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/* @(#)s_rint.c 5.1 93/09/24 */
/*
* ====================================================
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
*
* Developed at SunPro, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*/
#ifndef lint
static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_rint.c,v 1.13 2005/12/03 07:38:35 bde Exp $";
#endif
/*
* rint(x)
* Return x rounded to integral value according to the prevailing
* rounding mode.
* Method:
* Using floating addition.
* Exception:
* Inexact flag raised if x not equal to rint(x).
*/
#include "math.h"
#include "math_private.h"
static const double
TWO52[2]={
4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
-4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
};
double
rint(double x)
{
int32_t i0,j0,sx;
u_int32_t i,i1;
double w,t;
EXTRACT_WORDS(i0,i1,x);
sx = (i0>>31)&1;
j0 = ((i0>>20)&0x7ff)-0x3ff;
if(j0<20) {
if(j0<0) {
if(((i0&0x7fffffff)|i1)==0) return x;
i1 |= (i0&0x0fffff);
i0 &= 0xfffe0000;
i0 |= ((i1|-i1)>>12)&0x80000;
SET_HIGH_WORD(x,i0);
w = TWO52[sx]+x;
t = w-TWO52[sx];
GET_HIGH_WORD(i0,t);
SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
return t;
} else {
i = (0x000fffff)>>j0;
if(((i0&i)|i1)==0) return x; /* x is integral */
i>>=1;
if(((i0&i)|i1)!=0) {
/*
* Some bit is set after the 0.5 bit. To avoid the
* possibility of errors from double rounding in
* w = TWO52[sx]+x, adjust the 0.25 bit to a lower
* guard bit. We do this for all j0<=51. The
* adjustment is trickiest for j0==18 and j0==19
* since then it spans the word boundary.
*/
if(j0==19) i1 = 0x40000000; else
if(j0==18) i1 = 0x80000000; else
i0 = (i0&(~i))|((0x20000)>>j0);
}
}
} else if (j0>51) {
if(j0==0x400) return x+x; /* inf or NaN */
else return x; /* x is integral */
} else {
i = ((u_int32_t)(0xffffffff))>>(j0-20);
if((i1&i)==0) return x; /* x is integral */
i>>=1;
if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
}
INSERT_WORDS(x,i0,i1);
*(volatile double *)&w = TWO52[sx]+x; /* clip any extra precision */
return w-TWO52[sx];
}
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