nsz Git - musl/blob - src/math/s_rint.c

   1 /* @(#)s_rint.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  * rint(x)
  15  * Return x rounded to integral value according to the prevailing
  16  * rounding mode.
  17  * Method:
  18  *      Using floating addition.
  19  * Exception:
  20  *      Inexact flag raised if x not equal to rint(x).
  21  */
  22
  23 #include <math.h>
  24 #include "math_private.h"
  25
  26 /*
  27  * TWO23 is long double instead of double to avoid a bug in gcc.  Without
  28  * this, gcc thinks that TWO23[sx]+x and w-TWO23[sx] already have double
  29  * precision and doesn't clip them to double precision when they are
  30  * assigned and returned.
  31  */
  32 static const long double
  33 TWO52[2]={
  34   4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
  35  -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
  36 };
  37
  38 double
  39 rint(double x)
  40 {
  41         int32_t i0,j0,sx;
  42         uint32_t i,i1;
  43         double w,t;
  44         EXTRACT_WORDS(i0,i1,x);
  45         sx = (i0>>31)&1;
  46         j0 = ((i0>>20)&0x7ff)-0x3ff;
  47         if(j0<20) {
  48             if(j0<0) {
  49                 if(((i0&0x7fffffff)|i1)==0) return x;
  50                 i1 |= (i0&0x0fffff);
  51                 i0 &= 0xfffe0000;
  52                 i0 |= ((i1|-i1)>>12)&0x80000;
  53                 SET_HIGH_WORD(x,i0);
  54                 w = TWO52[sx]+x;
  55                 t =  w-TWO52[sx];
  56                 GET_HIGH_WORD(i0,t);
  57                 SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
  58                 return t;
  59             } else {
  60                 i = (0x000fffff)>>j0;
  61                 if(((i0&i)|i1)==0) return x; /* x is integral */
  62                 i>>=1;
  63                 if(((i0&i)|i1)!=0) {
  64                     if(j0==19) i1 = 0x40000000; else
  65                     i0 = (i0&(~i))|((0x20000)>>j0);
  66                 }
  67             }
  68         } else if (j0>51) {
  69             if(j0==0x400) return x+x;   /* inf or NaN */
  70             else return x;              /* x is integral */
  71         } else {
  72             i = ((uint32_t)(0xffffffff))>>(j0-20);
  73             if((i1&i)==0) return x;     /* x is integral */
  74             i>>=1;
  75             if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
  76         }
  77         INSERT_WORDS(x,i0,i1);
  78         w = TWO52[sx]+x;
  79         return w-TWO52[sx];
  80 }