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  * Exception:
  19  *      Inexact flag raised if x not equal to floor(x).
  20  */
  21
  22 #include <math.h>
  23 #include <math_private.h>
  24
  25 static const double huge = 1.0e300;
  26
  27 double
  28 __floor (double x)
  29 {
  30   int32_t i0, i1, j0;
  31   u_int32_t i, j;
  32   EXTRACT_WORDS (i0, i1, x);
  33   j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  34   if (j0 < 20)
  35     {
  36       if (j0 < 0)       /* raise inexact if x != 0 */
  37         {
  38           math_force_eval (huge + x);   /* return 0*sign(x) if |x|<1 */
  39           if (i0 >= 0)
  40             {
  41               i0 = i1 = 0;
  42             }
  43           else if (((i0 & 0x7fffffff) | i1) != 0)
  44             {
  45               i0 = 0xbff00000; i1 = 0;
  46             }
  47         }
  48       else
  49         {
  50           i = (0x000fffff) >> j0;
  51           if (((i0 & i) | i1) == 0)
  52             return x;                        /* x is integral */
  53           math_force_eval (huge + x);           /* raise inexact flag */
  54           if (i0 < 0)
  55             i0 += (0x00100000) >> j0;
  56           i0 &= (~i); i1 = 0;
  57         }
  58     }
  59   else if (j0 > 51)
  60     {
  61       if (j0 == 0x400)
  62         return x + x;                   /* inf or NaN */
  63       else
  64         return x;                       /* x is integral */
  65     }
  66   else
  67     {
  68       i = ((u_int32_t) (0xffffffff)) >> (j0 - 20);
  69       if ((i1 & i) == 0)
  70         return x;                       /* x is integral */
  71       math_force_eval (huge + x);               /* raise inexact flag */
  72       if (i0 < 0)
  73         {
  74           if (j0 == 20)
  75             i0 += 1;
  76           else
  77             {
  78               j = i1 + (1 << (52 - j0));
  79               if (j < i1)
  80                 i0 += 1;                /* got a carry */
  81               i1 = j;
  82             }
  83         }
  84       i1 &= (~i);
  85     }
  86   INSERT_WORDS (x, i0, i1);
  87   return x;
  88 }
  89 #ifndef __floor
  90 weak_alias (__floor, floor)
  91 # ifdef NO_LONG_DOUBLE
  92 strong_alias (__floor, __floorl)
  93 weak_alias (__floor, floorl)
  94 # endif
  95 #endif