::nearest_integer(xf * (LOG2F_E * 2.0f * 0x1.0p+5f));
- int x_hi_mid = -static_cast<int>(kf);
- unsigned x_hi = static_cast<unsigned>(x_hi_mid) >> 5;
- unsigned x_mid = static_cast<unsigned>(x_hi_mid) & 0x1f;
- // lo = x - (hi + mid)
- // = round(x * log2(e) * 2 * 2^5) * log(2) * 0.5 * (-2^(-5)) + x
- float lo = fputil::multiply_add(kf, LOGF_2 * 0.5f * -0x1.0p-5f, xf);
-
- uint32_t exp2_hi_mid_bits =
- EXP2_MID_5_BITS[x_mid] +
- static_cast<uint32_t>(x_hi << fputil::FPBits<float>::FRACTION_LEN);
- // exp2_hi_mid = 2^(-hi - mid)
- float exp2_hi_mid = fputil::FPBits<float>(exp2_hi_mid_bits).get_val();
- // Degree-3 minimax polynomial generated by Sollya with the following
- // commands:
- // > display = hexadecimal;
- // > P = fpminimax(expm1(2*x)/x, 2, [|SG...|], [-2^-5, 2^-5]);
- // > 1 + x * P;
- float exp_2lo =
- fputil::polyeval(lo, 0x1p+0f, 0x1p+1f, 0x1.001p+1f, 0x1.555ddep+0f);
- return fputil::cast<float16>((exp_2lo - exp2_hi_mid) /
- (exp_2lo + exp2_hi_mid));
-}
+LLVM_LIBC_FUNCTION(float16, tanhf16, (float16 x)) { return math::tanhf16(x);}
} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/test/shared/CMakeLists.txt b/libc/test/shared/CMakeLists.txt
index b0a5ad730cbb2..98f7909547fa6 100644
--- a/libc/test/shared/CMakeLists.txt
+++ b/libc/test/shared/CMakeLists.txt
@@ -99,4 +99,5 @@ add_fp_unittest(
libc.src.__support.math.sqrt
libc.src.__support.math.tan
libc.src.__support.math.tanf
+ libc.src.__support.math.tanhf16
)
diff --git a/libc/test/shared/shared_math_test.cpp b/libc/test/shared/shared_math_test.cpp
index a21863e23c3f9..cce8be020bf91 100644
--- a/libc/test/shared/shared_math_test.cpp
+++ b/libc/test/shared/shared_math_test.cpp
@@ -100,6 +100,7 @@ TEST(LlvmLibcSharedMathTest, AllFloat) {
EXPECT_FP_EQ(0x0p+0f, LIBC_NAMESPACE::shared::sinpif(0.0f));
EXPECT_FP_EQ(0.0f, LIBC_NAMESPACE::shared::sinf(0.0f));
EXPECT_FP_EQ(0.0f, LIBC_NAMESPACE::shared::tanf(0.0f));
+ EXPECT_FP_EQ(0.0f, LIBC_NAMESPACE::shared::tanhf16(0.0f16));
}
TEST(LlvmLibcSharedMathTest, AllDouble) {
diff --git a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
index a313ba48889d8..85f472b6aabdd 100644
--- a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
@@ -3710,6 +3710,14 @@ libc_support_library(
],
)
+libc_support_library(
+ name = "__support_math_tanhf16",
+ hdrs = ["src/__support/math/tanhf16.h"],
+ deps = [
+ ":__support_math_expxf16_utils",
+ ],
+)
+
############################### complex targets ################################
libc_function(
@@ -5420,7 +5428,7 @@ libc_math_function(
libc_math_function(
name = "tanhf16",
additional_deps = [
- ":__support_math_expxf16_utils",
+ ":__support_math_tanhf16",
],
)
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