[libc-commits] [libc] [libc][math][c23] Add expm1f16 C23 math function (PR #102387)

via libc-commits libc-commits at lists.llvm.org
Wed Aug 7 14:55:10 PDT 2024


https://github.com/overmighty created https://github.com/llvm/llvm-project/pull/102387

Part of #95250.


>From eff043c923d4b3d243c3e8ec56d38b067850275a Mon Sep 17 00:00:00 2001
From: OverMighty <its.overmighty at gmail.com>
Date: Wed, 7 Aug 2024 23:50:26 +0200
Subject: [PATCH] [libc][math][c23] Add expm1f16 C23 math function

Part of #95250.
---
 libc/config/linux/x86_64/entrypoints.txt   |   1 +
 libc/docs/math/index.rst                   |   2 +-
 libc/spec/stdc.td                          |   1 +
 libc/src/math/CMakeLists.txt               |   1 +
 libc/src/math/expm1f16.h                   |  21 ++++
 libc/src/math/generic/CMakeLists.txt       |  28 ++++-
 libc/src/math/generic/expf16.cpp           |  61 +--------
 libc/src/math/generic/expm1f16.cpp         | 139 +++++++++++++++++++++
 libc/src/math/generic/expxf16.h            |  65 ++++++++++
 libc/test/src/math/CMakeLists.txt          |  31 +++--
 libc/test/src/math/expm1f16_test.cpp       |  40 ++++++
 libc/test/src/math/smoke/CMakeLists.txt    |  21 +++-
 libc/test/src/math/smoke/expm1f16_test.cpp |  65 ++++++++++
 13 files changed, 401 insertions(+), 75 deletions(-)
 create mode 100644 libc/src/math/expm1f16.h
 create mode 100644 libc/src/math/generic/expm1f16.cpp
 create mode 100644 libc/test/src/math/expm1f16_test.cpp
 create mode 100644 libc/test/src/math/smoke/expm1f16_test.cpp

diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 39d90bf06a0cf..332a90c84fbdc 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -584,6 +584,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
     libc.src.math.exp10f16
     libc.src.math.exp2f16
     libc.src.math.expf16
+    libc.src.math.expm1f16
     libc.src.math.f16add
     libc.src.math.f16addf
     libc.src.math.f16addl
diff --git a/libc/docs/math/index.rst b/libc/docs/math/index.rst
index ce83571e2b381..642776ddf4991 100644
--- a/libc/docs/math/index.rst
+++ b/libc/docs/math/index.rst
@@ -294,7 +294,7 @@ Higher Math Functions
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
 | exp2m1    | |check|          |                 |                        |                      |                        | 7.12.6.5               | F.10.3.5                   |
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
-| expm1     | |check|          | |check|         |                        |                      |                        | 7.12.6.6               | F.10.3.6                   |
+| expm1     | |check|          | |check|         |                        | |check|              |                        | 7.12.6.6               | F.10.3.6                   |
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
 | fma       | |check|          | |check|         |                        |                      |                        | 7.12.13.1              | F.10.10.1                  |
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
diff --git a/libc/spec/stdc.td b/libc/spec/stdc.td
index d24d43526fe5c..76555439a2dc8 100644
--- a/libc/spec/stdc.td
+++ b/libc/spec/stdc.td
@@ -594,6 +594,7 @@ def StdC : StandardSpec<"stdc"> {
 
           FunctionSpec<"expm1", RetValSpec<DoubleType>, [ArgSpec<DoubleType>]>,
           FunctionSpec<"expm1f", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
+          GuardedFunctionSpec<"expm1f16", RetValSpec<Float16Type>, [ArgSpec<Float16Type>], "LIBC_TYPES_HAS_FLOAT16">,
 
           FunctionSpec<"exp10", RetValSpec<DoubleType>, [ArgSpec<DoubleType>]>,
           FunctionSpec<"exp10f", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
diff --git a/libc/src/math/CMakeLists.txt b/libc/src/math/CMakeLists.txt
index a3c9b5473c290..9ccc3f1a347f2 100644
--- a/libc/src/math/CMakeLists.txt
+++ b/libc/src/math/CMakeLists.txt
@@ -120,6 +120,7 @@ add_math_entrypoint_object(exp10f16)
 
 add_math_entrypoint_object(expm1)
 add_math_entrypoint_object(expm1f)
+add_math_entrypoint_object(expm1f16)
 
 add_math_entrypoint_object(f16add)
 add_math_entrypoint_object(f16addf)
diff --git a/libc/src/math/expm1f16.h b/libc/src/math/expm1f16.h
new file mode 100644
index 0000000000000..644e6cddd7666
--- /dev/null
+++ b/libc/src/math/expm1f16.h
@@ -0,0 +1,21 @@
+//===-- Implementation header for expm1f16 ----------------------*- 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_EXPM1F16_H
+#define LLVM_LIBC_SRC_MATH_EXPM1F16_H
+
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/properties/types.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+float16 expm1f16(float16 x);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_MATH_EXPM1F16_H
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index 77f7f4fef007b..469df67951ab3 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -1322,14 +1322,12 @@ add_entrypoint_object(
   HDRS
     ../expf16.h
   DEPENDS
+    .expxf16
     libc.hdr.errno_macros
     libc.hdr.fenv_macros
-    libc.src.__support.CPP.array
     libc.src.__support.FPUtil.except_value_utils
     libc.src.__support.FPUtil.fenv_impl
     libc.src.__support.FPUtil.fp_bits
-    libc.src.__support.FPUtil.multiply_add
-    libc.src.__support.FPUtil.nearest_integer
     libc.src.__support.FPUtil.polyeval
     libc.src.__support.FPUtil.rounding_mode
     libc.src.__support.macros.optimization
@@ -1571,6 +1569,27 @@ add_entrypoint_object(
     -O3
 )
 
+add_entrypoint_object(
+  expm1f16
+  SRCS
+    expm1f16.cpp
+  HDRS
+    ../expm1f16.h
+  DEPENDS
+    .expxf16
+    libc.hdr.errno_macros
+    libc.hdr.fenv_macros
+    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
+  COMPILE_OPTIONS
+    -O3
+)
+
 add_entrypoint_object(
   powf
   SRCS
@@ -4878,4 +4897,7 @@ add_header_library(
     expxf16.h
   DEPENDS
     libc.src.__support.CPP.array
+    libc.src.__support.FPUtil.multiply_add
+    libc.src.__support.FPUtil.nearest_integer
+    libc.src.__support.FPUtil.polyeval
 )
diff --git a/libc/src/math/generic/expf16.cpp b/libc/src/math/generic/expf16.cpp
index b198c559dfedb..7ffdbd5191008 100644
--- a/libc/src/math/generic/expf16.cpp
+++ b/libc/src/math/generic/expf16.cpp
@@ -7,15 +7,13 @@
 //===----------------------------------------------------------------------===//
 
 #include "src/math/expf16.h"
+#include "expxf16.h"
 #include "hdr/errno_macros.h"
 #include "hdr/fenv_macros.h"
-#include "src/__support/CPP/array.h"
 #include "src/__support/FPUtil/FEnvImpl.h"
 #include "src/__support/FPUtil/FPBits.h"
 #include "src/__support/FPUtil/PolyEval.h"
 #include "src/__support/FPUtil/except_value_utils.h"
-#include "src/__support/FPUtil/multiply_add.h"
-#include "src/__support/FPUtil/nearest_integer.h"
 #include "src/__support/FPUtil/rounding_mode.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"
@@ -41,28 +39,6 @@ static constexpr fputil::ExceptValues<float16, 3> EXPF16_EXCEPTS_HI = {{
     {0xa954U, 0x3bacU, 1U, 0U, 0U},
 }};
 
-// Generated by Sollya with the following commands:
-//   > display = hexadecimal;
-//   > for i from -18 to 12 do print(round(exp(i), SG, RN));
-static constexpr cpp::array<float, 31> EXP_HI = {
-    0x1.05a628p-26f, 0x1.639e32p-25f, 0x1.e355bcp-24f, 0x1.4875cap-22f,
-    0x1.be6c7p-21f,  0x1.2f6054p-19f, 0x1.9c54c4p-18f, 0x1.183542p-16f,
-    0x1.7cd79cp-15f, 0x1.02cf22p-13f, 0x1.5fc21p-12f,  0x1.de16bap-11f,
-    0x1.44e52p-9f,   0x1.b993fep-8f,  0x1.2c155cp-6f,  0x1.97db0cp-5f,
-    0x1.152aaap-3f,  0x1.78b564p-2f,  0x1p+0f,         0x1.5bf0a8p+1f,
-    0x1.d8e64cp+2f,  0x1.415e5cp+4f,  0x1.b4c902p+5f,  0x1.28d38ap+7f,
-    0x1.936dc6p+8f,  0x1.122886p+10f, 0x1.749ea8p+11f, 0x1.fa7158p+12f,
-    0x1.5829dcp+14f, 0x1.d3c448p+15f, 0x1.3de166p+17f,
-};
-
-// Generated by Sollya with the following commands:
-//   > display = hexadecimal;
-//   > for i from 0 to 7 do print(round(exp(i * 2^-3), SG, RN));
-static constexpr cpp::array<float, 8> EXP_MID = {
-    0x1p+0f,        0x1.221604p+0f, 0x1.48b5e4p+0f, 0x1.747a52p+0f,
-    0x1.a61298p+0f, 0x1.de455ep+0f, 0x1.0ef9dcp+1f, 0x1.330e58p+1f,
-};
-
 LLVM_LIBC_FUNCTION(float16, expf16, (float16 x)) {
   using FPBits = fputil::FPBits<float16>;
   FPBits x_bits(x);
@@ -135,38 +111,9 @@ LLVM_LIBC_FUNCTION(float16, expf16, (float16 x)) {
   if (auto r = EXPF16_EXCEPTS_HI.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
     return r.value();
 
-  // For -18 < x < 12, 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 * 2^3 is an integer,
-  //     -2^(-4) <= lo < 2^(-4).
-  // In particular,
-  //   hi + mid = round(x * 2^3) * 2^(-3).
-  // 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_HI and EXP_MID
-  // respectively.  exp(lo) is computed using a degree-3 minimax polynomial
-  // generated by Sollya.
-
-  float xf = x;
-  float kf = fputil::nearest_integer(xf * 0x1.0p+3f);
-  int x_hi_mid = static_cast<int>(kf);
-  int x_hi = x_hi_mid >> 3;
-  int x_mid = x_hi_mid & 0x7;
-  // lo = x - (hi + mid) = round(x * 2^3) * (-2^(-3)) + x
-  float lo = fputil::multiply_add(kf, -0x1.0p-3f, xf);
-
-  float exp_hi = EXP_HI[x_hi + 18];
-  float exp_mid = EXP_MID[x_mid];
-  // Degree-3 minimax polynomial generated by Sollya with the following
-  // commands:
-  //   > display = hexadecimal;
-  //   > P = fpminimax(expm1(x)/x, 2, [|SG...|], [-2^-4, 2^-4]);
-  //   > 1 + x * P;
-  float exp_lo =
-      fputil::polyeval(lo, 0x1p+0f, 0x1p+0f, 0x1.001p-1f, 0x1.555ddep-3f);
-  return static_cast<float16>(exp_hi * exp_mid * exp_lo);
+  // exp(x) = exp(hi + mid) * exp(lo)
+  auto [exp_hi_mid, exp_lo] = exp_range_reduction(x);
+  return static_cast<float16>(exp_hi_mid * exp_lo);
 }
 
 } // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/math/generic/expm1f16.cpp b/libc/src/math/generic/expm1f16.cpp
new file mode 100644
index 0000000000000..f13f6850db524
--- /dev/null
+++ b/libc/src/math/generic/expm1f16.cpp
@@ -0,0 +1,139 @@
+//===-- Half-precision e^x - 1 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/expm1f16.h"
+#include "expxf16.h"
+#include "hdr/errno_macros.h"
+#include "hdr/fenv_macros.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/macros/config.h"
+#include "src/__support/macros/optimization.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+static constexpr fputil::ExceptValues<float16, 1> EXPM1F16_EXCEPTS_LO = {{
+    // (input, RZ output, RU offset, RD offset, RN offset)
+    // x = 0x1.564p-5, expm1f16(x) = 0x1.5d4p-5 (RZ)
+    {0x2959U, 0x2975U, 1U, 0U, 1U},
+}};
+
+#ifdef LIBC_TARGET_CPU_HAS_FMA
+static constexpr size_t N_EXPM1F16_EXCEPTS_HI = 2;
+#else
+static constexpr size_t N_EXPM1F16_EXCEPTS_HI = 3;
+#endif
+
+static constexpr fputil::ExceptValues<float16, N_EXPM1F16_EXCEPTS_HI>
+    EXPM1F16_EXCEPTS_HI = {{
+        // (input, RZ output, RU offset, RD offset, RN offset)
+        // x = 0x1.c34p+0, expm1f16(x) = 0x1.34cp+2 (RZ)
+        {0x3f0dU, 0x44d3U, 1U, 0U, 1U},
+        // x = -0x1.e28p-3, expm1f16(x) = -0x1.adcp-3 (RZ)
+        {0xb38aU, 0xb2b7U, 0U, 1U, 1U},
+#ifndef LIBC_TARGET_CPU_HAS_FMA
+        // x = 0x1.a08p-3, exp10m1f(x) = 0x1.cdcp-3 (RZ)
+        {0x3282U, 0x3337U, 1U, 0U, 0U},
+#endif
+    }};
+
+LLVM_LIBC_FUNCTION(float16, expm1f16, (float16 x)) {
+  using FPBits = fputil::FPBits<float16>;
+  FPBits x_bits(x);
+
+  uint16_t x_u = x_bits.uintval();
+  uint16_t x_abs = x_u & 0x7fffU;
+
+  // When |x| <= 2^(-3), or |x| >= -11 * log(2), or x is NaN.
+  if (LIBC_UNLIKELY(x_abs <= 0x3000U || x_abs >= 0x47a0U)) {
+    // expm1(NaN) = NaN
+    if (x_bits.is_nan()) {
+      if (x_bits.is_signaling_nan()) {
+        fputil::raise_except_if_required(FE_INVALID);
+        return FPBits::quiet_nan().get_val();
+      }
+
+      return x;
+    }
+
+    // expm1(+/-0) = +/-0
+    if (x_abs == 0)
+      return x;
+
+    // When x >= 12.
+    if (x_bits.is_pos() && x_abs >= 0x4a00U) {
+      // expm1(+inf) = +inf
+      if (x_bits.is_inf())
+        return FPBits::inf().get_val();
+
+      switch (fputil::quick_get_round()) {
+      case FE_TONEAREST:
+      case FE_UPWARD:
+        fputil::set_errno_if_required(ERANGE);
+        fputil::raise_except_if_required(FE_OVERFLOW);
+        return FPBits::inf().get_val();
+      default:
+        return FPBits::max_normal().get_val();
+      }
+    }
+
+    // When x <= -11 * log(2).
+    if (x_u >= 0xc7a0U) {
+      // expm1(-inf) = -1
+      if (x_bits.is_inf())
+        return FPBits::one(Sign::NEG).get_val();
+
+      fputil::set_errno_if_required(ERANGE);
+      fputil::raise_except_if_required(FE_INEXACT);
+
+      switch (fputil::quick_get_round()) {
+      case FE_UPWARD:
+      case FE_TOWARDZERO:
+        return static_cast<float16>(-0x1.ffcp-1);
+      case FE_TONEAREST:
+        if (x_u > 0xc828U)
+          return FPBits::one(Sign::NEG).get_val();
+        return static_cast<float16>(-0x1.ffcp-1);
+      default:
+        return FPBits::one(Sign::NEG).get_val();
+      }
+    }
+
+    // When 0 < |x| <= 2^(-3).
+    if (x_abs <= 0x3000U && !x_bits.is_zero()) {
+      if (auto r = EXPM1F16_EXCEPTS_LO.lookup(x_u);
+          LIBC_UNLIKELY(r.has_value()))
+        return r.value();
+
+      float xf = x;
+      // Degree-5 minimax polynomial generated by Sollya with the following
+      // commands:
+      //   > display = hexadecimal;
+      //   > P = fpminimax(expm1(x)/x, 4, [|SG...|], [-2^-3, 2^-3]);
+      //   > x * P;
+      return static_cast<float16>(
+          xf * fputil::polyeval(xf, 0x1p+0f, 0x1.fffff8p-2f, 0x1.555556p-3f,
+                                0x1.55905ep-5f, 0x1.1124c2p-7f));
+    }
+  }
+
+  if (auto r = EXPM1F16_EXCEPTS_HI.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
+    return r.value();
+
+  // exp(x) = exp(hi + mid) * exp(lo)
+  auto [exp_hi_mid, exp_lo] = exp_range_reduction(x);
+  // expm1(x) = exp(hi + mid) * exp(lo) - 1
+  return static_cast<float16>(fputil::multiply_add(exp_hi_mid, exp_lo, -1.0f));
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/src/math/generic/expxf16.h b/libc/src/math/generic/expxf16.h
index c33aca337b98d..53815e0e27553 100644
--- a/libc/src/math/generic/expxf16.h
+++ b/libc/src/math/generic/expxf16.h
@@ -10,11 +10,76 @@
 #define LLVM_LIBC_SRC_MATH_GENERIC_EXPXF16_H
 
 #include "src/__support/CPP/array.h"
+#include "src/__support/FPUtil/PolyEval.h"
+#include "src/__support/FPUtil/multiply_add.h"
+#include "src/__support/FPUtil/nearest_integer.h"
 #include "src/__support/macros/config.h"
 #include <stdint.h>
 
 namespace LIBC_NAMESPACE_DECL {
 
+// Generated by Sollya with the following commands:
+//   > display = hexadecimal;
+//   > for i from -18 to 12 do print(round(exp(i), SG, RN));
+static constexpr cpp::array<float, 31> EXP_HI = {
+    0x1.05a628p-26f, 0x1.639e32p-25f, 0x1.e355bcp-24f, 0x1.4875cap-22f,
+    0x1.be6c7p-21f,  0x1.2f6054p-19f, 0x1.9c54c4p-18f, 0x1.183542p-16f,
+    0x1.7cd79cp-15f, 0x1.02cf22p-13f, 0x1.5fc21p-12f,  0x1.de16bap-11f,
+    0x1.44e52p-9f,   0x1.b993fep-8f,  0x1.2c155cp-6f,  0x1.97db0cp-5f,
+    0x1.152aaap-3f,  0x1.78b564p-2f,  0x1p+0f,         0x1.5bf0a8p+1f,
+    0x1.d8e64cp+2f,  0x1.415e5cp+4f,  0x1.b4c902p+5f,  0x1.28d38ap+7f,
+    0x1.936dc6p+8f,  0x1.122886p+10f, 0x1.749ea8p+11f, 0x1.fa7158p+12f,
+    0x1.5829dcp+14f, 0x1.d3c448p+15f, 0x1.3de166p+17f,
+};
+
+// Generated by Sollya with the following commands:
+//   > display = hexadecimal;
+//   > for i from 0 to 7 do print(round(exp(i * 2^-3), SG, RN));
+static constexpr cpp::array<float, 8> EXP_MID = {
+    0x1p+0f,        0x1.221604p+0f, 0x1.48b5e4p+0f, 0x1.747a52p+0f,
+    0x1.a61298p+0f, 0x1.de455ep+0f, 0x1.0ef9dcp+1f, 0x1.330e58p+1f,
+};
+
+struct ExpRangeReduction {
+  float exp_hi_mid;
+  float exp_lo;
+};
+
+ExpRangeReduction exp_range_reduction(float16 x) {
+  // For -18 < x < 12, 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 * 2^3 is an integer,
+  //     -2^(-4) <= lo < 2^(-4).
+  // In particular,
+  //   hi + mid = round(x * 2^3) * 2^(-3).
+  // 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_HI and EXP_MID
+  // respectively.  exp(lo) is computed using a degree-3 minimax polynomial
+  // generated by Sollya.
+
+  float xf = x;
+  float kf = fputil::nearest_integer(xf * 0x1.0p+3f);
+  int x_hi_mid = static_cast<int>(kf);
+  int x_hi = x_hi_mid >> 3;
+  int x_mid = x_hi_mid & 0x7;
+  // lo = x - (hi + mid) = round(x * 2^3) * (-2^(-3)) + x
+  float lo = fputil::multiply_add(kf, -0x1.0p-3f, xf);
+
+  float exp_hi = EXP_HI[x_hi + 18];
+  float exp_mid = EXP_MID[x_mid];
+  // Degree-3 minimax polynomial generated by Sollya with the following
+  // commands:
+  //   > display = hexadecimal;
+  //   > P = fpminimax(expm1(x)/x, 2, [|SG...|], [-2^-4, 2^-4]);
+  //   > 1 + x * P;
+  float exp_lo =
+      fputil::polyeval(lo, 0x1p+0f, 0x1p+0f, 0x1.001p-1f, 0x1.555ddep-3f);
+  return {exp_hi * exp_mid, exp_lo};
+}
+
 // Generated by Sollya with the following commands:
 //   > display = hexadecimal;
 //   > for i from 0 to 7 do printsingle(round(2^(i * 2^-3), SG, RN));
diff --git a/libc/test/src/math/CMakeLists.txt b/libc/test/src/math/CMakeLists.txt
index d209c9a38499b..b6b6953a68871 100644
--- a/libc/test/src/math/CMakeLists.txt
+++ b/libc/test/src/math/CMakeLists.txt
@@ -1663,6 +1663,19 @@ add_fp_unittest(
     libc.src.__support.FPUtil.fp_bits
 )
 
+add_fp_unittest(
+  expm1_test
+  NEED_MPFR
+  SUITE
+    libc-math-unittests
+  SRCS
+    expm1_test.cpp
+  DEPENDS
+    libc.src.errno.errno
+    libc.src.math.expm1
+    libc.src.__support.FPUtil.fp_bits
+)
+
 add_fp_unittest(
   expm1f_test
   NEED_MPFR
@@ -1677,16 +1690,14 @@ add_fp_unittest(
 )
 
 add_fp_unittest(
- expm1_test
- NEED_MPFR
- SUITE
-   libc-math-unittests
- SRCS
-   expm1_test.cpp
- DEPENDS
-   libc.src.errno.errno
-   libc.src.math.expm1
-   libc.src.__support.FPUtil.fp_bits
+  expm1f16_test
+  NEED_MPFR
+  SUITE
+    libc-math-unittests
+  SRCS
+    expm1f16_test.cpp
+  DEPENDS
+    libc.src.math.expm1f16
 )
 
 add_fp_unittest(
diff --git a/libc/test/src/math/expm1f16_test.cpp b/libc/test/src/math/expm1f16_test.cpp
new file mode 100644
index 0000000000000..a6a6fcf73d383
--- /dev/null
+++ b/libc/test/src/math/expm1f16_test.cpp
@@ -0,0 +1,40 @@
+//===-- Exhaustive test for expm1f16 --------------------------------------===//
+//
+// 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/expm1f16.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+
+using LlvmLibcExpm1f16Test = LIBC_NAMESPACE::testing::FPTest<float16>;
+
+namespace mpfr = LIBC_NAMESPACE::testing::mpfr;
+
+// Range: [0, Inf];
+static constexpr uint16_t POS_START = 0x0000U;
+static constexpr uint16_t POS_STOP = 0x7c00U;
+
+// Range: [-Inf, 0];
+static constexpr uint16_t NEG_START = 0x8000U;
+static constexpr uint16_t NEG_STOP = 0xfc00U;
+
+TEST_F(LlvmLibcExpm1f16Test, PositiveRange) {
+  for (uint16_t v = POS_START; v <= POS_STOP; ++v) {
+    float16 x = FPBits(v).get_val();
+    EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Expm1, x,
+                                   LIBC_NAMESPACE::expm1f16(x), 0.5);
+  }
+}
+
+TEST_F(LlvmLibcExpm1f16Test, NegativeRange) {
+  for (uint16_t v = NEG_START; v <= NEG_STOP; ++v) {
+    float16 x = FPBits(v).get_val();
+    EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Expm1, x,
+                                   LIBC_NAMESPACE::expm1f16(x), 0.5);
+  }
+}
diff --git a/libc/test/src/math/smoke/CMakeLists.txt b/libc/test/src/math/smoke/CMakeLists.txt
index 9aa5399aae9d3..18d8eb27aec23 100644
--- a/libc/test/src/math/smoke/CMakeLists.txt
+++ b/libc/test/src/math/smoke/CMakeLists.txt
@@ -3294,6 +3294,18 @@ add_fp_unittest(
     libc.src.math.fma
 )
 
+add_fp_unittest(
+  expm1_test
+  SUITE
+    libc-math-smoke-tests
+  SRCS
+    expm1_test.cpp
+  DEPENDS
+    libc.src.errno.errno
+    libc.src.math.expm1
+    libc.src.__support.FPUtil.fp_bits
+)
+
 add_fp_unittest(
   expm1f_test
   SUITE
@@ -3307,15 +3319,16 @@ add_fp_unittest(
 )
 
 add_fp_unittest(
-  expm1_test
+  expm1f16_test
   SUITE
     libc-math-smoke-tests
   SRCS
-    expm1_test.cpp
+    expm1f16_test.cpp
   DEPENDS
+    libc.hdr.errno_macros
+    libc.hdr.fenv_macros
     libc.src.errno.errno
-    libc.src.math.expm1
-    libc.src.__support.FPUtil.fp_bits
+    libc.src.math.expm1f16
 )
 
 add_fp_unittest(
diff --git a/libc/test/src/math/smoke/expm1f16_test.cpp b/libc/test/src/math/smoke/expm1f16_test.cpp
new file mode 100644
index 0000000000000..959fa517a5046
--- /dev/null
+++ b/libc/test/src/math/smoke/expm1f16_test.cpp
@@ -0,0 +1,65 @@
+//===-- Unittests for expm1f16 --------------------------------------------===//
+//
+// 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 "hdr/errno_macros.h"
+#include "hdr/fenv_macros.h"
+#include "src/errno/libc_errno.h"
+#include "src/math/expm1f16.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+
+using LlvmLibcExpm1f16Test = LIBC_NAMESPACE::testing::FPTest<float16>;
+
+TEST_F(LlvmLibcExpm1f16Test, SpecialNumbers) {
+  LIBC_NAMESPACE::libc_errno = 0;
+
+  EXPECT_FP_EQ_ALL_ROUNDING(aNaN, LIBC_NAMESPACE::expm1f16(aNaN));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ_WITH_EXCEPTION(aNaN, LIBC_NAMESPACE::expm1f16(sNaN), FE_INVALID);
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ_ALL_ROUNDING(inf, LIBC_NAMESPACE::expm1f16(inf));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ_ALL_ROUNDING(static_cast<float16>(-1.0),
+                            LIBC_NAMESPACE::expm1f16(neg_inf));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ_ALL_ROUNDING(zero, LIBC_NAMESPACE::expm1f16(zero));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ_ALL_ROUNDING(neg_zero, LIBC_NAMESPACE::expm1f16(neg_zero));
+  EXPECT_MATH_ERRNO(0);
+}
+
+TEST_F(LlvmLibcExpm1f16Test, Overflow) {
+  LIBC_NAMESPACE::libc_errno = 0;
+
+  EXPECT_FP_EQ_WITH_EXCEPTION(inf, LIBC_NAMESPACE::expm1f16(max_normal),
+                              FE_OVERFLOW);
+  EXPECT_MATH_ERRNO(ERANGE);
+
+  EXPECT_FP_EQ_WITH_EXCEPTION(
+      inf, LIBC_NAMESPACE::expm1f16(static_cast<float16>(12.0)), FE_OVERFLOW);
+  EXPECT_MATH_ERRNO(ERANGE);
+}
+
+TEST_F(LlvmLibcExpm1f16Test, ResultNearNegOne) {
+  LIBC_NAMESPACE::libc_errno = 0;
+
+  EXPECT_FP_EQ_WITH_EXCEPTION(static_cast<float16>(-1.0),
+                              LIBC_NAMESPACE::expm1f16(neg_max_normal),
+                              FE_INEXACT);
+  EXPECT_MATH_ERRNO(ERANGE);
+
+  EXPECT_FP_EQ_WITH_EXCEPTION(
+      static_cast<float16>(-1.0),
+      LIBC_NAMESPACE::expm1f16(static_cast<float16>(-9.0)), FE_INEXACT);
+  EXPECT_MATH_ERRNO(ERANGE);
+}



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