floor.c

/*
 *                               POK header
 * 
 * The following file is a part of the POK project. Any modification should
 * made according to the POK licence. You CANNOT use this file or a part of
 * this file is this part of a file for your own project
 *
 * For more information on the POK licence, please see our LICENCE FILE
 *
 * Please follow the coding guidelines described in doc/CODING_GUIDELINES
 *
 *                                      Copyright (c) 2007-2009 POK team 
 *
 * Created by julien on Fri Jan 30 14:41:34 2009 
 */

/* @(#)s_floor.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.
 * ====================================================
 */

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

#ifdef POK_NEEDS_LIBMATH

#include "math_private.h"

static const double huge = 1.0e300;

double
floor(double x)
{
        int32_t i0,i1,jj0;
        uint32_t i,j;
        EXTRACT_WORDS(i0,i1,x);
        jj0 = ((i0>>20)&0x7ff)-0x3ff;
        if(jj0<20) {
            if(jj0<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)>>jj0;
                if(((i0&i)|i1)==0) return x; /* x is integral */
                if(huge+x>0.0) {        /* raise inexact flag */
                    if(i0<0) i0 += (0x00100000)>>jj0;
                    i0 &= (~i); i1=0;
                }
            }
        } else if (jj0>51) {
            if(jj0==0x400) return x+x;  /* inf or NaN */
            else return x;              /* x is integral */
        } else {
            i = ((uint32_t)(0xffffffff))>>(jj0-20);
            if((i1&i)==0) return x;     /* x is integral */
            if(huge+x>0.0) {            /* raise inexact flag */
                if(i0<0) {
                    if(jj0==20) i0+=1;
                    else {
                        j = i1+(1<<(52-jj0));
                        if(j<(uint32_t)i1) i0 +=1 ;     /* got a carry */
                        i1=j;
                    }
                }
                i1 &= (~i);
            }
        }
        INSERT_WORDS(x,i0,i1);
        return x;
}

#endif