s_floor.c

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/* @(#)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,jj0;
    u_int32_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 = ((u_int32_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<i1) i0 +=1 ;   /* got a carry */
            i1=j;
            }
        }
        i1 &= (~i);
        }
    }
    INSERT_WORDS(x,i0,i1);
    return x;
}