[libc-commits] [libc] [libc][math][c23] Add exp2m1f C23 math function (PR #86996)

via libc-commits libc-commits at lists.llvm.org
Sun Mar 31 17:40:07 PDT 2024


https://github.com/overmighty updated https://github.com/llvm/llvm-project/pull/86996

>From 601fabe46dd13bb4e2a3b93f723b45632f45c838 Mon Sep 17 00:00:00 2001
From: OverMighty <its.overmighty at gmail.com>
Date: Thu, 28 Mar 2024 19:36:38 +0000
Subject: [PATCH 1/3] [libc][math][c23] Add exp2m1f C23 math function

Fixes #86502.
---
 libc/config/linux/x86_64/entrypoints.txt      |   1 +
 libc/spec/stdc.td                             |   2 +
 libc/src/math/CMakeLists.txt                  |   2 +
 libc/src/math/exp2m1f.h                       |  18 +++
 libc/src/math/generic/CMakeLists.txt          |  21 +++
 libc/src/math/generic/exp2m1f.cpp             | 144 ++++++++++++++++++
 libc/test/src/math/exhaustive/CMakeLists.txt  |  15 ++
 .../test/src/math/exhaustive/exp2m1f_test.cpp |  33 ++++
 libc/test/src/math/smoke/CMakeLists.txt       |  12 ++
 libc/test/src/math/smoke/exp2m1f_test.cpp     |  57 +++++++
 libc/utils/MPFRWrapper/MPFRUtils.cpp          |   8 +
 libc/utils/MPFRWrapper/MPFRUtils.h            |   1 +
 12 files changed, 314 insertions(+)
 create mode 100644 libc/src/math/exp2m1f.h
 create mode 100644 libc/src/math/generic/exp2m1f.cpp
 create mode 100644 libc/test/src/math/exhaustive/exp2m1f_test.cpp
 create mode 100644 libc/test/src/math/smoke/exp2m1f_test.cpp

diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 5b428e51aee620..b1e0592278e18c 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -369,6 +369,7 @@ set(TARGET_LIBM_ENTRYPOINTS
     libc.src.math.exp10f
     libc.src.math.exp2
     libc.src.math.exp2f
+    libc.src.math.exp2m1f
     libc.src.math.expm1
     libc.src.math.expm1f
     libc.src.math.fabs
diff --git a/libc/spec/stdc.td b/libc/spec/stdc.td
index ac6e1d1801ba55..bd72ff9095e2ea 100644
--- a/libc/spec/stdc.td
+++ b/libc/spec/stdc.td
@@ -535,6 +535,8 @@ def StdC : StandardSpec<"stdc"> {
           FunctionSpec<"exp2", RetValSpec<DoubleType>, [ArgSpec<DoubleType>]>,
           FunctionSpec<"exp2f", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
 
+          FunctionSpec<"exp2m1f", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
+
           FunctionSpec<"expm1", RetValSpec<DoubleType>, [ArgSpec<DoubleType>]>,
           FunctionSpec<"expm1f", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
 
diff --git a/libc/src/math/CMakeLists.txt b/libc/src/math/CMakeLists.txt
index b67ee3a8e0dfbd..c89792b8ac7be6 100644
--- a/libc/src/math/CMakeLists.txt
+++ b/libc/src/math/CMakeLists.txt
@@ -88,6 +88,8 @@ add_math_entrypoint_object(expf)
 add_math_entrypoint_object(exp2)
 add_math_entrypoint_object(exp2f)
 
+add_math_entrypoint_object(exp2m1f)
+
 add_math_entrypoint_object(exp10)
 add_math_entrypoint_object(exp10f)
 
diff --git a/libc/src/math/exp2m1f.h b/libc/src/math/exp2m1f.h
new file mode 100644
index 00000000000000..0eaf6b00e958c5
--- /dev/null
+++ b/libc/src/math/exp2m1f.h
@@ -0,0 +1,18 @@
+//===-- 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_MATH_EXP2M1F_H
+#define LLVM_LIBC_SRC_MATH_EXP2M1F_H
+
+namespace LIBC_NAMESPACE {
+
+float exp2m1f(float x);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_MATH_EXP2M1F_H
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index 4d9b91150d0200..c1a4e5ea6e3b9d 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -837,6 +837,27 @@ add_entrypoint_object(
     -O3
 )
 
+add_entrypoint_object(
+  exp2m1f
+  SRCS
+    exp2m1f.cpp
+  HDRS
+    ../exp2m1f.h
+  DEPENDS
+    .explogxf
+    libc.src.errno.errno
+    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.polyeval
+    libc.src.__support.FPUtil.rounding_mode
+    libc.src.__support.macros.optimization
+    libc.src.__support.macros.properties.cpu_features
+  COMPILE_OPTIONS
+    -O3
+)
+
 add_entrypoint_object(
   exp10
   SRCS
diff --git a/libc/src/math/generic/exp2m1f.cpp b/libc/src/math/generic/exp2m1f.cpp
new file mode 100644
index 00000000000000..ea5c637b0b8692
--- /dev/null
+++ b/libc/src/math/generic/exp2m1f.cpp
@@ -0,0 +1,144 @@
+//===-- Implementation of exp2m1f 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
+//
+//===----------------------------------------------------------------------===//
+
+#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/multiply_add.h"
+#include "src/__support/FPUtil/rounding_mode.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/optimization.h"
+#include "src/__support/macros/properties/cpu_features.h"
+#include "src/errno/libc_errno.h"
+
+#include "explogxf.h"
+
+namespace LIBC_NAMESPACE {
+
+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 <= 0x3d00'0000) {
+      // TODO: Handle exceptional values.
+
+      // 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();
+    }
+
+    // x <= -25
+    if (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;
+    }
+  }
+
+  // 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
+
+  // dx = lo = x - (hi + mid) = x - kf * 2^(-5)
+  double dx = fputil::multiply_add(-0x1.0p-5f, kf, x);
+
+  // hi = floor(kf * 2^(-4))
+  // exp_hi = shift hi to the exponent field of double precision.
+  int64_t exp_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] + exp_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 dx_sq = dx * dx;
+  double c1 = fputil::multiply_add(dx, COEFFS[0], 1.0);
+  double c2 = fputil::multiply_add(dx, COEFFS[2], COEFFS[1]);
+  double c3 = fputil::multiply_add(dx, COEFFS[4], COEFFS[3]);
+  double p = fputil::multiply_add(dx_sq, c3, c2);
+  // 2^x = 2^(hi + mid + lo)
+  //     = 2^(hi + mid) * 2^lo
+  //     ~ mh * (1 + lo * P(lo))
+  //     = mh + (mh*lo) * P(lo)
+  double exp2_lo = fputil::multiply_add(p, dx_sq, c1);
+  return static_cast<float>(fputil::multiply_add(exp2_lo, mh, -1.0));
+}
+
+} // namespace LIBC_NAMESPACE
diff --git a/libc/test/src/math/exhaustive/CMakeLists.txt b/libc/test/src/math/exhaustive/CMakeLists.txt
index df32dd4f943f30..6b2f3dddcadd24 100644
--- a/libc/test/src/math/exhaustive/CMakeLists.txt
+++ b/libc/test/src/math/exhaustive/CMakeLists.txt
@@ -142,6 +142,21 @@ add_fp_unittest(
     -lpthread
 )
 
+add_fp_unittest(
+  exp2m1f_test
+  NO_RUN_POSTBUILD
+  NEED_MPFR
+  SUITE
+    libc_math_exhaustive_tests
+  SRCS
+    exp2m1f_test.cpp
+  DEPENDS
+    .exhaustive_test
+    libc.src.math.exp2m1f
+  LINK_LIBRARIES
+    -lpthread
+)
+
 add_fp_unittest(
   exp10f_test
   NO_RUN_POSTBUILD
diff --git a/libc/test/src/math/exhaustive/exp2m1f_test.cpp b/libc/test/src/math/exhaustive/exp2m1f_test.cpp
new file mode 100644
index 00000000000000..2111024cb5c03b
--- /dev/null
+++ b/libc/test/src/math/exhaustive/exp2m1f_test.cpp
@@ -0,0 +1,33 @@
+//===-- Exhaustive test for exp2m1f ---------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "exhaustive_test.h"
+#include "src/math/exp2m1f.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+
+namespace mpfr = LIBC_NAMESPACE::testing::mpfr;
+
+using LlvmLibcExp2m1fExhaustiveTest =
+    LlvmLibcUnaryOpExhaustiveMathTest<float, mpfr::Operation::Exp2m1,
+                                      LIBC_NAMESPACE::exp2m1f>;
+
+// Range: [0, Inf];
+static constexpr uint32_t POS_START = 0x0000'0000U;
+static constexpr uint32_t POS_STOP = 0x7f80'0000U;
+
+TEST_F(LlvmLibcExp2m1fExhaustiveTest, PostiveRange) {
+  test_full_range_all_roundings(POS_START, POS_STOP);
+}
+
+// Range: [-Inf, 0];
+static constexpr uint32_t NEG_START = 0x8000'0000U;
+static constexpr uint32_t NEG_STOP = 0xff80'0000U;
+
+TEST_F(LlvmLibcExp2m1fExhaustiveTest, NegativeRange) {
+  test_full_range_all_roundings(NEG_START, NEG_STOP);
+}
diff --git a/libc/test/src/math/smoke/CMakeLists.txt b/libc/test/src/math/smoke/CMakeLists.txt
index 3b756127fe21ea..d07927f5d5e4bf 100644
--- a/libc/test/src/math/smoke/CMakeLists.txt
+++ b/libc/test/src/math/smoke/CMakeLists.txt
@@ -769,6 +769,18 @@ add_fp_unittest(
    libc.src.__support.FPUtil.fp_bits
 )
 
+add_fp_unittest(
+  exp2m1f_test
+  SUITE
+    libc-math-smoke-tests
+  SRCS
+    exp2m1f_test.cpp
+  DEPENDS
+    libc.src.__support.FPUtil.fp_bits
+    libc.src.errno.errno
+    libc.src.math.exp2m1f
+)
+
 add_fp_unittest(
   exp10f_test
   SUITE
diff --git a/libc/test/src/math/smoke/exp2m1f_test.cpp b/libc/test/src/math/smoke/exp2m1f_test.cpp
new file mode 100644
index 00000000000000..1db865b91a0c26
--- /dev/null
+++ b/libc/test/src/math/smoke/exp2m1f_test.cpp
@@ -0,0 +1,57 @@
+//===-- Unittests for exp2m1f ---------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/errno/libc_errno.h"
+#include "src/math/exp2m1f.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+
+using LlvmLibcExp2m1fTest = LIBC_NAMESPACE::testing::FPTest<float>;
+
+TEST_F(LlvmLibcExp2m1fTest, SpecialNumbers) {
+  LIBC_NAMESPACE::libc_errno = 0;
+
+  EXPECT_FP_EQ_ALL_ROUNDING(aNaN, LIBC_NAMESPACE::exp2m1f(aNaN));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ_ALL_ROUNDING(inf, LIBC_NAMESPACE::exp2m1f(inf));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ_ALL_ROUNDING(-1.0f, LIBC_NAMESPACE::exp2m1f(neg_inf));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ_ALL_ROUNDING(0.0f, LIBC_NAMESPACE::exp2m1f(0.0f));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ_ALL_ROUNDING(-0.0f, LIBC_NAMESPACE::exp2m1f(-0.0f));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ_ALL_ROUNDING(1.0f, LIBC_NAMESPACE::exp2m1f(1.0f));
+  EXPECT_FP_EQ_ALL_ROUNDING(-0.5f, LIBC_NAMESPACE::exp2m1f(-1.0f));
+  EXPECT_FP_EQ_ALL_ROUNDING(3.0f, LIBC_NAMESPACE::exp2m1f(2.0f));
+  EXPECT_FP_EQ_ALL_ROUNDING(-0.75f, LIBC_NAMESPACE::exp2m1f(-2.0f));
+}
+
+TEST_F(LlvmLibcExp2m1fTest, Overflow) {
+  LIBC_NAMESPACE::libc_errno = 0;
+  EXPECT_FP_EQ_WITH_EXCEPTION(
+      inf, LIBC_NAMESPACE::exp2m1f(FPBits(0x7f7f'ffffU).get_val()),
+      FE_OVERFLOW);
+  EXPECT_MATH_ERRNO(ERANGE);
+
+  EXPECT_FP_EQ_WITH_EXCEPTION(
+      inf, LIBC_NAMESPACE::exp2m1f(FPBits(0x4300'0000U).get_val()),
+      FE_OVERFLOW);
+  EXPECT_MATH_ERRNO(ERANGE);
+
+  EXPECT_FP_EQ_WITH_EXCEPTION(
+      inf, LIBC_NAMESPACE::exp2m1f(FPBits(0x4300'0001U).get_val()),
+      FE_OVERFLOW);
+  EXPECT_MATH_ERRNO(ERANGE);
+}
diff --git a/libc/utils/MPFRWrapper/MPFRUtils.cpp b/libc/utils/MPFRWrapper/MPFRUtils.cpp
index 2e1c44e6fd5da9..d694d893b45aac 100644
--- a/libc/utils/MPFRWrapper/MPFRUtils.cpp
+++ b/libc/utils/MPFRWrapper/MPFRUtils.cpp
@@ -223,6 +223,12 @@ class MPFRNumber {
     return result;
   }
 
+  MPFRNumber exp2m1() const {
+    MPFRNumber result(*this);
+    mpfr_exp2m1(result.value, value, mpfr_rounding);
+    return result;
+  }
+
   MPFRNumber exp10() const {
     MPFRNumber result(*this);
     mpfr_exp10(result.value, value, mpfr_rounding);
@@ -564,6 +570,8 @@ unary_operation(Operation op, InputType input, unsigned int precision,
     return mpfrInput.exp();
   case Operation::Exp2:
     return mpfrInput.exp2();
+  case Operation::Exp2m1:
+    return mpfrInput.exp2m1();
   case Operation::Exp10:
     return mpfrInput.exp10();
   case Operation::Expm1:
diff --git a/libc/utils/MPFRWrapper/MPFRUtils.h b/libc/utils/MPFRWrapper/MPFRUtils.h
index 6164d78fa5adc4..66e83f6f0dcc34 100644
--- a/libc/utils/MPFRWrapper/MPFRUtils.h
+++ b/libc/utils/MPFRWrapper/MPFRUtils.h
@@ -37,6 +37,7 @@ enum class Operation : int {
   Erf,
   Exp,
   Exp2,
+  Exp2m1,
   Exp10,
   Expm1,
   Floor,

>From 5db48641785f8739f1df8d9fba500e15a4def2a2 Mon Sep 17 00:00:00 2001
From: OverMighty <its.overmighty at gmail.com>
Date: Fri, 29 Mar 2024 19:28:12 +0000
Subject: [PATCH 2/3] fixup! [libc][math][c23] Add exp2m1f C23 math function

---
 libc/docs/math/index.rst                  |  2 +
 libc/src/math/generic/exp2m1f.cpp         | 72 +++++++++++++++++------
 libc/test/src/math/CMakeLists.txt         | 16 +++++
 libc/test/src/math/exp2m1f_test.cpp       | 67 +++++++++++++++++++++
 libc/test/src/math/smoke/CMakeLists.txt   |  1 -
 libc/test/src/math/smoke/exp2m1f_test.cpp | 39 +++++++-----
 6 files changed, 165 insertions(+), 32 deletions(-)
 create mode 100644 libc/test/src/math/exp2m1f_test.cpp

diff --git a/libc/docs/math/index.rst b/libc/docs/math/index.rst
index 080b6a4427f511..02d3dbfd7ba3bf 100644
--- a/libc/docs/math/index.rst
+++ b/libc/docs/math/index.rst
@@ -480,6 +480,8 @@ Higher Math Functions
 +------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
 | exp2l      |         |         |         |         |         |         |         |         |         |         |         |         |
 +------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
+| exp2m1f    | |check| |         |         |         |         |         |         |         |         |         |         |         |
++------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
 | expm1      | |check| | |check| | |check| | |check| | |check| |         |         | |check| | |check| | |check| |         |         |
 +------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
 | expm1f     | |check| | |check| | |check| | |check| | |check| |         |         | |check| | |check| | |check| |         |         |
diff --git a/libc/src/math/generic/exp2m1f.cpp b/libc/src/math/generic/exp2m1f.cpp
index ea5c637b0b8692..3790171ed531eb 100644
--- a/libc/src/math/generic/exp2m1f.cpp
+++ b/libc/src/math/generic/exp2m1f.cpp
@@ -10,6 +10,7 @@
 #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"
@@ -21,6 +22,40 @@
 
 namespace LIBC_NAMESPACE {
 
+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 = 2;
+
+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},
+    }};
+
 LLVM_LIBC_FUNCTION(float, exp2m1f, (float x)) {
   using FPBits = fputil::FPBits<float>;
   FPBits xbits(x);
@@ -32,7 +67,8 @@ LLVM_LIBC_FUNCTION(float, exp2m1f, (float x)) {
   if (LIBC_UNLIKELY(x_abs >= 0x4300'0000U || x_abs <= 0x3d00'0000U)) {
     // |x| <= 2^-5
     if (x_abs <= 0x3d00'0000) {
-      // TODO: Handle exceptional values.
+      if (auto r = EXP2M1F_EXCEPTS_LO.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
+        return r.value();
 
       // Minimax polynomial generated by Sollya with:
       // > display = hexadecimal;
@@ -63,26 +99,28 @@ LLVM_LIBC_FUNCTION(float, exp2m1f, (float x)) {
       // x >= 128 and 2^x - 1 rounds to +inf, or x is +inf or nan
       return x + FPBits::inf().get_val();
     }
+  }
 
-    // x <= -25
-    if (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);
+  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;
   }
 
+  if (auto r = EXP2M1F_EXCEPTS_HI.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
+    return r.value();
+
   // 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:
diff --git a/libc/test/src/math/CMakeLists.txt b/libc/test/src/math/CMakeLists.txt
index 026bcd12928bdf..d27c3218416732 100644
--- a/libc/test/src/math/CMakeLists.txt
+++ b/libc/test/src/math/CMakeLists.txt
@@ -637,6 +637,22 @@ add_fp_unittest(
    libc.src.__support.FPUtil.fp_bits
 )
 
+add_fp_unittest(
+  exp2m1f_test
+  NEED_MPFR
+  SUITE
+    libc-math-unittests
+  SRCS
+    exp2m1f_test.cpp
+  DEPENDS
+    libc.include.llvm-libc-macros.math_macros
+    libc.include.llvm-libc-macros.stdint_macros
+    libc.src.errno.errno
+    libc.src.math.exp2m1f
+    libc.src.__support.CPP.array
+    libc.src.__support.FPUtil.fp_bits
+)
+
 add_fp_unittest(
   exp10f_test
   NEED_MPFR
diff --git a/libc/test/src/math/exp2m1f_test.cpp b/libc/test/src/math/exp2m1f_test.cpp
new file mode 100644
index 00000000000000..b35d94cb0f788d
--- /dev/null
+++ b/libc/test/src/math/exp2m1f_test.cpp
@@ -0,0 +1,67 @@
+//===-- Unittests for exp2m1f ---------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "include/llvm-libc-macros/math-macros.h"
+#include "src/__support/CPP/array.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/errno/libc_errno.h"
+#include "src/math/exp2m1f.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+
+#include <stdint.h>
+
+using LlvmLibcExp2m1fTest = LIBC_NAMESPACE::testing::FPTest<float>;
+
+namespace mpfr = LIBC_NAMESPACE::testing::mpfr;
+
+TEST_F(LlvmLibcExp2m1fTest, TrickyInputs) {
+  constexpr LIBC_NAMESPACE::cpp::array<float, 10> INPUTS = {
+      // EXP2M1F_EXCEPTS_LO
+      0x1.36dc8ep-36,
+      0x1.224936p-19,
+      0x1.d16d2p-20,
+      0x1.17949ep-14,
+      -0x1.9c3e1ep-38,
+      -0x1.4d89b4p-32,
+      -0x1.a6eac4p-10,
+      -0x1.e7526ep-6,
+      // EXP2M1F_EXCEPTS_HI
+      0x1.16a972p-1,
+      -0x1.9f12acp-5,
+  };
+
+  for (float x : INPUTS) {
+    LIBC_NAMESPACE::libc_errno = 0;
+    EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Exp2m1, x,
+                                   LIBC_NAMESPACE::exp2m1f(x), 0.5);
+    EXPECT_MATH_ERRNO(0);
+  }
+}
+
+TEST_F(LlvmLibcExp2m1fTest, InFloatRange) {
+  constexpr uint32_t COUNT = 100'000;
+  constexpr uint32_t STEP = UINT32_MAX / COUNT;
+  for (uint32_t i = 0, v = 0; i <= COUNT; ++i, v += STEP) {
+    float x = FPBits(v).get_val();
+    if (isnan(x) || isinf(x))
+      continue;
+    LIBC_NAMESPACE::libc_errno = 0;
+    float result = LIBC_NAMESPACE::exp2m1f(x);
+
+    // If the computation resulted in an error or did not produce valid result
+    // in the single-precision floating point range, then ignore comparing with
+    // MPFR result as MPFR can still produce valid results because of its
+    // wider precision.
+    if (isnan(result) || isinf(result) || LIBC_NAMESPACE::libc_errno != 0)
+      continue;
+    ASSERT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Exp2m1, x,
+                                   LIBC_NAMESPACE::exp2m1f(x), 0.5);
+  }
+}
diff --git a/libc/test/src/math/smoke/CMakeLists.txt b/libc/test/src/math/smoke/CMakeLists.txt
index d07927f5d5e4bf..c65d6339d6c671 100644
--- a/libc/test/src/math/smoke/CMakeLists.txt
+++ b/libc/test/src/math/smoke/CMakeLists.txt
@@ -776,7 +776,6 @@ add_fp_unittest(
   SRCS
     exp2m1f_test.cpp
   DEPENDS
-    libc.src.__support.FPUtil.fp_bits
     libc.src.errno.errno
     libc.src.math.exp2m1f
 )
diff --git a/libc/test/src/math/smoke/exp2m1f_test.cpp b/libc/test/src/math/smoke/exp2m1f_test.cpp
index 1db865b91a0c26..c144856b30b769 100644
--- a/libc/test/src/math/smoke/exp2m1f_test.cpp
+++ b/libc/test/src/math/smoke/exp2m1f_test.cpp
@@ -6,29 +6,26 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "src/__support/FPUtil/FPBits.h"
 #include "src/errno/libc_errno.h"
 #include "src/math/exp2m1f.h"
 #include "test/UnitTest/FPMatcher.h"
 #include "test/UnitTest/Test.h"
 
 using LlvmLibcExp2m1fTest = LIBC_NAMESPACE::testing::FPTest<float>;
+using LIBC_NAMESPACE::fputil::testing::ForceRoundingMode;
+using LIBC_NAMESPACE::fputil::testing::RoundingMode;
 
 TEST_F(LlvmLibcExp2m1fTest, SpecialNumbers) {
   LIBC_NAMESPACE::libc_errno = 0;
 
   EXPECT_FP_EQ_ALL_ROUNDING(aNaN, LIBC_NAMESPACE::exp2m1f(aNaN));
   EXPECT_MATH_ERRNO(0);
-
   EXPECT_FP_EQ_ALL_ROUNDING(inf, LIBC_NAMESPACE::exp2m1f(inf));
   EXPECT_MATH_ERRNO(0);
-
   EXPECT_FP_EQ_ALL_ROUNDING(-1.0f, LIBC_NAMESPACE::exp2m1f(neg_inf));
   EXPECT_MATH_ERRNO(0);
-
   EXPECT_FP_EQ_ALL_ROUNDING(0.0f, LIBC_NAMESPACE::exp2m1f(0.0f));
   EXPECT_MATH_ERRNO(0);
-
   EXPECT_FP_EQ_ALL_ROUNDING(-0.0f, LIBC_NAMESPACE::exp2m1f(-0.0f));
   EXPECT_MATH_ERRNO(0);
 
@@ -40,18 +37,32 @@ TEST_F(LlvmLibcExp2m1fTest, SpecialNumbers) {
 
 TEST_F(LlvmLibcExp2m1fTest, Overflow) {
   LIBC_NAMESPACE::libc_errno = 0;
-  EXPECT_FP_EQ_WITH_EXCEPTION(
-      inf, LIBC_NAMESPACE::exp2m1f(FPBits(0x7f7f'ffffU).get_val()),
-      FE_OVERFLOW);
+
+  EXPECT_FP_EQ_WITH_EXCEPTION(inf, LIBC_NAMESPACE::exp2m1f(0x1.fffffep+127),
+                              FE_OVERFLOW);
+  EXPECT_MATH_ERRNO(ERANGE);
+
+  EXPECT_FP_EQ_WITH_EXCEPTION(inf, LIBC_NAMESPACE::exp2m1f(128.0f),
+                              FE_OVERFLOW);
+  EXPECT_MATH_ERRNO(ERANGE);
+
+  EXPECT_FP_EQ_WITH_EXCEPTION(inf, LIBC_NAMESPACE::exp2m1f(0x1.000002p+7),
+                              FE_OVERFLOW);
+  EXPECT_MATH_ERRNO(ERANGE);
+}
+
+TEST_F(LlvmLibcExp2m1fTest, Underflow) {
+  LIBC_NAMESPACE::libc_errno = 0;
+
+  EXPECT_FP_EQ_WITH_EXCEPTION(-1.0f, LIBC_NAMESPACE::exp2m1f(-0x1.fffffep+127),
+                              FE_UNDERFLOW);
   EXPECT_MATH_ERRNO(ERANGE);
 
-  EXPECT_FP_EQ_WITH_EXCEPTION(
-      inf, LIBC_NAMESPACE::exp2m1f(FPBits(0x4300'0000U).get_val()),
-      FE_OVERFLOW);
+  EXPECT_FP_EQ_WITH_EXCEPTION(-1.0f, LIBC_NAMESPACE::exp2m1f(-25.0f),
+                              FE_UNDERFLOW);
   EXPECT_MATH_ERRNO(ERANGE);
 
-  EXPECT_FP_EQ_WITH_EXCEPTION(
-      inf, LIBC_NAMESPACE::exp2m1f(FPBits(0x4300'0001U).get_val()),
-      FE_OVERFLOW);
+  EXPECT_FP_EQ_WITH_EXCEPTION(-1.0f, LIBC_NAMESPACE::exp2m1f(-0x1.900002p4),
+                              FE_UNDERFLOW);
   EXPECT_MATH_ERRNO(ERANGE);
 }

>From 28a6b56a75333cc2be87d138487046f5f0b304b6 Mon Sep 17 00:00:00 2001
From: OverMighty <its.overmighty at gmail.com>
Date: Mon, 1 Apr 2024 01:38:51 +0100
Subject: [PATCH 3/3] fixup! [libc][math][c23] Add exp2m1f C23 math function

---
 libc/utils/MPFRWrapper/MPFRUtils.cpp | 37 +++++++++++++++++++++++++---
 1 file changed, 34 insertions(+), 3 deletions(-)

diff --git a/libc/utils/MPFRWrapper/MPFRUtils.cpp b/libc/utils/MPFRWrapper/MPFRUtils.cpp
index d694d893b45aac..50c51498304d50 100644
--- a/libc/utils/MPFRWrapper/MPFRUtils.cpp
+++ b/libc/utils/MPFRWrapper/MPFRUtils.cpp
@@ -134,6 +134,12 @@ class MPFRNumber {
     mpfr_set(value, other.value, mpfr_rounding);
   }
 
+  MPFRNumber(const MPFRNumber &other, unsigned int precision)
+      : mpfr_precision(precision), mpfr_rounding(other.mpfr_rounding) {
+    mpfr_init2(value, mpfr_precision);
+    mpfr_set(value, other.value, mpfr_rounding);
+  }
+
   ~MPFRNumber() { mpfr_clear(value); }
 
   MPFRNumber &operator=(const MPFRNumber &rhs) {
@@ -223,10 +229,28 @@ class MPFRNumber {
     return result;
   }
 
-  MPFRNumber exp2m1() const {
+  MPFRNumber
+  exp2m1([[maybe_unused]] const MPFRNumber &underflow_rndz_fallback) const {
+    // TODO: Only use mpfr_exp2m1 once CI and buildbots get MPFR >= 4.2.0.
+#if MPFR_VERSION_MAJOR > 4 ||                                                  \
+    (MPFR_VERSION_MAJOR == 4 && MPFR_VERSION_MINOR >= 2)
     MPFRNumber result(*this);
     mpfr_exp2m1(result.value, value, mpfr_rounding);
     return result;
+#else
+    MPFRNumber result(*this, mpfr_precision * 8);
+    mpfr_exp2(result.value, value, mpfr_rounding);
+
+    if (mpfr_underflow_p()) {
+      mpfr_clear_underflow();
+
+      if (mpfr_rounding == MPFR_RNDZ)
+        return underflow_rndz_fallback;
+    }
+
+    mpfr_sub_ui(result.value, result.value, 1, mpfr_rounding);
+    return result;
+#endif
   }
 
   MPFRNumber exp10() const {
@@ -570,8 +594,15 @@ unary_operation(Operation op, InputType input, unsigned int precision,
     return mpfrInput.exp();
   case Operation::Exp2:
     return mpfrInput.exp2();
-  case Operation::Exp2m1:
-    return mpfrInput.exp2m1();
+  case Operation::Exp2m1: {
+    constexpr InputType UNDERFLOW_RNDZ_FALLBACK =
+        FPBits<InputType>::create_value(Sign::NEG,
+                                        -1 + FPBits<InputType>::EXP_BIAS,
+                                        FPBits<InputType>::SIG_MASK)
+            .get_val();
+    MPFRNumber underflow_rndz_fallback(UNDERFLOW_RNDZ_FALLBACK);
+    return mpfrInput.exp2m1(underflow_rndz_fallback);
+  }
   case Operation::Exp10:
     return mpfrInput.exp10();
   case Operation::Expm1:



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