[libc][math] Refactor expf implementation to header-only in src/__support/math folder. #143790

lntue · 2025-06-11T21:39:56Z

This is a step 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

…port/math folder.

llvmbot · 2025-06-11T21:40:28Z

@llvm/pr-subscribers-libc

Author: None (lntue)

Changes

This is a step 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

Patch is 21.44 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/143790.diff

9 Files Affected:

(added) libc/shared/math.h (+23)
(modified) libc/src/__support/CMakeLists.txt (+2)
(added) libc/src/__support/math/CMakeLists.txt (+24)
(added) libc/src/__support/math/exp_float_constants.h (+145)
(added) libc/src/__support/math/expf.h (+116)
(modified) libc/src/math/generic/CMakeLists.txt (+1-9)
(modified) libc/src/math/generic/expf.cpp (+2-95)
(modified) utils/bazel/llvm-project-overlay/libc/BUILD.bazel (+4)
(modified) utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl (+2-1)

diff --git a/libc/shared/math.h b/libc/shared/math.h
new file mode 100644
index 0000000000000..68b05bbced2c0
--- /dev/null
+++ b/libc/shared/math.h
@@ -0,0 +1,23 @@
+//===-- Floating point math 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_SHARED_MATH_H
+#define LLVM_LIBC_SHARED_MATH_H
+
+#include "libc_common.h"
+#include "src/__support/math/expf.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace shared {
+
+using math::expf;
+
+} // namespace shared
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SHARED_FP_BITS_H
diff --git a/libc/src/__support/CMakeLists.txt b/libc/src/__support/CMakeLists.txt
index 327ff5e0c6a37..8cf2b0cdcdccc 100644
--- a/libc/src/__support/CMakeLists.txt
+++ b/libc/src/__support/CMakeLists.txt
@@ -390,3 +390,5 @@ add_subdirectory(HashTable)
 add_subdirectory(fixed_point)
 
 add_subdirectory(time)
+
+add_subdirectory(math)
diff --git a/libc/src/__support/math/CMakeLists.txt b/libc/src/__support/math/CMakeLists.txt
new file mode 100644
index 0000000000000..66c1d19a1cab0
--- /dev/null
+++ b/libc/src/__support/math/CMakeLists.txt
@@ -0,0 +1,24 @@
+add_header_library(
+  exp_float_constants
+  HDRS
+    exp_float_constants.h
+  DEPENDS
+    libc.src.__support.macros.config
+)
+
+add_header_library(
+  expf
+  HDRS
+    expf.h
+  DEPENDS
+    .exp_float_constants
+    libc.src.__support.common
+    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.config
+    libc.src.__support.macros.optimization
+)
diff --git a/libc/src/__support/math/exp_float_constants.h b/libc/src/__support/math/exp_float_constants.h
new file mode 100644
index 0000000000000..cabb227a034b5
--- /dev/null
+++ b/libc/src/__support/math/exp_float_constants.h
@@ -0,0 +1,145 @@
+//===-- Look-up tables for exp*f 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_FLOAT_CONSTANTS_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_EXP_FLOAT_CONSTANTS_H
+
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+// Lookup table for exp(m) with m = -104, ..., 89.
+//   -104 = floor(log(single precision's min denormal))
+//     89 = ceil(log(single precision's max normal))
+// Table is generated with Sollya as follow:
+// > display = hexadecimal;
+// > for i from -104 to 89 do { D(exp(i)); };
+static constexpr double EXP_M1[195] = {
+    0x1.f1e6b68529e33p-151, 0x1.525be4e4e601dp-149, 0x1.cbe0a45f75eb1p-148,
+    0x1.3884e838aea68p-146, 0x1.a8c1f14e2af5dp-145, 0x1.20a717e64a9bdp-143,
+    0x1.8851d84118908p-142, 0x1.0a9bdfb02d240p-140, 0x1.6a5bea046b42ep-139,
+    0x1.ec7f3b269efa8p-138, 0x1.4eafb87eab0f2p-136, 0x1.c6e2d05bbc000p-135,
+    0x1.35208867c2683p-133, 0x1.a425b317eeacdp-132, 0x1.1d8508fa8246ap-130,
+    0x1.840fbc08fdc8ap-129, 0x1.07b7112bc1ffep-127, 0x1.666d0dad2961dp-126,
+    0x1.e726c3f64d0fep-125, 0x1.4b0dc07cabf98p-123, 0x1.c1f2daf3b6a46p-122,
+    0x1.31c5957a47de2p-120, 0x1.9f96445648b9fp-119, 0x1.1a6baeadb4fd1p-117,
+    0x1.7fd974d372e45p-116, 0x1.04da4d1452919p-114, 0x1.62891f06b3450p-113,
+    0x1.e1dd273aa8a4ap-112, 0x1.4775e0840bfddp-110, 0x1.bd109d9d94bdap-109,
+    0x1.2e73f53fba844p-107, 0x1.9b138170d6bfep-106, 0x1.175af0cf60ec5p-104,
+    0x1.7baee1bffa80bp-103, 0x1.02057d1245cebp-101, 0x1.5eafffb34ba31p-100,
+    0x1.dca23bae16424p-99,  0x1.43e7fc88b8056p-97,  0x1.b83bf23a9a9ebp-96,
+    0x1.2b2b8dd05b318p-94,  0x1.969d47321e4ccp-93,  0x1.1452b7723aed2p-91,
+    0x1.778fe2497184cp-90,  0x1.fe7116182e9ccp-89,  0x1.5ae191a99585ap-87,
+    0x1.d775d87da854dp-86,  0x1.4063f8cc8bb98p-84,  0x1.b374b315f87c1p-83,
+    0x1.27ec458c65e3cp-81,  0x1.923372c67a074p-80,  0x1.1152eaeb73c08p-78,
+    0x1.737c5645114b5p-77,  0x1.f8e6c24b5592ep-76,  0x1.571db733a9d61p-74,
+    0x1.d257d547e083fp-73,  0x1.3ce9b9de78f85p-71,  0x1.aebabae3a41b5p-70,
+    0x1.24b6031b49bdap-68,  0x1.8dd5e1bb09d7ep-67,  0x1.0e5b73d1ff53dp-65,
+    0x1.6f741de1748ecp-64,  0x1.f36bd37f42f3ep-63,  0x1.536452ee2f75cp-61,
+    0x1.cd480a1b74820p-60,  0x1.39792499b1a24p-58,  0x1.aa0de4bf35b38p-57,
+    0x1.2188ad6ae3303p-55,  0x1.898471fca6055p-54,  0x1.0b6c3afdde064p-52,
+    0x1.6b7719a59f0e0p-51,  0x1.ee001eed62aa0p-50,  0x1.4fb547c775da8p-48,
+    0x1.c8464f7616468p-47,  0x1.36121e24d3bbap-45,  0x1.a56e0c2ac7f75p-44,
+    0x1.1e642baeb84a0p-42,  0x1.853f01d6d53bap-41,  0x1.0885298767e9ap-39,
+    0x1.67852a7007e42p-38,  0x1.e8a37a45fc32ep-37,  0x1.4c1078fe9228ap-35,
+    0x1.c3527e433fab1p-34,  0x1.32b48bf117da2p-32,  0x1.a0db0d0ddb3ecp-31,
+    0x1.1b48655f37267p-29,  0x1.81056ff2c5772p-28,  0x1.05a628c699fa1p-26,
+    0x1.639e3175a689dp-25,  0x1.e355bbaee85cbp-24,  0x1.4875ca227ec38p-22,
+    0x1.be6c6fdb01612p-21,  0x1.2f6053b981d98p-19,  0x1.9c54c3b43bc8bp-18,
+    0x1.18354238f6764p-16,  0x1.7cd79b5647c9bp-15,  0x1.02cf22526545ap-13,
+    0x1.5fc21041027adp-12,  0x1.de16b9c24a98fp-11,  0x1.44e51f113d4d6p-9,
+    0x1.b993fe00d5376p-8,   0x1.2c155b8213cf4p-6,   0x1.97db0ccceb0afp-5,
+    0x1.152aaa3bf81ccp-3,   0x1.78b56362cef38p-2,   0x1.0000000000000p+0,
+    0x1.5bf0a8b145769p+1,   0x1.d8e64b8d4ddaep+2,   0x1.415e5bf6fb106p+4,
+    0x1.b4c902e273a58p+5,   0x1.28d389970338fp+7,   0x1.936dc5690c08fp+8,
+    0x1.122885aaeddaap+10,  0x1.749ea7d470c6ep+11,  0x1.fa7157c470f82p+12,
+    0x1.5829dcf950560p+14,  0x1.d3c4488ee4f7fp+15,  0x1.3de1654d37c9ap+17,
+    0x1.b00b5916ac955p+18,  0x1.259ac48bf05d7p+20,  0x1.8f0ccafad2a87p+21,
+    0x1.0f2ebd0a80020p+23,  0x1.709348c0ea4f9p+24,  0x1.f4f22091940bdp+25,
+    0x1.546d8f9ed26e1p+27,  0x1.ceb088b68e804p+28,  0x1.3a6e1fd9eecfdp+30,
+    0x1.ab5adb9c43600p+31,  0x1.226af33b1fdc1p+33,  0x1.8ab7fb5475fb7p+34,
+    0x1.0c3d3920962c9p+36,  0x1.6c932696a6b5dp+37,  0x1.ef822f7f6731dp+38,
+    0x1.50bba3796379ap+40,  0x1.c9aae4631c056p+41,  0x1.370470aec28edp+43,
+    0x1.a6b765d8cdf6dp+44,  0x1.1f43fcc4b662cp+46,  0x1.866f34a725782p+47,
+    0x1.0953e2f3a1ef7p+49,  0x1.689e221bc8d5bp+50,  0x1.ea215a1d20d76p+51,
+    0x1.4d13fbb1a001ap+53,  0x1.c4b334617cc67p+54,  0x1.33a43d282a519p+56,
+    0x1.a220d397972ebp+57,  0x1.1c25c88df6862p+59,  0x1.8232558201159p+60,
+    0x1.0672a3c9eb871p+62,  0x1.64b41c6d37832p+63,  0x1.e4cf766fe49bep+64,
+    0x1.49767bc0483e3p+66,  0x1.bfc951eb8bb76p+67,  0x1.304d6aeca254bp+69,
+    0x1.9d97010884251p+70,  0x1.19103e4080b45p+72,  0x1.7e013cd114461p+73,
+    0x1.03996528e074cp+75,  0x1.60d4f6fdac731p+76,  0x1.df8c5af17ba3bp+77,
+    0x1.45e3076d61699p+79,  0x1.baed16a6e0da7p+80,  0x1.2cffdfebde1a1p+82,
+    0x1.9919cabefcb69p+83,  0x1.160345c9953e3p+85,  0x1.79dbc9dc53c66p+86,
+    0x1.00c810d464097p+88,  0x1.5d009394c5c27p+89,  0x1.da57de8f107a8p+90,
+    0x1.425982cf597cdp+92,  0x1.b61e5ca3a5e31p+93,  0x1.29bb825dfcf87p+95,
+    0x1.94a90db0d6fe2p+96,  0x1.12fec759586fdp+98,  0x1.75c1dc469e3afp+99,
+    0x1.fbfd219c43b04p+100, 0x1.5936d44e1a146p+102, 0x1.d531d8a7ee79cp+103,
+    0x1.3ed9d24a2d51bp+105, 0x1.b15cfe5b6e17bp+106, 0x1.268038c2c0e00p+108,
+    0x1.9044a73545d48p+109, 0x1.1002ab6218b38p+111, 0x1.71b3540cbf921p+112,
+    0x1.f6799ea9c414ap+113, 0x1.55779b984f3ebp+115, 0x1.d01a210c44aa4p+116,
+    0x1.3b63da8e91210p+118, 0x1.aca8d6b0116b8p+119, 0x1.234de9e0c74e9p+121,
+    0x1.8bec7503ca477p+122, 0x1.0d0eda9796b90p+124, 0x1.6db0118477245p+125,
+    0x1.f1056dc7bf22dp+126, 0x1.51c2cc3433801p+128, 0x1.cb108ffbec164p+129,
+};
+
+// Lookup table for exp(m * 2^(-7)) with m = 0, ..., 127.
+// Table is generated with Sollya as follow:
+// > display = hexadecimal;
+// > for i from 0 to 127 do { D(exp(i / 128)); };
+static constexpr double EXP_M2[128] = {
+    0x1.0000000000000p0, 0x1.0202015600446p0, 0x1.04080ab55de39p0,
+    0x1.06122436410ddp0, 0x1.08205601127edp0, 0x1.0a32a84e9c1f6p0,
+    0x1.0c49236829e8cp0, 0x1.0e63cfa7ab09dp0, 0x1.1082b577d34edp0,
+    0x1.12a5dd543ccc5p0, 0x1.14cd4fc989cd6p0, 0x1.16f9157587069p0,
+    0x1.192937074e0cdp0, 0x1.1b5dbd3f68122p0, 0x1.1d96b0eff0e79p0,
+    0x1.1fd41afcba45ep0, 0x1.2216045b6f5cdp0, 0x1.245c7613b8a9bp0,
+    0x1.26a7793f60164p0, 0x1.28f7170a755fdp0, 0x1.2b4b58b372c79p0,
+    0x1.2da4478b620c7p0, 0x1.3001ecf601af7p0, 0x1.32645269ea829p0,
+    0x1.34cb8170b5835p0, 0x1.373783a722012p0, 0x1.39a862bd3c106p0,
+    0x1.3c1e2876834aap0, 0x1.3e98deaa11dccp0, 0x1.41188f42c3e32p0,
+    0x1.439d443f5f159p0, 0x1.462707b2bac21p0, 0x1.48b5e3c3e8186p0,
+    0x1.4b49e2ae5ac67p0, 0x1.4de30ec211e60p0, 0x1.50817263c13cdp0,
+    0x1.5325180cfacf7p0, 0x1.55ce0a4c58c7cp0, 0x1.587c53c5a7af0p0,
+    0x1.5b2fff3210fd9p0, 0x1.5de9176045ff5p0, 0x1.60a7a734ab0e8p0,
+    0x1.636bb9a983258p0, 0x1.663559cf1bc7cp0, 0x1.690492cbf9433p0,
+    0x1.6bd96fdd034a2p0, 0x1.6eb3fc55b1e76p0, 0x1.719443a03acb9p0,
+    0x1.747a513dbef6ap0, 0x1.776630c678bc1p0, 0x1.7a57ede9ea23ep0,
+    0x1.7d4f946f0ba8dp0, 0x1.804d30347b546p0, 0x1.8350cd30ac390p0,
+    0x1.865a7772164c5p0, 0x1.896a3b1f66a0ep0, 0x1.8c802477b0010p0,
+    0x1.8f9c3fd29beafp0, 0x1.92be99a09bf00p0, 0x1.95e73e6b1b75ep0,
+    0x1.99163ad4b1dccp0, 0x1.9c4b9b995509bp0, 0x1.9f876d8e8c566p0,
+    0x1.a2c9bda3a3e78p0, 0x1.a61298e1e069cp0, 0x1.a9620c6cb3374p0,
+    0x1.acb82581eee54p0, 0x1.b014f179fc3b8p0, 0x1.b3787dc80f95fp0,
+    0x1.b6e2d7fa5eb18p0, 0x1.ba540dba56e56p0, 0x1.bdcc2cccd3c85p0,
+    0x1.c14b431256446p0, 0x1.c4d15e873c193p0, 0x1.c85e8d43f7cd0p0,
+    0x1.cbf2dd7d490f2p0, 0x1.cf8e5d84758a9p0, 0x1.d3311bc7822b4p0,
+    0x1.d6db26d16cd67p0, 0x1.da8c8d4a66969p0, 0x1.de455df80e3c0p0,
+    0x1.e205a7bdab73ep0, 0x1.e5cd799c6a54ep0, 0x1.e99ce2b397649p0,
+    0x1.ed73f240dc142p0, 0x1.f152b7a07bb76p0, 0x1.f539424d90f5ep0,
+    0x1.f927a1e24bb76p0, 0x1.fd1de6182f8c9p0, 0x1.008e0f64294abp1,
+    0x1.02912df5ce72ap1, 0x1.049856cd84339p1, 0x1.06a39207f0a09p1,
+    0x1.08b2e7d2035cfp1, 0x1.0ac6606916501p1, 0x1.0cde041b0e9aep1,
+    0x1.0ef9db467dcf8p1, 0x1.1119ee5ac36b6p1, 0x1.133e45d82e952p1,
+    0x1.1566ea50201d7p1, 0x1.1793e4652cc50p1, 0x1.19c53ccb3fc6bp1,
+    0x1.1bfafc47bda73p1, 0x1.1e352bb1a74adp1, 0x1.2073d3f1bd518p1,
+    0x1.22b6fe02a3b9cp1, 0x1.24feb2f105cb8p1, 0x1.274afbdbba4a6p1,
+    0x1.299be1f3e7f1cp1, 0x1.2bf16e7d2a38cp1, 0x1.2e4baacdb6614p1,
+    0x1.30aaa04e80d05p1, 0x1.330e587b62b28p1, 0x1.3576dce33feadp1,
+    0x1.37e437282d4eep1, 0x1.3a5670ff972edp1, 0x1.3ccd9432682b4p1,
+    0x1.3f49aa9d30590p1, 0x1.41cabe304cb34p1, 0x1.4450d8f00edd4p1,
+    0x1.46dc04f4e5338p1, 0x1.496c4c6b832dap1, 0x1.4c01b9950a111p1,
+    0x1.4e9c56c731f5dp1, 0x1.513c2e6c731d7p1, 0x1.53e14b042f9cap1,
+    0x1.568bb722dd593p1, 0x1.593b7d72305bbp1,
+};
+
+} // namespace math
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_MATH_EXP_FLOAT_CONSTANTS_H
diff --git a/libc/src/__support/math/expf.h b/libc/src/__support/math/expf.h
new file mode 100644
index 0000000000000..88c151492a041
--- /dev/null
+++ b/libc/src/__support/math/expf.h
@@ -0,0 +1,116 @@
+//===-- Implementation header for expf --------------------------*- 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_EXPF_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_EXPF_H
+
+#include "exp_float_constants.h" // Lookup tables EXP_M1 and EXP_M2.
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/PolyEval.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" // LIBC_UNLIKELY
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+static constexpr float expf(float x) {
+  using FPBits = typename fputil::FPBits<float>;
+  FPBits xbits(x);
+
+  uint32_t x_u = xbits.uintval();
+  uint32_t x_abs = x_u & 0x7fff'ffffU;
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+  // Exceptional values
+  if (LIBC_UNLIKELY(x_u == 0xc236'bd8cU)) { // x = -0x1.6d7b18p+5f
+    return 0x1.108a58p-66f - x * 0x1.0p-95f;
+  }
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+  // When |x| >= 89, |x| < 2^-25, or x is nan
+  if (LIBC_UNLIKELY(x_abs >= 0x42b2'0000U || x_abs <= 0x3280'0000U)) {
+    // |x| < 2^-25
+    if (xbits.get_biased_exponent() <= 101) {
+      return 1.0f + x;
+    }
+
+    // When x < log(2^-150) or nan
+    if (xbits.uintval() >= 0xc2cf'f1b5U) {
+      // exp(-Inf) = 0
+      if (xbits.is_inf())
+        return 0.0f;
+      // exp(nan) = nan
+      if (xbits.is_nan())
+        return x;
+      if (fputil::fenv_is_round_up())
+        return FPBits::min_subnormal().get_val();
+      fputil::set_errno_if_required(ERANGE);
+      fputil::raise_except_if_required(FE_UNDERFLOW);
+      return 0.0f;
+    }
+    // x >= 89 or nan
+    if (xbits.is_pos() && (xbits.uintval() >= 0x42b2'0000)) {
+      // x is finite
+      if (xbits.uintval() < 0x7f80'0000U) {
+        int rounding = fputil::quick_get_round();
+        if (rounding == FE_DOWNWARD || rounding == FE_TOWARDZERO)
+          return FPBits::max_normal().get_val();
+
+        fputil::set_errno_if_required(ERANGE);
+        fputil::raise_except_if_required(FE_OVERFLOW);
+      }
+      // x is +inf or nan
+      return x + FPBits::inf().get_val();
+    }
+  }
+  // For -104 < x < 89, to compute exp(x), we perform the following range
+  // reduction: find hi, mid, lo such that:
+  //   x = hi + mid + lo, in which
+  //     hi is an integer,
+  //     mid * 2^7 is an integer
+  //     -2^(-8) <= lo < 2^-8.
+  // In particular,
+  //   hi + mid = round(x * 2^7) * 2^(-7).
+  // Then,
+  //   exp(x) = exp(hi + mid + lo) = exp(hi) * exp(mid) * exp(lo).
+  // We store exp(hi) and exp(mid) in the lookup tables EXP_M1 and EXP_M2
+  // respectively.  exp(lo) is computed using a degree-4 minimax polynomial
+  // generated by Sollya.
+
+  // x_hi = (hi + mid) * 2^7 = round(x * 2^7).
+  float kf = fputil::nearest_integer(x * 0x1.0p7f);
+  // Subtract (hi + mid) from x to get lo.
+  double xd = static_cast<double>(fputil::multiply_add(kf, -0x1.0p-7f, x));
+  int x_hi = static_cast<int>(kf);
+  x_hi += 104 << 7;
+  // hi = x_hi >> 7
+  double exp_hi = EXP_M1[x_hi >> 7];
+  // mid * 2^7 = x_hi & 0x0000'007fU;
+  double exp_mid = EXP_M2[x_hi & 0x7f];
+  // Degree-4 minimax polynomial generated by Sollya with the following
+  // commands:
+  //   > display = hexadecimal;
+  //   > Q = fpminimax(expm1(x)/x, 3, [|D...|], [-2^-8, 2^-8]);
+  //   > Q;
+  double exp_lo =
+      fputil::polyeval(xd, 0x1p0, 0x1.ffffffffff777p-1, 0x1.000000000071cp-1,
+                       0x1.555566668e5e7p-3, 0x1.55555555ef243p-5);
+  return static_cast<float>(exp_hi * exp_mid * exp_lo);
+}
+
+} // namespace math
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_MATH_EXPF_H
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index db3ef8886b52b..fd1e6c0d648aa 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -1321,15 +1321,7 @@ add_entrypoint_object(
   HDRS
     ../expf.h
   DEPENDS
-    .common_constants
-    libc.src.__support.FPUtil.basic_operations
-    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
     libc.src.errno.errno
 )
 
diff --git a/libc/src/math/generic/expf.cpp b/libc/src/math/generic/expf.cpp
index fa507d4d9322c..de11f51ac64a0 100644
--- a/libc/src/math/generic/expf.cpp
+++ b/libc/src/math/generic/expf.cpp
@@ -7,103 +7,10 @@
 //===----------------------------------------------------------------------===//
 
 #include "src/math/expf.h"
-#include "common_constants.h" // Lookup tables EXP_M1 and EXP_M2.
-#include "src/__support/FPUtil/BasicOperations.h"
-#include "src/__support/FPUtil/FEnvImpl.h"
-#include "src/__support/FPUtil/FPBits.h"
-#include "src/__support/FPUtil/PolyEval.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" // LIBC_UNLIKELY
+#include "src/__support/math/expf.h"
 
 namespace LIBC_NAMESPACE_DECL {
 
-LLVM_LIBC_FUNCTION(float, expf, (float x)) {
-  using FPBits = typename fputil::FPBits<float>;
-  FPBits xbits(x);
-
-  uint32_t x_u = xbits.uintval();
-  uint32_t x_abs = x_u & 0x7fff'ffffU;
-
-#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-  // Exceptional values
-  if (LIBC_UNLIKELY(x_u == 0xc236'bd8cU)) { // x = -0x1.6d7b18p+5f
-    return 0x1.108a58p-66f - x * 0x1.0p-95f;
-  }
-#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-
-  // When |x| >= 89, |x| < 2^-25, or x is nan
-  if (LIBC_UNLIKELY(x_abs >= 0x42b2'0000U || x_abs <= 0x3280'0000U)) {
-    // |x| < 2^-25
-    if (xbits.get_biased_exponent() <= 101) {
-      return 1.0f + x;
-    }
-
-    // When x < log(2^-150) or nan
-    if (xbits.uintval() >= 0xc2cf'f1b5U) {
-      // exp(-Inf) = 0
-      if (xbits.is_inf())
-        return 0.0f;
-      // exp(nan) = nan
-      if (xbits.is_nan())
-        return x;
-      if (fputil::fenv_is_round_up())
-        return FPBits::min_subnormal().get_val();
-      fputil::set_errno_if_required(ERANGE);
-      fputil::raise_except_if_required(FE_UNDERFLOW);
-      return 0.0f;
-    }
-    // x >= 89 or nan
-    if (xbits.is_pos() && (xbits.uintval() >= 0x42b2'0000)) {
-      // x is finite
-      if (xbits.uintval() < 0x7f80'0000U) {
-        int rounding = fputil::quick_get_round();
-        if (rounding == FE_DOWNWARD || rounding == FE_TOWARDZERO)
-          return FPBits::max_normal().get_val();
-
-        fputil::set_errno_if_required(ERANGE);
-        fputil::raise_except_if_required(FE_OVERFLOW);
-      }
-      // x is +inf or nan
-      return x + FPBits::inf().get_val();
-    }
-  }
-  // For -104 < x < 89, to compute exp(x), we perform the following range
-  // reduction: find hi, mid, lo such that:
-  //   x = hi + mid + lo, in which
-  //     hi is an integer,
-  //     mid * 2^7 is an integer
-  //     -2^(-8) <= lo < 2^-8.
-  // In particular,
-  //   hi + mid = round(x * 2^7) * 2^(-7).
-  // Then,
-  //   exp(x) = exp(hi + mid + lo) = exp(hi) * exp(mid) * exp(lo).
-  // We store exp(hi) and exp(mid) in the lookup tables EXP_M1 and EXP_M2
-  // respectively.  exp(lo) is computed using a degree-4 minimax polynomial
-  // generated by Sollya.
-
-  // x_hi = (hi + mid) * 2^7 = round(x * 2^7).
-  float kf = fputil::nearest_integer(x * 0x1.0p7f);
-  // Subtract (hi + mid) from x to get lo.
-  double xd = static_cast<double>(fputil::multiply_add(kf, -0x1.0p-7f, x));
-  int x_hi = static_cast<int>(kf);
-  x_hi += 104 << 7;
-  // hi = x_hi >> 7
-  double exp_hi = EXP_M1[x_hi >> 7];
-  // mid * 2^7 = x_hi & 0x0000'007fU;
-  double exp_mid = EXP_M2[x_hi & 0x7f];
-  // Degree-4 minimax polynomial generated by Sollya with the following
-  // commands:
-  //   > display = hexadecimal;
-  //   > Q = fpminimax(expm1(x)/x, 3, [|D...|], [-2^-8, 2^-8]);
-  //   > Q;
-  double exp_lo =
-      fputil::polyeval(xd, 0x1p0, 0x1.ffffffffff777p-1, 0x1.000000000071cp-1,
-                       0x1.555566668e5e7p-3, 0x1.55555555ef243p-5);
-  return static_cast<float>(exp_hi * exp_mid * exp_lo);
-}
+LLVM_LIBC_FUNCTION(float, expf, (float...
[truncated]

michaelrj-google

LGTM

libc/shared/math.h

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

utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl

…port/math folder. (llvm#143790) This is a step 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

[libc][math] Refactor expf implementation to header-only in src/__sup…

dea47fd

…port/math folder.

lntue requested review from vonosmas, overmighty, jhuber6 and michaelrj-google June 11, 2025 21:39

lntue requested review from rupprecht, keith and aaronmondal as code owners June 11, 2025 21:39

llvmbot added libc bazel "Peripheral" support tier build system: utils/bazel labels Jun 11, 2025

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Add function-specific shared header and add support bazel targets.

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lntue merged commit d1ca8d8 into llvm:main Jun 12, 2025
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