s_rint.c

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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.
 * ====================================================
 */

/*
 * 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 <sys/cdefs.h>
#include <float.h>
#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,jj0,sx;
    u_int32_t i,i1;
    double w,t;
    EXTRACT_WORDS(i0,i1,x);
    sx = (i0>>31)&1;
    jj0 = ((i0>>20)&0x7ff)-0x3ff;
    if(jj0<20) {
        if(jj0<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)>>jj0;
        if(((i0&i)|i1)==0) return x; /* x is integral */
        i>>=1;
        if(((i0&i)|i1)!=0) {
            if(jj0==19) i1 = 0x40000000; else
            i0 = (i0&(~i))|((0x20000)>>jj0);
        }
        }
    } else if (jj0>51) {
        if(jj0==0x400) return x+x;  /* inf or NaN */
        else return x;      /* x is integral */
    } else {
        i = ((u_int32_t)(0xffffffff))>>(jj0-20);
        if((i1&i)==0) return x; /* x is integral */
        i>>=1;
        if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(jj0-20));
    }
    INSERT_WORDS(x,i0,i1);
    w = TWO52[sx]+x;
    return w-TWO52[sx];
}

#if LDBL_MANT_DIG == 53
#ifdef __weak_alias
__weak_alias(rintl, rint);
#endif /* __weak_alias */
#endif /* LDBL_MANT_DIG == 53 */