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

/*
 * floor(x)
 * Return x rounded toward -inf to integral value
 * Method:
 *      Bit twiddling.
 * Exception:
 *      Inexact flag raised if x not equal to floor(x).
 */

#include "math_private.h"

static const double huge = 1.0e300;

double floor(double x)
{
    int32_t i0, i1, j0;
    uint32_t i, j;
    EXTRACT_WORDS(i0, i1, x);
    j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
    if (j0 < 20) {
        if (j0 < 0) {   /* raise inexact if x != 0 */
            if (huge + x > 0.0) {/* return 0*sign(x) if |x|<1 */
                if (i0 >= 0) {
                    i0 = i1 = 0;
                }
                else if (((i0 & 0x7fffffff) | i1) != 0) {
                    i0 = 0xbff00000;
                    i1 = 0;
                }
            }
        }
        else {
            i = (0x000fffff) >> j0;
            if (((i0 & i) | i1) == 0) {
                return x; /* x is integral */
            }
            if (huge + x > 0.0) {       /* raise inexact flag */
                if (i0 < 0) {
                    i0 += (0x00100000) >> j0;
                }
                i0 &= (~i);
                i1 = 0;
            }
        }
    }
    else if (j0 > 51) {
        if (j0 == 0x400) {
            return x + x;       /* inf or NaN */
        }
        else {
            return x;           /* x is integral */
        }
    }
    else {
        i = ((uint32_t) (0xffffffff)) >> (j0 - 20);
        if ((i1 & i)== 0) {
            return x;   /* x is integral */
        }
        if (huge + x > 0.0) {           /* raise inexact flag */
            if (i0 < 0) {
                if (j0 == 20) {
                    i0 += 1;
                }
                else {
                    j = i1 + (1 << (52 - j0));
                    if (j < i1) {
                        i0 += 1 ;       /* got a carry */
                    }
                    i1 = j;
                }
            }
            i1 &= (~i);
        }
    }
    INSERT_WORDS(x, i0, i1);
    return x;
}