math/s_csqrt_template.c

   1 /* Complex square root of a float type.
   2    Copyright (C) 1997-2019 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Based on an algorithm by Stephen L. Moshier <moshier@world.std.com>.
   5    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
   6
   7    The GNU C Library is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU Lesser General Public
   9    License as published by the Free Software Foundation; either
  10    version 2.1 of the License, or (at your option) any later version.
  11
  12    The GNU C Library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    Lesser General Public License for more details.
  16
  17    You should have received a copy of the GNU Lesser General Public
  18    License along with the GNU C Library; if not, see
  19    <https://www.gnu.org/licenses/>.  */
  20
  21 #include <complex.h>
  22 #include <math.h>
  23 #include <math_private.h>
  24 #include <math-underflow.h>
  25 #include <float.h>
  26
  27 CFLOAT
  28 M_DECL_FUNC (__csqrt) (CFLOAT x)
  29 {
  30   CFLOAT res;
  31   int rcls = fpclassify (__real__ x);
  32   int icls = fpclassify (__imag__ x);
  33
  34   if (__glibc_unlikely (rcls <= FP_INFINITE || icls <= FP_INFINITE))
  35     {
  36       if (icls == FP_INFINITE)
  37         {
  38           __real__ res = M_HUGE_VAL;
  39           __imag__ res = __imag__ x;
  40         }
  41       else if (rcls == FP_INFINITE)
  42         {
  43           if (__real__ x < 0)
  44             {
  45               __real__ res = icls == FP_NAN ? M_NAN : 0;
  46               __imag__ res = M_COPYSIGN (M_HUGE_VAL, __imag__ x);
  47             }
  48           else
  49             {
  50               __real__ res = __real__ x;
  51               __imag__ res = (icls == FP_NAN
  52                               ? M_NAN : M_COPYSIGN (0, __imag__ x));
  53             }
  54         }
  55       else
  56         {
  57           __real__ res = M_NAN;
  58           __imag__ res = M_NAN;
  59         }
  60     }
  61   else
  62     {
  63       if (__glibc_unlikely (icls == FP_ZERO))
  64         {
  65           if (__real__ x < 0)
  66             {
  67               __real__ res = 0;
  68               __imag__ res = M_COPYSIGN (M_SQRT (-__real__ x), __imag__ x);
  69             }
  70           else
  71             {
  72               __real__ res = M_FABS (M_SQRT (__real__ x));
  73               __imag__ res = M_COPYSIGN (0, __imag__ x);
  74             }
  75         }
  76       else if (__glibc_unlikely (rcls == FP_ZERO))
  77         {
  78           FLOAT r;
  79           if (M_FABS (__imag__ x) >= 2 * M_MIN)
  80             r = M_SQRT (M_LIT (0.5) * M_FABS (__imag__ x));
  81           else
  82             r = M_LIT (0.5) * M_SQRT (2 * M_FABS (__imag__ x));
  83
  84           __real__ res = r;
  85           __imag__ res = M_COPYSIGN (r, __imag__ x);
  86         }
  87       else
  88         {
  89           FLOAT d, r, s;
  90           int scale = 0;
  91
  92           if (M_FABS (__real__ x) > M_MAX / 4)
  93             {
  94               scale = 1;
  95               __real__ x = M_SCALBN (__real__ x, -2 * scale);
  96               __imag__ x = M_SCALBN (__imag__ x, -2 * scale);
  97             }
  98           else if (M_FABS (__imag__ x) > M_MAX / 4)
  99             {
 100               scale = 1;
 101               if (M_FABS (__real__ x) >= 4 * M_MIN)
 102                 __real__ x = M_SCALBN (__real__ x, -2 * scale);
 103               else
 104                 __real__ x = 0;
 105               __imag__ x = M_SCALBN (__imag__ x, -2 * scale);
 106             }
 107           else if (M_FABS (__real__ x) < 2 * M_MIN
 108                    && M_FABS (__imag__ x) < 2 * M_MIN)
 109             {
 110               scale = -((M_MANT_DIG + 1) / 2);
 111               __real__ x = M_SCALBN (__real__ x, -2 * scale);
 112               __imag__ x = M_SCALBN (__imag__ x, -2 * scale);
 113             }
 114
 115           d = M_HYPOT (__real__ x, __imag__ x);
 116           /* Use the identity   2  Re res  Im res = Im x
 117              to avoid cancellation error in  d +/- Re x.  */
 118           if (__real__ x > 0)
 119             {
 120               r = M_SQRT (M_LIT (0.5) * (d + __real__ x));
 121               if (scale == 1 && M_FABS (__imag__ x) < 1)
 122                 {
 123                   /* Avoid possible intermediate underflow.  */
 124                   s = __imag__ x / r;
 125                   r = M_SCALBN (r, scale);
 126                   scale = 0;
 127                 }
 128               else
 129                 s = M_LIT (0.5) * (__imag__ x / r);
 130             }
 131           else
 132             {
 133               s = M_SQRT (M_LIT (0.5) * (d - __real__ x));
 134               if (scale == 1 && M_FABS (__imag__ x) < 1)
 135                 {
 136                   /* Avoid possible intermediate underflow.  */
 137                   r = M_FABS (__imag__ x / s);
 138                   s = M_SCALBN (s, scale);
 139                   scale = 0;
 140                 }
 141               else
 142                 r = M_FABS (M_LIT (0.5) * (__imag__ x / s));
 143             }
 144
 145           if (scale)
 146             {
 147               r = M_SCALBN (r, scale);
 148               s = M_SCALBN (s, scale);
 149             }
 150
 151           math_check_force_underflow (r);
 152           math_check_force_underflow (s);
 153
 154           __real__ res = r;
 155           __imag__ res = M_COPYSIGN (s, __imag__ x);
 156         }
 157     }
 158
 159   return res;
 160 }
 161 declare_mgen_alias (__csqrt, csqrt)