sysdeps/ieee754/dbl-64/s_floor.c

   1 /* Round double to integer away from zero.
   2    Copyright (C) 2011-2023 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 /* Based on a version which carries the following copyright:  */
  20
  21 /*
  22  * ====================================================
  23  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
  24  *
  25  * Developed at SunPro, a Sun Microsystems, Inc. business.
  26  * Permission to use, copy, modify, and distribute this
  27  * software is freely granted, provided that this notice
  28  * is preserved.
  29  * ====================================================
  30  */
  31
  32 #define NO_MATH_REDIRECT
  33 #include <math.h>
  34 #include <math_private.h>
  35 #include <stdint.h>
  36 #include <libm-alias-double.h>
  37 #include <math-use-builtins.h>
  38
  39 /*
  40  * floor(x)
  41  * Return x rounded toward -inf to integral value
  42  * Method:
  43  *      Bit twiddling.
  44  */
  45
  46
  47 double
  48 __floor (double x)
  49 {
  50 #if USE_FLOOR_BUILTIN
  51   return __builtin_floor (x);
  52 #else
  53   /* Use generic implementation.  */
  54   int64_t i0;
  55   EXTRACT_WORDS64 (i0, x);
  56   int32_t j0 = ((i0 >> 52) & 0x7ff) - 0x3ff;
  57   if (__glibc_likely (j0 < 52))
  58     {
  59       if (j0 < 0)
  60         {
  61           /* return 0 * sign (x) if |x| < 1  */
  62           if (i0 >= 0)
  63             i0 = 0;
  64           else if ((i0 & 0x7fffffffffffffffl) != 0)
  65             i0 = 0xbff0000000000000l;
  66         }
  67       else
  68         {
  69           uint64_t i = 0x000fffffffffffffl >> j0;
  70           if ((i0 & i) == 0)
  71             return x;                    /* x is integral */
  72           if (i0 < 0)
  73             i0 += 0x0010000000000000l >> j0;
  74           i0 &= ~i;
  75         }
  76       INSERT_WORDS64 (x, i0);
  77     }
  78   else if (j0 == 0x400)
  79     return x + x;                       /* inf or NaN */
  80   return x;
  81 #endif /* ! USE_FLOOR_BUILTIN  */
  82 }
  83 #ifndef __floor
  84 libm_alias_double (__floor, floor)
  85 #endif