libc/src/math/generic/acoshf.cpp

   1 //===-- Single-precision acosh function -----------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "src/math/acoshf.h"
  10 #include "src/__support/FPUtil/FEnvImpl.h"
  11 #include "src/__support/FPUtil/FPBits.h"
  12 #include "src/__support/FPUtil/PolyEval.h"
  13 #include "src/__support/FPUtil/multiply_add.h"
  14 #include "src/__support/FPUtil/sqrt.h"
  15 #include "src/__support/macros/config.h"
  16 #include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
  17 #include "src/math/generic/common_constants.h"
  18 #include "src/math/generic/explogxf.h"
  19
  20 namespace LIBC_NAMESPACE_DECL {
  21
  22 LLVM_LIBC_FUNCTION(float, acoshf, (float x)) {
  23   using FPBits_t = typename fputil::FPBits<float>;
  24   FPBits_t xbits(x);
  25   uint32_t x_u = xbits.uintval();
  26
  27   if (LIBC_UNLIKELY(x <= 1.0f)) {
  28     if (x == 1.0f)
  29       return 0.0f;
  30     // x < 1.
  31     fputil::set_errno_if_required(EDOM);
  32     fputil::raise_except_if_required(FE_INVALID);
  33     return FPBits_t::quiet_nan().get_val();
  34   }
  35
  36   if (LIBC_UNLIKELY(x_u >= 0x4f8ffb03)) {
  37     if (LIBC_UNLIKELY(xbits.is_inf_or_nan()))
  38       return x;
  39
  40     // Helper functions to set results for exceptional cases.
  41     auto round_result_slightly_down = [](float r) -> float {
  42       volatile float tmp = r;
  43       tmp = tmp - 0x1.0p-25f;
  44       return tmp;
  45     };
  46     auto round_result_slightly_up = [](float r) -> float {
  47       volatile float tmp = r;
  48       tmp = tmp + 0x1.0p-25f;
  49       return tmp;
  50     };
  51
  52     switch (x_u) {
  53     case 0x4f8ffb03: // x = 0x1.1ff606p32f
  54       return round_result_slightly_up(0x1.6fdd34p4f);
  55     case 0x5c569e88: // x = 0x1.ad3d1p57f
  56       return round_result_slightly_up(0x1.45c146p5f);
  57     case 0x5e68984e: // x = 0x1.d1309cp61f
  58       return round_result_slightly_up(0x1.5c9442p5f);
  59     case 0x655890d3: // x = 0x1.b121a6p75f
  60       return round_result_slightly_down(0x1.a9a3f2p5f);
  61     case 0x6eb1a8ec: // x = 0x1.6351d8p94f
  62       return round_result_slightly_down(0x1.08b512p6f);
  63     case 0x7997f30a: // x = 0x1.2fe614p116f
  64       return round_result_slightly_up(0x1.451436p6f);
  65     }
  66   }
  67
  68   double x_d = static_cast<double>(x);
  69   // acosh(x) = log(x + sqrt(x^2 - 1))
  70   return static_cast<float>(log_eval(
  71       x_d + fputil::sqrt<double>(fputil::multiply_add(x_d, x_d, -1.0))));
  72 }
  73
  74 } // namespace LIBC_NAMESPACE_DECL