[libc] [llvm] [libc][math] Refactor exp2m1f implementation to header-only in src/__support/math folder. (PR #162017)
Muhammad Bassiouni via llvm-commits
llvm-commits at lists.llvm.org
Sat Oct 11 13:29:07 PDT 2025
https://github.com/bassiounix updated https://github.com/llvm/llvm-project/pull/162017
>From 899dfd362ff33beb5697702adac89e8175d65ef7 Mon Sep 17 00:00:00 2001
From: bassiounix <muhammad.m.bassiouni at gmail.com>
Date: Sun, 5 Oct 2025 17:52:54 +0300
Subject: [PATCH] [libc][math] Refactor exp2m1f implementation to header-only
in src/__support/math folder.
---
libc/shared/math.h | 1 +
libc/shared/math/exp2m1f.h | 23 +++
libc/src/__support/math/CMakeLists.txt | 18 ++
libc/src/__support/math/exp2m1f.h | 195 ++++++++++++++++++
libc/src/math/generic/CMakeLists.txt | 12 +-
libc/src/math/generic/exp2m1f.cpp | 177 +---------------
libc/test/shared/CMakeLists.txt | 1 +
libc/test/shared/shared_math_test.cpp | 1 +
.../llvm-project-overlay/libc/BUILD.bazel | 19 +-
9 files changed, 259 insertions(+), 188 deletions(-)
create mode 100644 libc/shared/math/exp2m1f.h
create mode 100644 libc/src/__support/math/exp2m1f.h
diff --git a/libc/shared/math.h b/libc/shared/math.h
index e3f7965e19a55..bd6aee73c3933 100644
--- a/libc/shared/math.h
+++ b/libc/shared/math.h
@@ -50,6 +50,7 @@
#include "math/exp2.h"
#include "math/exp2f.h"
#include "math/exp2f16.h"
+#include "math/exp2m1f.h"
#include "math/expf.h"
#include "math/expf16.h"
#include "math/frexpf.h"
diff --git a/libc/shared/math/exp2m1f.h b/libc/shared/math/exp2m1f.h
new file mode 100644
index 0000000000000..ca9754774f0fc
--- /dev/null
+++ b/libc/shared/math/exp2m1f.h
@@ -0,0 +1,23 @@
+//===-- Shared exp2m1f 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_EXP2M1F_H
+#define LLVM_LIBC_SHARED_MATH_EXP2M1F_H
+
+#include "shared/libc_common.h"
+#include "src/__support/math/exp2m1f.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace shared {
+
+using math::exp2m1f;
+
+} // namespace shared
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SHARED_MATH_EXP2M1F_H
diff --git a/libc/src/__support/math/CMakeLists.txt b/libc/src/__support/math/CMakeLists.txt
index 9685496c0ec41..47bb3282cce21 100644
--- a/libc/src/__support/math/CMakeLists.txt
+++ b/libc/src/__support/math/CMakeLists.txt
@@ -751,6 +751,24 @@ add_header_library(
libc.src.__support.macros.optimization
)
+add_header_library(
+ exp2m1f
+ HDRS
+ exp2m1f.h
+ DEPENDS
+ .exp10f_utils
+ libc.src.errno.errno
+ libc.src.__support.common
+ 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.polyeval
+ libc.src.__support.FPUtil.rounding_mode
+ libc.src.__support.macros.optimization
+ libc.src.__support.macros.properties.cpu_features
+)
+
add_header_library(
exp10
HDRS
diff --git a/libc/src/__support/math/exp2m1f.h b/libc/src/__support/math/exp2m1f.h
new file mode 100644
index 0000000000000..e95076c9eac22
--- /dev/null
+++ b/libc/src/__support/math/exp2m1f.h
@@ -0,0 +1,195 @@
+//===-- Implementation header for exp2m1f ------------------------*- 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_EXP2M1F_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_EXP2M1F_H
+
+#include "exp10f_utils.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/PolyEval.h"
+#include "src/__support/FPUtil/except_value_utils.h"
+#include "src/__support/FPUtil/multiply_add.h"
+#include "src/__support/FPUtil/rounding_mode.h"
+#include "src/__support/common.h"
+#include "src/__support/libc_errno.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h"
+#include "src/__support/macros/properties/cpu_features.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+LIBC_INLINE static constexpr float exp2m1f(float x) {
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+ constexpr size_t N_EXCEPTS_LO = 8;
+
+ constexpr fputil::ExceptValues<float, N_EXCEPTS_LO> EXP2M1F_EXCEPTS_LO = {{
+ // (input, RZ output, RU offset, RD offset, RN offset)
+ // x = 0x1.36dc8ep-36, exp2m1f(x) = 0x1.aef212p-37 (RZ)
+ {0x2d9b'6e47U, 0x2d57'7909U, 1U, 0U, 0U},
+ // x = 0x1.224936p-19, exp2m1f(x) = 0x1.926c0ep-20 (RZ)
+ {0x3611'249bU, 0x35c9'3607U, 1U, 0U, 1U},
+ // x = 0x1.d16d2p-20, exp2m1f(x) = 0x1.429becp-20 (RZ)
+ {0x35e8'b690U, 0x35a1'4df6U, 1U, 0U, 1U},
+ // x = 0x1.17949ep-14, exp2m1f(x) = 0x1.8397p-15 (RZ)
+ {0x388b'ca4fU, 0x3841'cb80U, 1U, 0U, 1U},
+ // x = -0x1.9c3e1ep-38, exp2m1f(x) = -0x1.1dbeacp-38 (RZ)
+ {0xacce'1f0fU, 0xac8e'df56U, 0U, 1U, 0U},
+ // x = -0x1.4d89b4p-32, exp2m1f(x) = -0x1.ce61b6p-33 (RZ)
+ {0xafa6'c4daU, 0xaf67'30dbU, 0U, 1U, 1U},
+ // x = -0x1.a6eac4p-10, exp2m1f(x) = -0x1.24fadap-10 (RZ)
+ {0xbad3'7562U, 0xba92'7d6dU, 0U, 1U, 1U},
+ // x = -0x1.e7526ep-6, exp2m1f(x) = -0x1.4e53dep-6 (RZ)
+ {0xbcf3'a937U, 0xbca7'29efU, 0U, 1U, 1U},
+ }};
+
+ constexpr size_t N_EXCEPTS_HI = 3;
+
+ constexpr fputil::ExceptValues<float, N_EXCEPTS_HI> EXP2M1F_EXCEPTS_HI = {{
+ // (input, RZ output, RU offset, RD offset, RN offset)
+ // x = 0x1.16a972p-1, exp2m1f(x) = 0x1.d545b2p-2 (RZ)
+ {0x3f0b'54b9U, 0x3eea'a2d9U, 1U, 0U, 0U},
+ // x = -0x1.9f12acp-5, exp2m1f(x) = -0x1.1ab68cp-5 (RZ)
+ {0xbd4f'8956U, 0xbd0d'5b46U, 0U, 1U, 0U},
+ // x = -0x1.de7b9cp-5, exp2m1f(x) = -0x1.4508f4p-5 (RZ)
+ {0xbd6f'3dceU, 0xbd22'847aU, 0U, 1U, 1U},
+ }};
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+ using FPBits = fputil::FPBits<float>;
+ FPBits xbits(x);
+
+ uint32_t x_u = xbits.uintval();
+ uint32_t x_abs = x_u & 0x7fff'ffffU;
+
+ // When |x| >= 128, or x is nan, or |x| <= 2^-5
+ if (LIBC_UNLIKELY(x_abs >= 0x4300'0000U || x_abs <= 0x3d00'0000U)) {
+ // |x| <= 2^-5
+ if (x_abs <= 0x3d00'0000U) {
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+ if (auto r = EXP2M1F_EXCEPTS_LO.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
+ return r.value();
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+ // Minimax polynomial generated by Sollya with:
+ // > display = hexadecimal;
+ // > fpminimax((2^x - 1)/x, 5, [|D...|], [-2^-5, 2^-5]);
+ constexpr double COEFFS[] = {
+ 0x1.62e42fefa39f3p-1, 0x1.ebfbdff82c57bp-3, 0x1.c6b08d6f2d7aap-5,
+ 0x1.3b2ab6fc92f5dp-7, 0x1.5d897cfe27125p-10, 0x1.43090e61e6af1p-13};
+ double xd = x;
+ double xsq = xd * xd;
+ double c0 = fputil::multiply_add(xd, COEFFS[1], COEFFS[0]);
+ double c1 = fputil::multiply_add(xd, COEFFS[3], COEFFS[2]);
+ double c2 = fputil::multiply_add(xd, COEFFS[5], COEFFS[4]);
+ double p = fputil::polyeval(xsq, c0, c1, c2);
+ return static_cast<float>(p * xd);
+ }
+
+ // x >= 128, or x is nan
+ if (xbits.is_pos()) {
+ if (xbits.is_finite()) {
+ 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 >= 128 and 2^x - 1 rounds to +inf, or x is +inf or nan
+ return x + FPBits::inf().get_val();
+ }
+ }
+
+ if (LIBC_UNLIKELY(x <= -25.0f)) {
+ // 2^(-inf) - 1 = -1
+ if (xbits.is_inf())
+ return -1.0f;
+ // 2^nan - 1 = nan
+ if (xbits.is_nan())
+ return x;
+
+ int rounding = fputil::quick_get_round();
+ if (rounding == FE_UPWARD || rounding == FE_TOWARDZERO)
+ return -0x1.ffff'fep-1f; // -1.0f + 0x1.0p-24f
+
+ fputil::set_errno_if_required(ERANGE);
+ fputil::raise_except_if_required(FE_UNDERFLOW);
+ return -1.0f;
+ }
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+ if (auto r = EXP2M1F_EXCEPTS_HI.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
+ return r.value();
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+ // For -25 < x < 128, to compute 2^x, we perform the following range
+ // reduction: find hi, mid, lo such that:
+ // x = hi + mid + lo, in which:
+ // hi is an integer,
+ // 0 <= mid * 2^5 < 32 is an integer,
+ // -2^(-6) <= lo <= 2^(-6).
+ // In particular,
+ // hi + mid = round(x * 2^5) * 2^(-5).
+ // Then,
+ // 2^x = 2^(hi + mid + lo) = 2^hi * 2^mid * 2^lo.
+ // 2^mid is stored in the lookup table of 32 elements.
+ // 2^lo is computed using a degree-4 minimax polynomial generated by Sollya.
+ // We perform 2^hi * 2^mid by simply add hi to the exponent field of 2^mid.
+
+ // kf = (hi + mid) * 2^5 = round(x * 2^5)
+ float kf = 0;
+ int k = 0;
+#ifdef LIBC_TARGET_CPU_HAS_NEAREST_INT
+ kf = fputil::nearest_integer(x * 32.0f);
+ k = static_cast<int>(kf);
+#else
+ constexpr float HALF[2] = {0.5f, -0.5f};
+ k = static_cast<int>(fputil::multiply_add(x, 32.0f, HALF[x < 0.0f]));
+ kf = static_cast<float>(k);
+#endif // LIBC_TARGET_CPU_HAS_NEAREST_INT
+
+ // lo = x - (hi + mid) = x - kf * 2^(-5)
+ double lo = fputil::multiply_add(-0x1.0p-5f, kf, x);
+
+ // hi = floor(kf * 2^(-4))
+ // exp2_hi = shift hi to the exponent field of double precision.
+ int64_t exp2_hi =
+ static_cast<int64_t>(static_cast<uint64_t>(k >> ExpBase::MID_BITS)
+ << fputil::FPBits<double>::FRACTION_LEN);
+ // mh = 2^hi * 2^mid
+ // mh_bits = bit field of mh
+ int64_t mh_bits = ExpBase::EXP_2_MID[k & ExpBase::MID_MASK] + exp2_hi;
+ double mh = fputil::FPBits<double>(static_cast<uint64_t>(mh_bits)).get_val();
+
+ // Degree-4 polynomial approximating (2^x - 1)/x generated by Sollya with:
+ // > display = hexadecimal;
+ // > fpminimax((2^x - 1)/x, 4, [|D...|], [-2^-6, 2^-6]);
+ constexpr double COEFFS[5] = {0x1.62e42fefa39efp-1, 0x1.ebfbdff8131c4p-3,
+ 0x1.c6b08d7061695p-5, 0x1.3b2b1bee74b2ap-7,
+ 0x1.5d88091198529p-10};
+ double lo_sq = lo * lo;
+ double c1 = fputil::multiply_add(lo, COEFFS[0], 1.0);
+ double c2 = fputil::multiply_add(lo, COEFFS[2], COEFFS[1]);
+ double c3 = fputil::multiply_add(lo, COEFFS[4], COEFFS[3]);
+ double exp2_lo = fputil::polyeval(lo_sq, c1, c2, c3);
+ // 2^x - 1 = 2^(hi + mid + lo) - 1
+ // = 2^(hi + mid) * 2^lo - 1
+ // ~ mh * (1 + lo * P(lo)) - 1
+ // = mh * exp2_lo - 1
+ return static_cast<float>(fputil::multiply_add(exp2_lo, mh, -1.0));
+}
+
+} // namespace math
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC___SUPPORT_MATH_EXP2M1F_H
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index 0754b5e0b08e1..6068c36e558ef 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -1488,17 +1488,7 @@ add_entrypoint_object(
HDRS
../exp2m1f.h
DEPENDS
- libc.src.errno.errno
- libc.src.__support.common
- 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.polyeval
- libc.src.__support.FPUtil.rounding_mode
- libc.src.__support.macros.optimization
- libc.src.__support.macros.properties.cpu_features
- libc.src.__support.math.exp10f_utils
+ libc.src.__support.math.exp2m1f
)
add_entrypoint_object(
diff --git a/libc/src/math/generic/exp2m1f.cpp b/libc/src/math/generic/exp2m1f.cpp
index 16244edb4c583..14d026f1cb84e 100644
--- a/libc/src/math/generic/exp2m1f.cpp
+++ b/libc/src/math/generic/exp2m1f.cpp
@@ -7,183 +7,10 @@
//===----------------------------------------------------------------------===//
#include "src/math/exp2m1f.h"
-#include "src/__support/FPUtil/FEnvImpl.h"
-#include "src/__support/FPUtil/FPBits.h"
-#include "src/__support/FPUtil/PolyEval.h"
-#include "src/__support/FPUtil/except_value_utils.h"
-#include "src/__support/FPUtil/multiply_add.h"
-#include "src/__support/FPUtil/rounding_mode.h"
-#include "src/__support/common.h"
-#include "src/__support/libc_errno.h"
-#include "src/__support/macros/config.h"
-#include "src/__support/macros/optimization.h"
-#include "src/__support/macros/properties/cpu_features.h"
-#include "src/__support/math/exp10f_utils.h"
+#include "src/__support/math/exp2m1f.h"
namespace LIBC_NAMESPACE_DECL {
-#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-static constexpr size_t N_EXCEPTS_LO = 8;
-
-static constexpr fputil::ExceptValues<float, N_EXCEPTS_LO> EXP2M1F_EXCEPTS_LO =
- {{
- // (input, RZ output, RU offset, RD offset, RN offset)
- // x = 0x1.36dc8ep-36, exp2m1f(x) = 0x1.aef212p-37 (RZ)
- {0x2d9b'6e47U, 0x2d57'7909U, 1U, 0U, 0U},
- // x = 0x1.224936p-19, exp2m1f(x) = 0x1.926c0ep-20 (RZ)
- {0x3611'249bU, 0x35c9'3607U, 1U, 0U, 1U},
- // x = 0x1.d16d2p-20, exp2m1f(x) = 0x1.429becp-20 (RZ)
- {0x35e8'b690U, 0x35a1'4df6U, 1U, 0U, 1U},
- // x = 0x1.17949ep-14, exp2m1f(x) = 0x1.8397p-15 (RZ)
- {0x388b'ca4fU, 0x3841'cb80U, 1U, 0U, 1U},
- // x = -0x1.9c3e1ep-38, exp2m1f(x) = -0x1.1dbeacp-38 (RZ)
- {0xacce'1f0fU, 0xac8e'df56U, 0U, 1U, 0U},
- // x = -0x1.4d89b4p-32, exp2m1f(x) = -0x1.ce61b6p-33 (RZ)
- {0xafa6'c4daU, 0xaf67'30dbU, 0U, 1U, 1U},
- // x = -0x1.a6eac4p-10, exp2m1f(x) = -0x1.24fadap-10 (RZ)
- {0xbad3'7562U, 0xba92'7d6dU, 0U, 1U, 1U},
- // x = -0x1.e7526ep-6, exp2m1f(x) = -0x1.4e53dep-6 (RZ)
- {0xbcf3'a937U, 0xbca7'29efU, 0U, 1U, 1U},
- }};
-
-static constexpr size_t N_EXCEPTS_HI = 3;
-
-static constexpr fputil::ExceptValues<float, N_EXCEPTS_HI> EXP2M1F_EXCEPTS_HI =
- {{
- // (input, RZ output, RU offset, RD offset, RN offset)
- // x = 0x1.16a972p-1, exp2m1f(x) = 0x1.d545b2p-2 (RZ)
- {0x3f0b'54b9U, 0x3eea'a2d9U, 1U, 0U, 0U},
- // x = -0x1.9f12acp-5, exp2m1f(x) = -0x1.1ab68cp-5 (RZ)
- {0xbd4f'8956U, 0xbd0d'5b46U, 0U, 1U, 0U},
- // x = -0x1.de7b9cp-5, exp2m1f(x) = -0x1.4508f4p-5 (RZ)
- {0xbd6f'3dceU, 0xbd22'847aU, 0U, 1U, 1U},
- }};
-#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-
-LLVM_LIBC_FUNCTION(float, exp2m1f, (float x)) {
- using FPBits = fputil::FPBits<float>;
- FPBits xbits(x);
-
- uint32_t x_u = xbits.uintval();
- uint32_t x_abs = x_u & 0x7fff'ffffU;
-
- // When |x| >= 128, or x is nan, or |x| <= 2^-5
- if (LIBC_UNLIKELY(x_abs >= 0x4300'0000U || x_abs <= 0x3d00'0000U)) {
- // |x| <= 2^-5
- if (x_abs <= 0x3d00'0000U) {
-#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
- if (auto r = EXP2M1F_EXCEPTS_LO.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
- return r.value();
-#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-
- // Minimax polynomial generated by Sollya with:
- // > display = hexadecimal;
- // > fpminimax((2^x - 1)/x, 5, [|D...|], [-2^-5, 2^-5]);
- constexpr double COEFFS[] = {
- 0x1.62e42fefa39f3p-1, 0x1.ebfbdff82c57bp-3, 0x1.c6b08d6f2d7aap-5,
- 0x1.3b2ab6fc92f5dp-7, 0x1.5d897cfe27125p-10, 0x1.43090e61e6af1p-13};
- double xd = x;
- double xsq = xd * xd;
- double c0 = fputil::multiply_add(xd, COEFFS[1], COEFFS[0]);
- double c1 = fputil::multiply_add(xd, COEFFS[3], COEFFS[2]);
- double c2 = fputil::multiply_add(xd, COEFFS[5], COEFFS[4]);
- double p = fputil::polyeval(xsq, c0, c1, c2);
- return static_cast<float>(p * xd);
- }
-
- // x >= 128, or x is nan
- if (xbits.is_pos()) {
- if (xbits.is_finite()) {
- 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 >= 128 and 2^x - 1 rounds to +inf, or x is +inf or nan
- return x + FPBits::inf().get_val();
- }
- }
-
- if (LIBC_UNLIKELY(x <= -25.0f)) {
- // 2^(-inf) - 1 = -1
- if (xbits.is_inf())
- return -1.0f;
- // 2^nan - 1 = nan
- if (xbits.is_nan())
- return x;
-
- int rounding = fputil::quick_get_round();
- if (rounding == FE_UPWARD || rounding == FE_TOWARDZERO)
- return -0x1.ffff'fep-1f; // -1.0f + 0x1.0p-24f
-
- fputil::set_errno_if_required(ERANGE);
- fputil::raise_except_if_required(FE_UNDERFLOW);
- return -1.0f;
- }
-
-#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
- if (auto r = EXP2M1F_EXCEPTS_HI.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
- return r.value();
-#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
-
- // For -25 < x < 128, to compute 2^x, we perform the following range
- // reduction: find hi, mid, lo such that:
- // x = hi + mid + lo, in which:
- // hi is an integer,
- // 0 <= mid * 2^5 < 32 is an integer,
- // -2^(-6) <= lo <= 2^(-6).
- // In particular,
- // hi + mid = round(x * 2^5) * 2^(-5).
- // Then,
- // 2^x = 2^(hi + mid + lo) = 2^hi * 2^mid * 2^lo.
- // 2^mid is stored in the lookup table of 32 elements.
- // 2^lo is computed using a degree-4 minimax polynomial generated by Sollya.
- // We perform 2^hi * 2^mid by simply add hi to the exponent field of 2^mid.
-
- // kf = (hi + mid) * 2^5 = round(x * 2^5)
- float kf;
- int k;
-#ifdef LIBC_TARGET_CPU_HAS_NEAREST_INT
- kf = fputil::nearest_integer(x * 32.0f);
- k = static_cast<int>(kf);
-#else
- constexpr float HALF[2] = {0.5f, -0.5f};
- k = static_cast<int>(fputil::multiply_add(x, 32.0f, HALF[x < 0.0f]));
- kf = static_cast<float>(k);
-#endif // LIBC_TARGET_CPU_HAS_NEAREST_INT
-
- // lo = x - (hi + mid) = x - kf * 2^(-5)
- double lo = fputil::multiply_add(-0x1.0p-5f, kf, x);
-
- // hi = floor(kf * 2^(-4))
- // exp2_hi = shift hi to the exponent field of double precision.
- int64_t exp2_hi =
- static_cast<int64_t>(static_cast<uint64_t>(k >> ExpBase::MID_BITS)
- << fputil::FPBits<double>::FRACTION_LEN);
- // mh = 2^hi * 2^mid
- // mh_bits = bit field of mh
- int64_t mh_bits = ExpBase::EXP_2_MID[k & ExpBase::MID_MASK] + exp2_hi;
- double mh = fputil::FPBits<double>(static_cast<uint64_t>(mh_bits)).get_val();
-
- // Degree-4 polynomial approximating (2^x - 1)/x generated by Sollya with:
- // > display = hexadecimal;
- // > fpminimax((2^x - 1)/x, 4, [|D...|], [-2^-6, 2^-6]);
- constexpr double COEFFS[5] = {0x1.62e42fefa39efp-1, 0x1.ebfbdff8131c4p-3,
- 0x1.c6b08d7061695p-5, 0x1.3b2b1bee74b2ap-7,
- 0x1.5d88091198529p-10};
- double lo_sq = lo * lo;
- double c1 = fputil::multiply_add(lo, COEFFS[0], 1.0);
- double c2 = fputil::multiply_add(lo, COEFFS[2], COEFFS[1]);
- double c3 = fputil::multiply_add(lo, COEFFS[4], COEFFS[3]);
- double exp2_lo = fputil::polyeval(lo_sq, c1, c2, c3);
- // 2^x - 1 = 2^(hi + mid + lo) - 1
- // = 2^(hi + mid) * 2^lo - 1
- // ~ mh * (1 + lo * P(lo)) - 1
- // = mh * exp2_lo - 1
- return static_cast<float>(fputil::multiply_add(exp2_lo, mh, -1.0));
-}
+LLVM_LIBC_FUNCTION(float, exp2m1f, (float x)) { return math::exp2m1f(x); }
} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/test/shared/CMakeLists.txt b/libc/test/shared/CMakeLists.txt
index 8d81199f19c83..aede395350821 100644
--- a/libc/test/shared/CMakeLists.txt
+++ b/libc/test/shared/CMakeLists.txt
@@ -43,6 +43,7 @@ add_fp_unittest(
libc.src.__support.math.exp2
libc.src.__support.math.exp2f
libc.src.__support.math.exp2f16
+ libc.src.__support.math.exp2m1f
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 84787d5e02a3a..a6825a10654c9 100644
--- a/libc/test/shared/shared_math_test.cpp
+++ b/libc/test/shared/shared_math_test.cpp
@@ -61,6 +61,7 @@ TEST(LlvmLibcSharedMathTest, AllFloat) {
EXPECT_FP_EQ(0x0p+0f, LIBC_NAMESPACE::shared::exp10m1f(0.0f));
EXPECT_FP_EQ(0x0p+0f, LIBC_NAMESPACE::shared::erff(0.0f));
EXPECT_FP_EQ(0x1p+0f, LIBC_NAMESPACE::shared::exp10f(0.0f));
+ EXPECT_FP_EQ(0x0p+0f, LIBC_NAMESPACE::shared::exp2m1f(0.0f));
EXPECT_FP_EQ(0x1p+0f, LIBC_NAMESPACE::shared::expf(0.0f));
EXPECT_FP_EQ(0x1p+0f, LIBC_NAMESPACE::shared::exp2f(0.0f));
diff --git a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
index 936bc1248b6ef..9413ad09a4979 100644
--- a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
@@ -2932,6 +2932,22 @@ libc_support_library(
],
)
+libc_support_library(
+ name = "__support_math_exp2m1f",
+ hdrs = ["src/__support/math/exp2m1f.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_exp10f_utils",
+ ],
+)
+
libc_support_library(
name = "__support_math_exp10",
hdrs = ["src/__support/math/exp10.h"],
@@ -3719,8 +3735,7 @@ libc_math_function(
libc_math_function(
name = "exp2m1f",
additional_deps = [
- ":__support_fputil_polyeval",
- ":__support_math_exp10f_utils",
+ ":__support_math_exp2m1f",
],
)
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