[libc][math] Refactor exp2m1f implementation to header-only in src/__support/math folder. #162017

bassiounix · 2025-10-05T14:34:14Z

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

bassiounix · 2025-10-05T14:35:30Z

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[libc][math] Refactor expm1f16 implementation to header-only in src/__support/math folder. #162132
[libc][math] Refactor expm1f implementation to header-only in src/__support/math folder. #162131
[libc][math] Refactor expm1 implementation to header-only in src/__support/math folder. #162127
[libc][math] Refactor exp2m1f16 implementation to header-only in src/__support/math folder. #162019
[libc][math] Refactor exp2m1f implementation to header-only in src/__support/math folder. #162017 👈 (View in Graphite)
[libc][math] Refactor exp2f16 implementation to header-only in src/__support/math folder. #161993
[libc][math] Refactor exp2f implementation to header-only in src/__support/math folder. #161992
[libc][math] Refactor exp2 implementation to header-only in src/__support/math folder. #161297
[libc][math] Refactor exp10m1f16 implementation to header-only in src/__support/math folder. #161119
[libc][math] Refactor exp10m1f implementation to header-only in src/__support/math folder. #159897
[libc][math] Refactor dsqrtl implementation to header-only in src/__support/math folder. #154868
[libc][math] Refactor cospif16 implementation to header-only in src/__support/math folder. #154222
[libc][math] Refactor cospif implementation to header-only in src/__support/math folder. #154215
[libc][math] Refactor coshf16 implementation to header-only in src/__support/math folder. #153582
[libc][math] Refactor coshf implementation to header-only in src/__support/math folder. #153427
[libc][math] Refactor cosf16 implementation to header-only in src/__support/math folder. #152871
[libc][math] Refactor cosf implementation to header-only in src/__support/math folder. #152069
[libc][math] Refactor cos implementation to header-only in src/__support/math folder. #151883
[libc][math] Refactor cbrtf implementation to header-only in src/__support/math folder. #151846
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[libc][math] Refactor atanhf16 implementation to header-only in src/__support/math folder. #151779
[libc][math] Refactor atanhf implementation to header-only in src/__support/math folder. #151399
[libc][math] Refactor atan2f128 implementation to header-only in src/__support/math folder. #151012
[libc][math] Refactor atan2f implementation to header-only in src/__support/math folder. #150993
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[libc][math] Refactor atanf16 implementation to header-only in src/__support/math folder. #150868
[libc][math] Refactor atanf implementation to header-only in src/__support/math folder. #150854
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[libc][math] Refactor asinhf implementation to header-only in src/__support/math folder. #150843
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llvmbot · 2025-10-05T14:36:14Z

@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

Patch is 20.48 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/162017.diff

9 Files Affected:

(modified) libc/shared/math.h (+1)
(added) libc/shared/math/exp2m1f.h (+23)
(modified) libc/src/__support/math/CMakeLists.txt (+18)
(added) libc/src/__support/math/exp2m1f.h (+196)
(modified) libc/src/math/generic/CMakeLists.txt (+1-11)
(modified) libc/src/math/generic/exp2m1f.cpp (+2-175)
(modified) libc/test/shared/CMakeLists.txt (+1)
(modified) libc/test/shared/shared_math_test.cpp (+1)
(modified) utils/bazel/llvm-project-overlay/libc/BUILD.bazel (+17-2)

diff --git a/libc/shared/math.h b/libc/shared/math.h
index 8bff70f1c5336..0c0e8560bd40f 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 185900efa7354..ec2d8948f615b 100644
--- a/libc/src/__support/math/CMakeLists.txt
+++ b/libc/src/__support/math/CMakeLists.txt
@@ -767,6 +767,24 @@ 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..b68304cb1403d
--- /dev/null
+++ b/libc/src/__support/math/exp2m1f.h
@@ -0,0 +1,196 @@
+//===-- 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 8e969de5a8031..5fc741b36d844 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -1478,17 +1478,7 @@ 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 685b954c1f306..9970fce1c1a19 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 b114eefccbf77..cd9002b5a2e52 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 d47e5feb7eff8..f79a3944b13d3 100644
--- a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
@@ -2911,6 +2911,22 @@ 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...
[truncated]

…support/math folder.

bassiounix requested a review from lntue October 5, 2025 14:35

bassiounix added bazel "Peripheral" support tier build system: utils/bazel libc labels Oct 5, 2025 — with Graphite App

bassiounix marked this pull request as ready for review October 5, 2025 14:36

bassiounix requested review from rupprecht, keith and aaronmondal as code owners October 5, 2025 14:36

bassiounix removed the request for review from aaronmondal October 5, 2025 14:36

bassiounix removed request for keith and rupprecht October 5, 2025 14:36

bassiounix mentioned this pull request Oct 5, 2025

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

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bassiounix force-pushed the users/bassiounix/spr/10-05-_libc_math_refactor_exp2m1f_implementation_to_header-only_in_src___support_math_folder branch 2 times, most recently from 33f208d to f2e2010 Compare October 5, 2025 14:54

bassiounix mentioned this pull request Oct 5, 2025

[libc][math] Refactor exp2m1f16 implementation to header-only in src/__support/math folder. #162019

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bassiounix force-pushed the users/bassiounix/spr/10-05-_libc_math_refactor_exp2f16_implementation_to_header-only_in_src___support_math_folder branch from 8bf9344 to ce1bed7 Compare October 6, 2025 17:42

bassiounix force-pushed the users/bassiounix/spr/10-05-_libc_math_refactor_exp2m1f_implementation_to_header-only_in_src___support_math_folder branch from f2e2010 to c771895 Compare October 6, 2025 17:42

bassiounix mentioned this pull request Oct 6, 2025

[libc][math] Refactor expm1 implementation to header-only in src/__support/math folder. #162127

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bassiounix force-pushed the users/bassiounix/spr/10-05-_libc_math_refactor_exp2f16_implementation_to_header-only_in_src___support_math_folder branch from ce1bed7 to 7f96a60 Compare October 6, 2025 18:03

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bassiounix mentioned this pull request Oct 6, 2025

[libc][math] Refactor expm1f implementation to header-only in src/__support/math folder. #162131

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bassiounix force-pushed the users/bassiounix/spr/10-05-_libc_math_refactor_exp2f16_implementation_to_header-only_in_src___support_math_folder branch from 7f96a60 to f948445 Compare October 6, 2025 18:25

[libc][math] Refactor exp2m1f implementation to header-only in src/__…

3c21f84

…support/math folder.

bassiounix force-pushed the users/bassiounix/spr/10-05-_libc_math_refactor_exp2f16_implementation_to_header-only_in_src___support_math_folder branch from f948445 to d4c0678 Compare October 6, 2025 18:28

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bassiounix mentioned this pull request Oct 6, 2025

[libc][math] Refactor expm1f16 implementation to header-only in src/__support/math folder. #162132

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