[libc][math][c23] Add exp10f16 C23 math function

libc/config/linux/x86_64/entrypoints.txt

@@ -576,6 +576,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
     libc.src.math.canonicalizef16
     libc.src.math.ceilf16
     libc.src.math.copysignf16
+    libc.src.math.exp10f16
     libc.src.math.exp2f16
     libc.src.math.expf16
     libc.src.math.f16add

libc/docs/math/index.rst

@@ -286,7 +286,7 @@ Higher Math Functions
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
 | exp       | |check|          | |check|         |                        | |check|              |                        | 7.12.6.1               | F.10.3.1                   |
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
-| exp10     | |check|          | |check|         |                        |                      |                        | 7.12.6.2               | F.10.3.2                   |
+| exp10     | |check|          | |check|         |                        | |check|              |                        | 7.12.6.2               | F.10.3.2                   |
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
 | exp10m1   |                  |                 |                        |                      |                        | 7.12.6.3               | F.10.3.3                   |
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+

libc/spec/stdc.td

@@ -591,6 +591,7 @@ def StdC : StandardSpec<"stdc"> {
 
           FunctionSpec<"exp10", RetValSpec<DoubleType>, [ArgSpec<DoubleType>]>,
           FunctionSpec<"exp10f", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
+          GuardedFunctionSpec<"exp10f16", RetValSpec<Float16Type>, [ArgSpec<Float16Type>], "LIBC_TYPES_HAS_FLOAT16">,
 
           FunctionSpec<"remainder", RetValSpec<DoubleType>, [ArgSpec<DoubleType>, ArgSpec<DoubleType>]>,
           FunctionSpec<"remainderf", RetValSpec<FloatType>, [ArgSpec<FloatType>, ArgSpec<FloatType>]>,

libc/src/math/CMakeLists.txt

@@ -116,6 +116,7 @@ add_math_entrypoint_object(exp2m1f)
 
 add_math_entrypoint_object(exp10)
 add_math_entrypoint_object(exp10f)
+add_math_entrypoint_object(exp10f16)
 
 add_math_entrypoint_object(expm1)
 add_math_entrypoint_object(expm1f)

libc/src/math/exp10f16.h

@@ -0,0 +1,21 @@
+//===-- 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_MATH_EXP10F16_H
+#define LLVM_LIBC_SRC_MATH_EXP10F16_H
+
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/properties/types.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+float16 exp10f16(float16 x);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_MATH_EXP10F16_H

libc/src/math/generic/CMakeLists.txt

@@ -1402,6 +1402,7 @@ add_entrypoint_object(
   HDRS
     ../exp2f16.h
   DEPENDS
+    .expxf16
     libc.hdr.errno_macros
     libc.hdr.fenv_macros
     libc.src.__support.CPP.array
@@ -1497,6 +1498,30 @@ add_entrypoint_object(
     -O3
 )
 
+add_entrypoint_object(
+  exp10f16
+  SRCS
+    exp10f16.cpp
+  HDRS
+    ../exp10f16.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
+    libc.src.__support.macros.properties.cpu_features
+  COMPILE_OPTIONS
+    -O3
+)
+
 add_entrypoint_object(
   expm1
   SRCS
@@ -4760,3 +4785,11 @@ add_entrypoint_object(
   COMPILE_OPTIONS
     -O3
 )
+
+add_header_library(
+  expxf16
+  HDRS
+    expxf16.h
+  DEPENDS
+    libc.src.__support.CPP.array
+)

libc/src/math/generic/exp10f16.cpp

@@ -0,0 +1,170 @@
+//===-- Half-precision 10^x 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/exp10f16.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"
+#include "src/__support/macros/optimization.h"
+#include "src/__support/macros/properties/cpu_features.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+#ifdef LIBC_TARGET_CPU_HAS_FMA
+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
+        // 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
+    }};
+
+// 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;
+
+LLVM_LIBC_FUNCTION(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 static_cast<float16>(10.0);
+    case 0x4000U: // x = 2.0f16
+      return static_cast<float16>(100.0);
+    case 0x4200U: // x = 3.0f16
+      return static_cast<float16>(1'000.0);
+    case 0x4400U: // x = 4.0f16
+      return static_cast<float16>(10'000.0);
+    }
+  }
+
+  if (auto r = EXP10F16_EXCEPTS.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
+    return r.value();
+
+  // 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);
+  int x_hi = x_hi_mid >> 3;
+  int x_mid = 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 static_cast<float16>(exp2_hi_mid * exp10_lo);
+}
+
+} // namespace LIBC_NAMESPACE_DECL

libc/src/math/generic/exp2f16.cpp

@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "src/math/exp2f16.h"
+#include "expxf16.h"
 #include "hdr/errno_macros.h"
 #include "hdr/fenv_macros.h"
 #include "src/__support/CPP/array.h"
@@ -33,14 +34,6 @@ static constexpr fputil::ExceptValues<float16, 3> EXP2F16_EXCEPTS = {{
     {0xaf57U, 0x3b63U, 1U, 0U, 0U},
 }};
 
-// 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,
-};
-
 LLVM_LIBC_FUNCTION(float16, exp2f16, (float16 x)) {
   using FPBits = fputil::FPBits<float16>;
   FPBits x_bits(x);

libc/src/math/generic/expxf16.h

@@ -0,0 +1,28 @@
+//===-- Common utilities for half-precision exponential functions ---------===//
+//
+// 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_GENERIC_EXPXF16_H
+#define LLVM_LIBC_SRC_MATH_GENERIC_EXPXF16_H
+
+#include "src/__support/CPP/array.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 0 to 7 do printsingle(round(2^(i * 2^-3), SG, RN));
+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,
+};
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_MATH_GENERIC_EXPXF16_H

libc/test/src/math/CMakeLists.txt

@@ -990,6 +990,19 @@ add_fp_unittest(
     libc.src.__support.FPUtil.fp_bits
 )
 
+add_fp_unittest(
+  exp10_test
+  NEED_MPFR
+  SUITE
+    libc-math-unittests
+  SRCS
+    exp10_test.cpp
+  DEPENDS
+    libc.src.errno.errno
+    libc.src.math.exp10
+    libc.src.__support.FPUtil.fp_bits
+)
+
 add_fp_unittest(
   exp10f_test
   NEED_MPFR
@@ -1004,16 +1017,14 @@ add_fp_unittest(
 )
 
 add_fp_unittest(
- exp10_test
- NEED_MPFR
- SUITE
-   libc-math-unittests
- SRCS
-   exp10_test.cpp
- DEPENDS
-   libc.src.errno.errno
-   libc.src.math.exp10
-   libc.src.__support.FPUtil.fp_bits
+  exp10f16_test
+  NEED_MPFR
+  SUITE
+    libc-math-unittests
+  SRCS
+    exp10f16_test.cpp
+  DEPENDS
+    libc.src.math.exp10f16
 )
 
 add_fp_unittest(