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      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 #include <sys/cdefs.h>
     14 #if defined(LIBM_SCCS) && !defined(lint)
     15 __RCSID("$NetBSD: s_rint.c,v 1.13 2022/08/28 21:24:09 he Exp $");
     16 #endif
     17 
     18 /*
     19  * rint(x)
     20  * Return x rounded to integral value according to the prevailing
     21  * rounding mode.
     22  * Method:
     23  *	Using floating addition.
     24  * Exception:
     25  *	Inexact flag raised if x not equal to rint(x).
     26  */
     27 
     28 #include "math.h"
     29 #include "math_private.h"
     30 
     31 static const double
     32 TWO52[2]={
     33   4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
     34  -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
     35 };
     36 
     37 double
     38 rint(double x)
     39 {
     40 	int32_t i0,jj0,sx;
     41 	u_int32_t i,i1;
     42 	double w,t;
     43 	EXTRACT_WORDS(i0,i1,x);
     44 	sx = (i0>>31)&1;
     45 	jj0 = ((i0>>20)&0x7ff)-0x3ff;
     46 	if(jj0<20) {
     47 	    if(jj0<0) {
     48 		if(((i0&0x7fffffff)|i1)==0) return x;
     49 		i1 |= (i0&0x0fffff);
     50 		i0 &= 0xfffe0000;
     51 		i0 |= ((i1|-i1)>>12)&0x80000;
     52 		SET_HIGH_WORD(x,i0);
     53 	        w = TWO52[sx]+x;
     54 	        t =  w-TWO52[sx];
     55 		GET_HIGH_WORD(i0,t);
     56 		SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
     57 	        return t;
     58 	    } else {
     59 		i = (0x000fffff)>>jj0;
     60 		if(((i0&i)|i1)==0) return x; /* x is integral */
     61 		i>>=1;
     62 		if(((i0&i)|i1)!=0) {
     63 		    if(jj0==19) i1 = 0x40000000; else
     64 		    i0 = (i0&(~i))|((0x20000)>>jj0);
     65 		}
     66 	    }
     67 	} else if (jj0>51) {
     68 	    if(jj0==0x400) return x+x;	/* inf or NaN */
     69 	    else return x;		/* x is integral */
     70 	} else {
     71 	    i = ((u_int32_t)(0xffffffff))>>(jj0-20);
     72 	    if((i1&i)==0) return x;	/* x is integral */
     73 	    i>>=1;
     74 	    if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(jj0-20));
     75 	}
     76 	INSERT_WORDS(x,i0,i1);
     77 	w = TWO52[sx]+x;
     78 	return w-TWO52[sx];
     79 }
     80 
     81 #if !defined(__HAVE_LONG_DOUBLE)
     82 __weak_alias(rintl, rint)
     83 #endif
     84