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/optimization.h" // LIBC_UNLIKELY
  16 #include "src/math/generic/common_constants.h"
  17 #include "src/math/generic/explogxf.h"
  18
  19 namespace LIBC_NAMESPACE {
  20
  21 LLVM_LIBC_FUNCTION(float, acoshf, (float x)) {
  22   using FPBits_t = typename fputil::FPBits<float>;
  23   FPBits_t xbits(x);
  24   uint32_t x_u = xbits.uintval();
  25
  26   if (LIBC_UNLIKELY(x <= 1.0f)) {
  27     if (x == 1.0f)
  28       return 0.0f;
  29     // x < 1.
  30     fputil::set_errno_if_required(EDOM);
  31     fputil::raise_except_if_required(FE_INVALID);
  32     return FPBits_t::build_quiet_nan(0);
  33   }
  34
  35   if (LIBC_UNLIKELY(x_u >= 0x4f8ffb03)) {
  36     // Check for exceptional values.
  37     uint32_t x_abs = x_u & FPBits_t::FloatProp::EXP_MANT_MASK;
  38     if (LIBC_UNLIKELY(x_abs >= 0x7f80'0000U)) {
  39       // x is +inf or NaN.
  40       return x;
  41     }
  42
  43     // Helper functions to set results for exceptional cases.
  44     auto round_result_slightly_down = [](float r) -> float {
  45       volatile float tmp = r;
  46       tmp = tmp - 0x1.0p-25f;
  47       return tmp;
  48     };
  49     auto round_result_slightly_up = [](float r) -> float {
  50       volatile float tmp = r;
  51       tmp = tmp + 0x1.0p-25f;
  52       return tmp;
  53     };
  54
  55     switch (x_u) {
  56     case 0x4f8ffb03: // x = 0x1.1ff606p32f
  57       return round_result_slightly_up(0x1.6fdd34p4f);
  58     case 0x5c569e88: // x = 0x1.ad3d1p57f
  59       return round_result_slightly_up(0x1.45c146p5f);
  60     case 0x5e68984e: // x = 0x1.d1309cp61f
  61       return round_result_slightly_up(0x1.5c9442p5f);
  62     case 0x655890d3: // x = 0x1.b121a6p75f
  63       return round_result_slightly_down(0x1.a9a3f2p5f);
  64     case 0x6eb1a8ec: // x = 0x1.6351d8p94f
  65       return round_result_slightly_down(0x1.08b512p6f);
  66     case 0x7997f30a: // x = 0x1.2fe614p116f
  67       return round_result_slightly_up(0x1.451436p6f);
  68     }
  69   }
  70
  71   double x_d = static_cast<double>(x);
  72   // acosh(x) = log(x + sqrt(x^2 - 1))
  73   return static_cast<float>(
  74       log_eval(x_d + fputil::sqrt(fputil::multiply_add(x_d, x_d, -1.0))));
  75 }
  76
  77 } // namespace LIBC_NAMESPACE