sysdeps/ieee754/dbl-64/s_floor.c

   1 /* Round double to integer away from zero.
   2    Copyright (C) 2011-2021 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 2011.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <https://www.gnu.org/licenses/>.  */
  19
  20 /* Based on a version which carries the following copyright:  */
  21
  22 /*
  23  * ====================================================
  24  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
  25  *
  26  * Developed at SunPro, a Sun Microsystems, Inc. business.
  27  * Permission to use, copy, modify, and distribute this
  28  * software is freely granted, provided that this notice
  29  * is preserved.
  30  * ====================================================
  31  */
  32
  33 #define NO_MATH_REDIRECT
  34 #include <math.h>
  35 #include <math_private.h>
  36 #include <stdint.h>
  37 #include <libm-alias-double.h>
  38 #include <math-use-builtins.h>
  39
  40 /*
  41  * floor(x)
  42  * Return x rounded toward -inf to integral value
  43  * Method:
  44  *      Bit twiddling.
  45  */
  46
  47
  48 double
  49 __floor (double x)
  50 {
  51 #if USE_FLOOR_BUILTIN
  52   return __builtin_floor (x);
  53 #else
  54   /* Use generic implementation.  */
  55   int64_t i0;
  56   EXTRACT_WORDS64 (i0, x);
  57   int32_t j0 = ((i0 >> 52) & 0x7ff) - 0x3ff;
  58   if (__glibc_likely (j0 < 52))
  59     {
  60       if (j0 < 0)
  61         {
  62           /* return 0 * sign (x) if |x| < 1  */
  63           if (i0 >= 0)
  64             i0 = 0;
  65           else if ((i0 & 0x7fffffffffffffffl) != 0)
  66             i0 = 0xbff0000000000000l;
  67         }
  68       else
  69         {
  70           uint64_t i = 0x000fffffffffffffl >> j0;
  71           if ((i0 & i) == 0)
  72             return x;                    /* x is integral */
  73           if (i0 < 0)
  74             i0 += 0x0010000000000000l >> j0;
  75           i0 &= ~i;
  76         }
  77       INSERT_WORDS64 (x, i0);
  78     }
  79   else if (j0 == 0x400)
  80     return x + x;                       /* inf or NaN */
  81   return x;
  82 #endif /* ! USE_FLOOR_BUILTIN  */
  83 }
  84 #ifndef __floor
  85 libm_alias_double (__floor, floor)
  86 #endif