libgcc/config/rs6000/_divkc3.c

   1 /* Copyright (C) 1989-2024 Free Software Foundation, Inc.
   2
   3 This file is part of GCC.
   4
   5 GCC is free software; you can redistribute it and/or modify it under
   6 the terms of the GNU General Public License as published by the Free
   7 Software Foundation; either version 3, or (at your option) any later
   8 version.
   9
  10 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
  11 WARRANTY; without even the implied warranty of MERCHANTABILITY or
  12 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  13 for more details.
  14
  15 Under Section 7 of GPL version 3, you are granted additional
  16 permissions described in the GCC Runtime Library Exception, version
  17 3.1, as published by the Free Software Foundation.
  18
  19 You should have received a copy of the GNU General Public License and
  20 a copy of the GCC Runtime Library Exception along with this program;
  21 see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  22 <http://www.gnu.org/licenses/>.  */
  23
  24 /* This is a temporary specialization of code from libgcc/libgcc2.c.  */
  25
  26 #include "soft-fp.h"
  27 #include "quad-float128.h"
  28
  29 /* Use the correct built-in function based on whether TFmode is _Float128 or
  30    long double.  See quad-float128.h for more details.  */
  31 #ifndef __LONG_DOUBLE_IEEE128__
  32 #define COPYSIGN(x,y) __builtin_copysignf128 (x, y)
  33 #define INFINITY __builtin_inff128 ()
  34 #define FABS __builtin_fabsf128
  35
  36 #else
  37 #define COPYSIGN(x,y) __builtin_copysignl (x, y)
  38 #define INFINITY __builtin_infl ()
  39 #define FABS __builtin_fabsl
  40 #endif
  41
  42 #define isnan __builtin_isnan
  43 #define isinf __builtin_isinf
  44 #define isfinite __builtin_isfinite
  45
  46 #if defined(FLOAT128_HW_INSNS) && !defined(__divkc3)
  47 #define __divkc3 __divkc3_sw
  48 #endif
  49
  50 #ifndef __LONG_DOUBLE_IEEE128__
  51 #define RBIG   (__LIBGCC_KF_MAX__ / 2)
  52 #define RMIN   (__LIBGCC_KF_MIN__)
  53 #define RMIN2  (__LIBGCC_KF_EPSILON__)
  54 #define RMINSCAL (1 / __LIBGCC_KF_EPSILON__)
  55 #define RMAX2  (RBIG * RMIN2)
  56 #else
  57 #define RBIG   (__LIBGCC_TF_MAX__ / 2)
  58 #define RMIN   (__LIBGCC_TF_MIN__)
  59 #define RMIN2  (__LIBGCC_TF_EPSILON__)
  60 #define RMINSCAL (1 / __LIBGCC_TF_EPSILON__)
  61 #define RMAX2  (RBIG * RMIN2)
  62 #endif
  63
  64 TCtype
  65 __divkc3 (TFtype a, TFtype b, TFtype c, TFtype d)
  66 {
  67   TFtype denom, ratio, x, y;
  68   TCtype res;
  69
  70   /* long double has significant potential underflow/overflow errors that
  71      can be greatly reduced with a limited number of tests and adjustments.
  72   */
  73
  74   /* Scale by max(c,d) to reduce chances of denominator overflowing.  */
  75   if (FABS (c) < FABS (d))
  76     {
  77       /* Prevent underflow when denominator is near max representable.  */
  78       if (FABS (d) >= RBIG)
  79         {
  80           a = a / 2;
  81           b = b / 2;
  82           c = c / 2;
  83           d = d / 2;
  84         }
  85       /* Avoid overflow/underflow issues when c and d are small.
  86          Scaling up helps avoid some underflows.
  87          No new overflow possible since c&d < RMIN2.  */
  88       if (FABS (d) < RMIN2)
  89         {
  90           a = a * RMINSCAL;
  91           b = b * RMINSCAL;
  92           c = c * RMINSCAL;
  93           d = d * RMINSCAL;
  94         }
  95       else
  96         {
  97           if (((FABS (a) < RMIN) && (FABS (b) < RMAX2) && (FABS (d) < RMAX2))
  98               || ((FABS (b) < RMIN) && (FABS (a) < RMAX2)
  99                   && (FABS (d) < RMAX2)))
 100             {
 101               a = a * RMINSCAL;
 102               b = b * RMINSCAL;
 103               c = c * RMINSCAL;
 104               d = d * RMINSCAL;
 105             }
 106         }
 107       ratio = c / d;
 108       denom = (c * ratio) + d;
 109       /* Choose alternate order of computation if ratio is subnormal.  */
 110       if (FABS (ratio) > RMIN)
 111         {
 112           x = ((a * ratio) + b) / denom;
 113           y = ((b * ratio) - a) / denom;
 114         }
 115       else
 116         {
 117           x = ((c * (a / d)) + b) / denom;
 118           y = ((c * (b / d)) - a) / denom;
 119         }
 120     }
 121   else
 122     {
 123       /* Prevent underflow when denominator is near max representable.  */
 124       if (FABS (c) >= RBIG)
 125         {
 126           a = a / 2;
 127           b = b / 2;
 128           c = c / 2;
 129           d = d / 2;
 130         }
 131       /* Avoid overflow/underflow issues when both c and d are small.
 132          Scaling up helps avoid some underflows.
 133          No new overflow possible since both c&d are less than RMIN2.  */
 134       if (FABS (c) < RMIN2)
 135         {
 136           a = a * RMINSCAL;
 137           b = b * RMINSCAL;
 138           c = c * RMINSCAL;
 139           d = d * RMINSCAL;
 140         }
 141       else
 142         {
 143           if (((FABS (a) < RMIN) && (FABS (b) < RMAX2) && (FABS (c) < RMAX2))
 144               || ((FABS (b) < RMIN) && (FABS (a) < RMAX2)
 145                   && (FABS (c) < RMAX2)))
 146             {
 147               a = a * RMINSCAL;
 148               b = b * RMINSCAL;
 149               c = c * RMINSCAL;
 150               d = d * RMINSCAL;
 151             }
 152         }
 153       ratio = d / c;
 154       denom = (d * ratio) + c;
 155       /* Choose alternate order of computation if ratio is subnormal.  */
 156       if (FABS (ratio) > RMIN)
 157         {
 158           x = ((b * ratio) + a) / denom;
 159           y = (b - (a * ratio)) / denom;
 160         }
 161       else
 162         {
 163           x = (a + (d * (b / c))) / denom;
 164           y = (b - (d * (a / c))) / denom;
 165         }
 166     }
 167
 168   /* Recover infinities and zeros that computed as NaN+iNaN; the only cases
 169      are nonzero/zero, infinite/finite, and finite/infinite.  */
 170   if (isnan (x) && isnan (y))
 171     {
 172       if (c == 0.0 && d == 0.0 && (!isnan (a) || !isnan (b)))
 173         {
 174           x = COPYSIGN (INFINITY, c) * a;
 175           y = COPYSIGN (INFINITY, c) * b;
 176         }
 177       else if ((isinf (a) || isinf (b)) && isfinite (c) && isfinite (d))
 178         {
 179           a = COPYSIGN (isinf (a) ? 1 : 0, a);
 180           b = COPYSIGN (isinf (b) ? 1 : 0, b);
 181           x = INFINITY * (a * c + b * d);
 182           y = INFINITY * (b * c - a * d);
 183         }
 184       else if ((isinf (c) || isinf (d)) && isfinite (a) && isfinite (b))
 185         {
 186           c = COPYSIGN (isinf (c) ? 1 : 0, c);
 187           d = COPYSIGN (isinf (d) ? 1 : 0, d);
 188           x = 0.0 * (a * c + b * d);
 189           y = 0.0 * (b * c - a * d);
 190         }
 191     }
 192
 193   __real__ res = x;
 194   __imag__ res = y;
 195   return res;
 196 }