sysdeps/ieee754/dbl-64/s_remquo.c

   1 /* Compute remainder and a congruent to the quotient.
   2    Copyright (C) 1997-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <math.h>
  20
  21 #include <math_private.h>
  22 #include <libm-alias-double.h>
  23 #include <stdint.h>
  24
  25 static const double zero = 0.0;
  26
  27
  28 double
  29 __remquo (double x, double y, int *quo)
  30 {
  31   int64_t hx, hy;
  32   uint64_t sx, qs;
  33   int cquo;
  34
  35   EXTRACT_WORDS64 (hx, x);
  36   EXTRACT_WORDS64 (hy, y);
  37   sx = hx & UINT64_C(0x8000000000000000);
  38   qs = sx ^ (hy & UINT64_C(0x8000000000000000));
  39   hy &= UINT64_C(0x7fffffffffffffff);
  40   hx &= UINT64_C(0x7fffffffffffffff);
  41
  42   /* Purge off exception values.  */
  43   if (__glibc_unlikely (hy == 0))
  44     return (x * y) / (x * y);                   /* y = 0 */
  45   if (__builtin_expect (hx >= UINT64_C(0x7ff0000000000000) /* x not finite */
  46                         || hy > UINT64_C(0x7ff0000000000000), 0))/* y is NaN */
  47     return (x * y) / (x * y);
  48
  49   if (hy <= UINT64_C(0x7fbfffffffffffff))
  50     x = __ieee754_fmod (x, 8 * y);              /* now x < 8y */
  51
  52   if (__glibc_unlikely (hx == hy))
  53     {
  54       *quo = qs ? -1 : 1;
  55       return zero * x;
  56     }
  57
  58   x = fabs (x);
  59   INSERT_WORDS64 (y, hy);
  60   cquo = 0;
  61
  62   if (hy <= UINT64_C(0x7fcfffffffffffff) && x >= 4 * y)
  63     {
  64       x -= 4 * y;
  65       cquo += 4;
  66     }
  67   if (hy <= UINT64_C(0x7fdfffffffffffff) && x >= 2 * y)
  68     {
  69       x -= 2 * y;
  70       cquo += 2;
  71     }
  72
  73   if (hy < UINT64_C(0x0020000000000000))
  74     {
  75       if (x + x > y)
  76         {
  77           x -= y;
  78           ++cquo;
  79           if (x + x >= y)
  80             {
  81               x -= y;
  82               ++cquo;
  83             }
  84         }
  85     }
  86   else
  87     {
  88       double y_half = 0.5 * y;
  89       if (x > y_half)
  90         {
  91           x -= y;
  92           ++cquo;
  93           if (x >= y_half)
  94             {
  95               x -= y;
  96               ++cquo;
  97             }
  98         }
  99     }
 100
 101   *quo = qs ? -cquo : cquo;
 102
 103   /* Ensure correct sign of zero result in round-downward mode.  */
 104   if (x == 0.0)
 105     x = 0.0;
 106   if (sx)
 107     x = -x;
 108   return x;
 109 }
 110 libm_alias_double (__remquo, remquo)