[libc][math] Refactor exp10f16 implementation to header-only in src/__support/math folder.

libc/shared/math.h

@@ -14,6 +14,7 @@
 #include "math/exp.h"
 #include "math/exp10.h"
 #include "math/exp10f.h"
+#include "math/exp10f16.h"
 #include "math/expf.h"
 #include "math/expf16.h"
 #include "math/frexpf.h"

libc/shared/math/exp10f16.h

@@ -0,0 +1,29 @@
+//===-- Shared exp10f16 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_EXP10F_H
+#define LLVM_LIBC_SHARED_MATH_EXP10F_H
+
+#include "include/llvm-libc-macros/float16-macros.h"
+
+#ifdef LIBC_TYPES_HAS_FLOAT16
+
+#include "shared/libc_common.h"
+#include "src/__support/math/exp10f16.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace shared {
+
+using math::exp10f16;
+
+} // namespace shared
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_TYPES_HAS_FLOAT16
+
+#endif // LLVM_LIBC_SHARED_MATH_EXP10F_H

libc/src/__support/math/CMakeLists.txt

@@ -198,3 +198,37 @@ add_header_library(
     libc.src.__support.FPUtil.rounding_mode
     libc.src.__support.macros.optimization
 )
+
+add_header_library(
+  exp10_float16_constants
+  HDRS
+    exp10_float16_constants.h
+  DEPENDS
+    libc.src.__support.CPP.array
+)
+
+add_header_library(
+  exp10f16_utils
+  HDRS
+    exp10f16_utils.h
+  DEPENDS
+    .expf16_utils
+    .exp10_float16_constants
+    libc.src.__support.FPUtil.fp_bits
+)
+
+add_header_library(
+  exp10f16
+  HDRS
+    exp10f16.h
+  DEPENDS
+    .exp10f16_utils
+    libc.src.__support.FPUtil.fp_bits
+    src.__support.FPUtil.FEnvImpl
+    src.__support.FPUtil.FPBits
+    src.__support.FPUtil.cast
+    src.__support.FPUtil.rounding_mode
+    src.__support.FPUtil.except_value_utils
+    src.__support.macros.optimization
+    src.__support.macros.properties.cpu_features
+)

libc/src/__support/math/exp10_float16_constants.h

@@ -0,0 +1,43 @@
+//===-- Constants for exp10f16 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_SRC___SUPPORT_MATH_EXP10_FLOAT16_CONSTANTS_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_EXP10_FLOAT16_CONSTANTS_H
+
+#include "include/llvm-libc-macros/float16-macros.h"
+#include <stdint.h>
+
+#ifdef LIBC_TYPES_HAS_FLOAT16
+
+#include "src/__support/CPP/array.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+// Generated by Sollya with the following commands:
+//   > display = hexadecimal;
+//   > for i from 0 to 7 do printsingle(round(2^(i * 2^-3), SG, RN));
+static constexpr cpp::array<uint32_t, 8> EXP2_MID_BITS = {
+    0x3f80'0000U, 0x3f8b'95c2U, 0x3f98'37f0U, 0x3fa5'fed7U,
+    0x3fb5'04f3U, 0x3fc5'672aU, 0x3fd7'44fdU, 0x3fea'c0c7U,
+};
+
+// Generated by Sollya with the following commands:
+//   > display = hexadecimal;
+//   > round(log2(10), SG, RN);
+static constexpr float LOG2F_10 = 0x1.a934fp+1f;
+
+// Generated by Sollya with the following commands:
+//   > display = hexadecimal;
+//   > round(log10(2), SG, RN);
+static constexpr float LOG10F_2 = 0x1.344136p-2f;
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_TYPES_HAS_FLOAT16
+
+#endif // LLVM_LIBC_SRC___SUPPORT_MATH_EXP10F16_H

libc/src/__support/math/exp10f16.h

@@ -0,0 +1,141 @@
+//===-- Implementation header for exp10f16 ----------------------*- 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_EXP10F16_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_EXP10F16_H
+
+#include "include/llvm-libc-macros/float16-macros.h"
+
+#ifdef LIBC_TYPES_HAS_FLOAT16
+
+#include "exp10f16_utils.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/cast.h"
+#include "src/__support/FPUtil/except_value_utils.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"
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+#ifdef LIBC_TARGET_CPU_HAS_FMA_FLOAT
+static constexpr size_t N_EXP10F16_EXCEPTS = 5;
+#else
+static constexpr size_t N_EXP10F16_EXCEPTS = 8;
+#endif
+
+static constexpr fputil::ExceptValues<float16, N_EXP10F16_EXCEPTS>
+    EXP10F16_EXCEPTS = {{
+        // x = 0x1.8f4p-2, exp10f16(x) = 0x1.3ap+1 (RZ)
+        {0x363dU, 0x40e8U, 1U, 0U, 1U},
+        // x = 0x1.95cp-2, exp10f16(x) = 0x1.3ecp+1 (RZ)
+        {0x3657U, 0x40fbU, 1U, 0U, 0U},
+        // x = -0x1.018p-4, exp10f16(x) = 0x1.bbp-1 (RZ)
+        {0xac06U, 0x3aecU, 1U, 0U, 0U},
+        // x = -0x1.c28p+0, exp10f16(x) = 0x1.1ccp-6 (RZ)
+        {0xbf0aU, 0x2473U, 1U, 0U, 0U},
+        // x = -0x1.e1cp+1, exp10f16(x) = 0x1.694p-13 (RZ)
+        {0xc387U, 0x09a5U, 1U, 0U, 0U},
+#ifndef LIBC_TARGET_CPU_HAS_FMA_FLOAT
+        // x = 0x1.0cp+1, exp10f16(x) = 0x1.f04p+6 (RZ)
+        {0x4030U, 0x57c1U, 1U, 0U, 1U},
+        // x = 0x1.1b8p+1, exp10f16(x) = 0x1.47cp+7 (RZ)
+        {0x406eU, 0x591fU, 1U, 0U, 1U},
+        // x = 0x1.1b8p+2, exp10f16(x) = 0x1.a4p+14 (RZ)
+        {0x446eU, 0x7690U, 1U, 0U, 1U},
+#endif
+    }};
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+static constexpr float16 exp10f16(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| >= 5, or x is NaN.
+  if (LIBC_UNLIKELY(x_abs >= 0x4500U)) {
+    // exp10(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 >= 5.
+    if (x_bits.is_pos()) {
+      // exp10(+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 <= -8.
+    if (x_u >= 0xc800U) {
+      // exp10(-inf) = +0
+      if (x_bits.is_inf())
+        return FPBits::zero().get_val();
+
+      fputil::set_errno_if_required(ERANGE);
+      fputil::raise_except_if_required(FE_UNDERFLOW | FE_INEXACT);
+
+      if (fputil::fenv_is_round_up())
+        return FPBits::min_subnormal().get_val();
+      return FPBits::zero().get_val();
+    }
+  }
+
+  // When x is 1, 2, 3, or 4. These are hard-to-round cases with exact results.
+  if (LIBC_UNLIKELY((x_u & ~(0x3c00U | 0x4000U | 0x4200U | 0x4400U)) == 0)) {
+    switch (x_u) {
+    case 0x3c00U: // x = 1.0f16
+      return fputil::cast<float16>(10.0);
+    case 0x4000U: // x = 2.0f16
+      return fputil::cast<float16>(100.0);
+    case 0x4200U: // x = 3.0f16
+      return fputil::cast<float16>(1'000.0);
+    case 0x4400U: // x = 4.0f16
+      return fputil::cast<float16>(10'000.0);
+    }
+  }
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+  if (auto r = EXP10F16_EXCEPTS.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
+    return r.value();
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+  // 10^x = 2^((hi + mid) * log2(10)) * 10^lo
+  auto [exp2_hi_mid, exp10_lo] = exp10_range_reduction(x);
+  return fputil::cast<float16>(exp2_hi_mid * exp10_lo);
+}
+
+} // namespace math
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_TYPES_HAS_FLOAT16
+
+#endif // LLVM_LIBC_SRC___SUPPORT_MATH_EXP10F16_H

libc/src/__support/math/exp10f16_utils.h

@@ -0,0 +1,64 @@
+//===-- Common utils for exp10f16 -------------------------------*- 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_EXP_FLOAT_CONSTANTS_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_EXP_FLOAT_CONSTANTS_H
+
+#include "include/llvm-libc-macros/float16-macros.h"
+
+#ifdef LIBC_TYPES_HAS_FLOAT16
+
+#include "exp10_float16_constants.h"
+#include "expf16_utils.h"
+#include "src/__support/FPUtil/FPBits.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+LIBC_INLINE static constexpr ExpRangeReduction
+exp10_range_reduction(float16 x) {
+  // For -8 < x < 5, to compute 10^x, we perform the following range reduction:
+  // find hi, mid, lo, such that:
+  //   x = (hi + mid) * log2(10) + 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,
+  //   10^x = 10^(hi + mid + lo) = 2^((hi + mid) * log2(10)) + 10^lo
+  // We store 2^mid in the lookup table EXP2_MID_BITS, and compute 2^hi * 2^mid
+  // by adding hi to the exponent field of 2^mid.  10^lo is computed using a
+  // degree-4 minimax polynomial generated by Sollya.
+
+  float xf = x;
+  float kf = fputil::nearest_integer(xf * (LOG2F_10 * 0x1.0p+3f));
+  int x_hi_mid = static_cast<int>(kf);
+  unsigned x_hi = static_cast<unsigned>(x_hi_mid) >> 3;
+  unsigned x_mid = static_cast<unsigned>(x_hi_mid) & 0x7;
+  // lo = x - (hi + mid) = round(x * 2^3 * log2(10)) * log10(2) * (-2^(-3)) + x
+  float lo = fputil::multiply_add(kf, LOG10F_2 * -0x1.0p-3f, xf);
+
+  uint32_t exp2_hi_mid_bits =
+      EXP2_MID_BITS[x_mid] +
+      static_cast<uint32_t>(x_hi << fputil::FPBits<float>::FRACTION_LEN);
+  float exp2_hi_mid = fputil::FPBits<float>(exp2_hi_mid_bits).get_val();
+  // Degree-4 minimax polynomial generated by Sollya with the following
+  // commands:
+  //   > display = hexadecimal;
+  //   > P = fpminimax((10^x - 1)/x, 3, [|SG...|], [-2^-4, 2^-4]);
+  //   > 1 + x * P;
+  float exp10_lo = fputil::polyeval(lo, 0x1p+0f, 0x1.26bb14p+1f, 0x1.53526p+1f,
+                                    0x1.04b434p+1f, 0x1.2bcf9ep+0f);
+  return {exp2_hi_mid, exp10_lo};
+}
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_TYPES_HAS_FLOAT16
+
+#endif // LLVM_LIBC_SRC___SUPPORT_MATH_EXP10F16_H

libc/src/math/generic/CMakeLists.txt

@@ -1477,20 +1477,8 @@ add_entrypoint_object(
   HDRS
     ../exp10f16.h
   DEPENDS
-    .expxf16
-    libc.hdr.errno_macros
-    libc.hdr.fenv_macros
-    libc.src.__support.CPP.array
-    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.nearest_integer
-    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.exp10f16
+    libc.src.errno.errno
 )
 
 add_entrypoint_object(
@@ -1519,7 +1507,6 @@ add_entrypoint_object(
   HDRS
     ../exp10m1f16.h
   DEPENDS
-    .expxf16
     libc.hdr.errno_macros
     libc.hdr.fenv_macros
     libc.src.__support.FPUtil.cast
@@ -1531,6 +1518,7 @@ add_entrypoint_object(
     libc.src.__support.FPUtil.rounding_mode
     libc.src.__support.macros.optimization
     libc.src.__support.macros.properties.cpu_features
+    libc.src.__support.math.exp10f16_utils
 )
 
 add_entrypoint_object(
@@ -5023,10 +5011,11 @@ add_header_library(
   HDRS
     expxf16.h
   DEPENDS
-    libc.src.__support.FPUtil.cast
     libc.src.__support.FPUtil.fp_bits
+    libc.src.__support.FPUtil.cast
     libc.src.__support.FPUtil.multiply_add
     libc.src.__support.FPUtil.nearest_integer
     libc.src.__support.macros.attributes
     libc.src.__support.math.expf16_utils
+    libc.src.__support.math.exp10_float16_constants
 )