sysdeps/ieee754/dbl-64/s_rint.c

   1 /*
   2  * ====================================================
   3  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   4  *
   5  * Developed at SunPro, a Sun Microsystems, Inc. business.
   6  * Permission to use, copy, modify, and distribute this
   7  * software is freely granted, provided that this notice
   8  * is preserved.
   9  * ====================================================
  10  */
  11
  12 /*
  13  * rint(x)
  14  * Return x rounded to integral value according to the prevailing
  15  * rounding mode.
  16  * Method:
  17  *      Using floating addition.
  18  * Exception:
  19  *      Inexact flag raised if x not equal to rint(x).
  20  */
  21
  22 #define NO_MATH_REDIRECT
  23 #include <math.h>
  24 #include <math_private.h>
  25 #include <libm-alias-double.h>
  26 #include <math-use-builtins.h>
  27
  28 double
  29 __rint (double x)
  30 {
  31 #if USE_RINT_BUILTIN
  32   return __builtin_rint (x);
  33 #else
  34   /* Use generic implementation.  */
  35   static const double
  36     TWO52[2] = {
  37                 4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
  38                 -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
  39   };
  40   int64_t i0, sx;
  41   int32_t j0;
  42   EXTRACT_WORDS64 (i0, x);
  43   sx = (i0 >> 63) & 1;
  44   j0 = ((i0 >> 52) & 0x7ff) - 0x3ff;
  45   if (j0 < 52)
  46     {
  47       if (j0 < 0)
  48         {
  49           double w = TWO52[sx] + x;
  50           double t =  w - TWO52[sx];
  51           EXTRACT_WORDS64 (i0, t);
  52           INSERT_WORDS64 (t, (i0 & UINT64_C (0x7fffffffffffffff))
  53                           | (sx << 63));
  54           return t;
  55         }
  56     }
  57   else
  58     {
  59       if (j0 == 0x400)
  60         return x + x;                   /* inf or NaN  */
  61       else
  62         return x;                       /* x is integral  */
  63     }
  64   double w = TWO52[sx] + x;
  65   return w - TWO52[sx];
  66 #endif /* ! USE_RINT_BUILTIN  */
  67 }
  68 #ifndef __rint
  69 libm_alias_double (__rint, rint)
  70 #endif