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

libc/shared/math.h

@@ -51,6 +51,7 @@
 #include "math/exp2f.h"
 #include "math/exp2f16.h"
 #include "math/exp2m1f.h"
+#include "math/exp2m1f16.h"
 #include "math/expf.h"
 #include "math/expf16.h"
 #include "math/frexpf.h"

libc/shared/math/exp2m1f16.h

@@ -0,0 +1,29 @@
+//===-- Shared exp2m1f16 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_EXP2M1F16_H
+#define LLVM_LIBC_SHARED_MATH_EXP2M1F16_H
+
+#include "include/llvm-libc-macros/float16-macros.h"
+#include "shared/libc_common.h"
+
+#ifdef LIBC_TYPES_HAS_FLOAT16
+
+#include "src/__support/math/exp2m1f16.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace shared {
+
+using math::exp2m1f16;
+
+} // namespace shared
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_TYPES_HAS_FLOAT16
+
+#endif // LLVM_LIBC_SHARED_MATH_EXP2M1F16_H

libc/src/__support/math/CMakeLists.txt

@@ -785,6 +785,24 @@ add_header_library(
     libc.src.__support.macros.properties.cpu_features
 )
 
+add_header_library(
+  exp2m1f16
+  HDRS
+    exp2m1f16.h
+  DEPENDS
+    .expxf16_utils
+    libc.src.__support.common
+    libc.src.__support.FPUtil.cast
+    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

libc/src/__support/math/exp2m1f16.h

@@ -0,0 +1,180 @@
+//===-- Implementation header for exp2m1f16 ----------------------*- 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_EXP2M1F16_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_EXP2M1F16_H
+
+#include "include/llvm-libc-macros/float16-macros.h"
+
+#ifdef LIBC_TYPES_HAS_FLOAT16
+
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/PolyEval.h"
+#include "src/__support/FPUtil/cast.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/macros/config.h"
+#include "src/__support/macros/optimization.h"
+#include "src/__support/macros/properties/cpu_features.h"
+#include "src/__support/math/expxf16_utils.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+LIBC_INLINE static constexpr float16 exp2m1f16(float16 x) {
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+  constexpr fputil::ExceptValues<float16, 6> EXP2M1F16_EXCEPTS_LO = {{
+      // (input, RZ output, RU offset, RD offset, RN offset)
+      // x = 0x1.cf4p-13, exp2m1f16(x) = 0x1.41p-13 (RZ)
+      {0x0b3dU, 0x0904U, 1U, 0U, 1U},
+      // x = 0x1.4fcp-12, exp2m1f16(x) = 0x1.d14p-13 (RZ)
+      {0x0d3fU, 0x0b45U, 1U, 0U, 1U},
+      // x = 0x1.63p-11, exp2m1f16(x) = 0x1.ec4p-12 (RZ)
+      {0x118cU, 0x0fb1U, 1U, 0U, 0U},
+      // x = 0x1.6fp-7, exp2m1f16(x) = 0x1.fe8p-8 (RZ)
+      {0x21bcU, 0x1ffaU, 1U, 0U, 1U},
+      // x = -0x1.c6p-10, exp2m1f16(x) = -0x1.3a8p-10 (RZ)
+      {0x9718U, 0x94eaU, 0U, 1U, 0U},
+      // x = -0x1.cfcp-10, exp2m1f16(x) = -0x1.414p-10 (RZ)
+      {0x973fU, 0x9505U, 0U, 1U, 0U},
+  }};
+
+#ifdef LIBC_TARGET_CPU_HAS_FMA_FLOAT
+  constexpr size_t N_EXP2M1F16_EXCEPTS_HI = 6;
+#else
+  constexpr size_t N_EXP2M1F16_EXCEPTS_HI = 7;
+#endif
+
+  constexpr fputil::ExceptValues<float16, N_EXP2M1F16_EXCEPTS_HI>
+      EXP2M1F16_EXCEPTS_HI = {{
+          // (input, RZ output, RU offset, RD offset, RN offset)
+          // x = 0x1.e58p-3, exp2m1f16(x) = 0x1.6dcp-3 (RZ)
+          {0x3396U, 0x31b7U, 1U, 0U, 0U},
+#ifndef LIBC_TARGET_CPU_HAS_FMA_FLOAT
+          // x = 0x1.2e8p-2, exp2m1f16(x) = 0x1.d14p-3 (RZ)
+          {0x34baU, 0x3345U, 1U, 0U, 0U},
+#endif
+          // x = 0x1.ad8p-2, exp2m1f16(x) = 0x1.598p-2 (RZ)
+          {0x36b6U, 0x3566U, 1U, 0U, 0U},
+#ifdef LIBC_TARGET_CPU_HAS_FMA_FLOAT
+          // x = 0x1.edcp-2, exp2m1f16(x) = 0x1.964p-2 (RZ)
+          {0x37b7U, 0x3659U, 1U, 0U, 1U},
+#endif
+          // x = -0x1.804p-3, exp2m1f16(x) = -0x1.f34p-4 (RZ)
+          {0xb201U, 0xafcdU, 0U, 1U, 1U},
+          // x = -0x1.f3p-3, exp2m1f16(x) = -0x1.3e4p-3 (RZ)
+          {0xb3ccU, 0xb0f9U, 0U, 1U, 0U},
+          // x = -0x1.294p-1, exp2m1f16(x) = -0x1.53p-2 (RZ)
+          {0xb8a5U, 0xb54cU, 0U, 1U, 1U},
+#ifndef LIBC_TARGET_CPU_HAS_FMA_FLOAT
+          // x = -0x1.a34p-1, exp2m1f16(x) = -0x1.bb4p-2 (RZ)
+          {0xba8dU, 0xb6edU, 0U, 1U, 1U},
+#endif
+      }};
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+  using namespace math::expxf16_internal;
+  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, or x is NaN.
+  if (LIBC_UNLIKELY(x_abs <= 0x3000U || x_abs >= 0x4980U)) {
+    // exp2m1(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;
+    }
+
+    // When x >= 16.
+    if (x_u >= 0x4c00 && x_bits.is_pos()) {
+      // exp2m1(+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 | FE_INEXACT);
+        return FPBits::inf().get_val();
+      default:
+        return FPBits::max_normal().get_val();
+      }
+    }
+
+    // When x < -11.
+    if (x_u > 0xc980U) {
+      // exp2m1(-inf) = -1
+      if (x_bits.is_inf())
+        return FPBits::one(Sign::NEG).get_val();
+
+      // When -12 < x < -11, round(2^x - 1, HP, RN) = -0x1.ffcp-1.
+      if (x_u < 0xca00U)
+        return fputil::round_result_slightly_down(
+            fputil::cast<float16>(-0x1.ffcp-1));
+
+      // When x <= -12, round(2^x - 1, HP, RN) = -1.
+      switch (fputil::quick_get_round()) {
+      case FE_TONEAREST:
+      case FE_DOWNWARD:
+        return FPBits::one(Sign::NEG).get_val();
+      default:
+        return fputil::cast<float16>(-0x1.ffcp-1);
+      }
+    }
+
+    // When |x| <= 2^(-3).
+    if (x_abs <= 0x3000U) {
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+      if (auto r = EXP2M1F16_EXCEPTS_LO.lookup(x_u);
+          LIBC_UNLIKELY(r.has_value()))
+        return r.value();
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+      float xf = x;
+      // Degree-5 minimax polynomial generated by Sollya with the following
+      // commands:
+      //   > display = hexadecimal;
+      //   > P = fpminimax((2^x - 1)/x, 4, [|SG...|], [-2^-3, 2^-3]);
+      //   > x * P;
+      return fputil::cast<float16>(
+          xf * fputil::polyeval(xf, 0x1.62e43p-1f, 0x1.ebfbdep-3f,
+                                0x1.c6af88p-5f, 0x1.3b45d6p-7f,
+                                0x1.641e7cp-10f));
+    }
+  }
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+  if (auto r = EXP2M1F16_EXCEPTS_HI.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
+    return r.value();
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+  // exp2(x) = exp2(hi + mid) * exp2(lo)
+  auto [exp2_hi_mid, exp2_lo] = exp2_range_reduction(x);
+  // exp2m1(x) = exp2(hi + mid) * exp2(lo) - 1
+  return fputil::cast<float16>(
+      fputil::multiply_add(exp2_hi_mid, exp2_lo, -1.0f));
+}
+
+} // namespace math
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_TYPES_HAS_FLOAT16
+
+#endif // LLVM_LIBC_SRC___SUPPORT_MATH_EXP2M1F16_H

libc/src/math/generic/CMakeLists.txt

@@ -1488,19 +1488,7 @@ add_entrypoint_object(
   HDRS
     ../exp2m1f16.h
   DEPENDS
-    libc.hdr.errno_macros
-    libc.hdr.fenv_macros
-    libc.src.__support.common
-    libc.src.__support.FPUtil.cast
-    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.expxf16_utils
+    libc.src.__support.math.exp2m1f16
 )
 
 add_entrypoint_object(