libc/src/math/generic/atanhf.cpp

   1 //===-- Single-precision atanh 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/atanhf.h"
  10 #include "src/__support/FPUtil/FPBits.h"
  11 #include "src/__support/macros/config.h"
  12 #include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
  13 #include "src/math/generic/explogxf.h"
  14
  15 namespace LIBC_NAMESPACE_DECL {
  16
  17 LLVM_LIBC_FUNCTION(float, atanhf, (float x)) {
  18   using FPBits = typename fputil::FPBits<float>;
  19
  20   FPBits xbits(x);
  21   Sign sign = xbits.sign();
  22   uint32_t x_abs = xbits.abs().uintval();
  23
  24   // |x| >= 1.0
  25   if (LIBC_UNLIKELY(x_abs >= 0x3F80'0000U)) {
  26     if (xbits.is_nan()) {
  27       return x;
  28     }
  29     // |x| == 1.0
  30     if (x_abs == 0x3F80'0000U) {
  31       fputil::set_errno_if_required(ERANGE);
  32       fputil::raise_except_if_required(FE_DIVBYZERO);
  33       return FPBits::inf(sign).get_val();
  34     } else {
  35       fputil::set_errno_if_required(EDOM);
  36       fputil::raise_except_if_required(FE_INVALID);
  37       return FPBits::quiet_nan().get_val();
  38     }
  39   }
  40
  41   // |x| < ~0.10
  42   if (LIBC_UNLIKELY(x_abs <= 0x3dcc'0000U)) {
  43     // |x| <= 2^-26
  44     if (LIBC_UNLIKELY(x_abs <= 0x3280'0000U)) {
  45       return static_cast<float>(LIBC_UNLIKELY(x_abs == 0)
  46                                     ? x
  47                                     : (x + 0x1.5555555555555p-2 * x * x * x));
  48     }
  49
  50     double xdbl = x;
  51     double x2 = xdbl * xdbl;
  52     // Pure Taylor series.
  53     double pe = fputil::polyeval(x2, 0.0, 0x1.5555555555555p-2,
  54                                  0x1.999999999999ap-3, 0x1.2492492492492p-3,
  55                                  0x1.c71c71c71c71cp-4, 0x1.745d1745d1746p-4);
  56     return static_cast<float>(fputil::multiply_add(xdbl, pe, xdbl));
  57   }
  58   double xdbl = x;
  59   return static_cast<float>(0.5 * log_eval((xdbl + 1.0) / (xdbl - 1.0)));
  60 }
  61
  62 } // namespace LIBC_NAMESPACE_DECL