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/* origin: FreeBSD /usr/src/lib/msun/src/s_rint.c */
/*
* ====================================================
* 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 "libm.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;
uint32_t i,i1;
double w,t;
EXTRACT_WORDS(i0, i1, x);
// FIXME: signed shift
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);
STRICT_ASSIGN(double, 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 */
return x; /* x is integral */
} else {
i = (uint32_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);
STRICT_ASSIGN(double, w, TWO52[sx] + x);
return w - TWO52[sx];
}
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