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 #include <math.h>
  21 #include <math_private.h>
  22 #include <libm-alias-double.h>
  23
  24 double
  25 __floor (double x)
  26 {
  27   int32_t i0, i1, j0;
  28   uint32_t i, j;
  29   EXTRACT_WORDS (i0, i1, x);
  30   j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  31   if (j0 < 20)
  32     {
  33       if (j0 < 0)
  34         {
  35           /* return 0*sign(x) if |x|<1 */
  36           if (i0 >= 0)
  37             {
  38               i0 = i1 = 0;
  39             }
  40           else if (((i0 & 0x7fffffff) | i1) != 0)
  41             {
  42               i0 = 0xbff00000; i1 = 0;
  43             }
  44         }
  45       else
  46         {
  47           i = (0x000fffff) >> j0;
  48           if (((i0 & i) | i1) == 0)
  49             return x;                        /* x is integral */
  50           if (i0 < 0)
  51             i0 += (0x00100000) >> j0;
  52           i0 &= (~i); i1 = 0;
  53         }
  54     }
  55   else if (j0 > 51)
  56     {
  57       if (j0 == 0x400)
  58         return x + x;                   /* inf or NaN */
  59       else
  60         return x;                       /* x is integral */
  61     }
  62   else
  63     {
  64       i = ((uint32_t) (0xffffffff)) >> (j0 - 20);
  65       if ((i1 & i) == 0)
  66         return x;                       /* x is integral */
  67       if (i0 < 0)
  68         {
  69           if (j0 == 20)
  70             i0 += 1;
  71           else
  72             {
  73               j = i1 + (1 << (52 - j0));
  74               if (j < i1)
  75                 i0 += 1;                /* got a carry */
  76               i1 = j;
  77             }
  78         }
  79       i1 &= (~i);
  80     }
  81   INSERT_WORDS (x, i0, i1);
  82   return x;
  83 }
  84 #ifndef __floor
  85 libm_alias_double (__floor, floor)
  86 #endif