sysdeps/ieee754/dbl-64/s_floor.c

   1 /* @(#)s_floor.c 5.1 93/09/24 */
   2 /*
   3  * ====================================================
   4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   5  *
   6  * Developed at SunPro, a Sun Microsystems, Inc. business.
   7  * Permission to use, copy, modify, and distribute this
   8  * software is freely granted, provided that this notice
   9  * is preserved.
  10  * ====================================================
  11  */
  12
  13 /*
  14  * floor(x)
  15  * Return x rounded toward -inf to integral value
  16  * Method:
  17  *      Bit twiddling.
  18  */
  19
  20 #define NO_MATH_REDIRECT
  21 #include <math.h>
  22 #include <math_private.h>
  23 #include <libm-alias-double.h>
  24
  25 double
  26 __floor (double x)
  27 {
  28   int32_t i0, i1, j0;
  29   uint32_t i, j;
  30   EXTRACT_WORDS (i0, i1, x);
  31   j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  32   if (j0 < 20)
  33     {
  34       if (j0 < 0)
  35         {
  36           /* return 0*sign(x) if |x|<1 */
  37           if (i0 >= 0)
  38             {
  39               i0 = i1 = 0;
  40             }
  41           else if (((i0 & 0x7fffffff) | i1) != 0)
  42             {
  43               i0 = 0xbff00000; i1 = 0;
  44             }
  45         }
  46       else
  47         {
  48           i = (0x000fffff) >> j0;
  49           if (((i0 & i) | i1) == 0)
  50             return x;                        /* x is integral */
  51           if (i0 < 0)
  52             i0 += (0x00100000) >> j0;
  53           i0 &= (~i); i1 = 0;
  54         }
  55     }
  56   else if (j0 > 51)
  57     {
  58       if (j0 == 0x400)
  59         return x + x;                   /* inf or NaN */
  60       else
  61         return x;                       /* x is integral */
  62     }
  63   else
  64     {
  65       i = ((uint32_t) (0xffffffff)) >> (j0 - 20);
  66       if ((i1 & i) == 0)
  67         return x;                       /* x is integral */
  68       if (i0 < 0)
  69         {
  70           if (j0 == 20)
  71             i0 += 1;
  72           else
  73             {
  74               j = i1 + (1 << (52 - j0));
  75               if (j < i1)
  76                 i0 += 1;                /* got a carry */
  77               i1 = j;
  78             }
  79         }
  80       i1 &= (~i);
  81     }
  82   INSERT_WORDS (x, i0, i1);
  83   return x;
  84 }
  85 #ifndef __floor
  86 libm_alias_double (__floor, floor)
  87 #endif