path: root/src/math/s_floor.c

/* @(#)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).
 */

#include <math.h>
#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;
}