source: soft/giet_vm/giet_libs/math/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.
 * ====================================================
 */

/* Modified for GIET-VM static OS at UPMC, France 2015.
 */

/*
 * 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;
        uint32_t i,i1;
        double t;
        /* We use w = x + 2^52; t = w - 2^52; trick to round x to integer.
         * This trick requires that compiler does not optimize it
         * by keeping intermediate result w in a register wider than double.
         * Declaring w volatile assures that value gets truncated to double
         * (unfortunately, it also forces store+load):
         */
        volatile double w;

        EXTRACT_WORDS(i0,i1,x);
        /* Unbiased exponent */
        j0 = ((((uint32_t)i0) >> 20)&0x7ff)-0x3ff;

        if (j0 > 51) {
                //Why bother? Just returning x works too
                //if (j0 == 0x400)  /* inf or NaN */
                //      return x+x;
                return x;  /* x is integral */
        }

        /* Sign */
        sx = ((uint32_t)i0) >> 31;

        if (j0<20) {
            if (j0<0) { /* |x| < 1 */
                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) {
                    if (j0==19) i1 = 0x40000000;
                    else i0 = (i0&(~i))|((0x20000)>>j0);
                }
            }
        } 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);
        w = TWO52[sx]+x;
        return w-TWO52[sx];
}