s_floor.c revision 22993 
1/* @(#)s_floor.c 5.1 93/09/24 */
2/*
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5 *
6 * Developed at SunPro, a Sun Microsystems, Inc. business.
7 * Permission to use, copy, modify, and distribute this
8 * software is freely granted, provided that this notice
9 * is preserved.
10 * ====================================================
11 */
12
13#ifndef lint
14static char rcsid[] = "$Id$";
15#endif
16
17/*
18 * floor(x)
19 * Return x rounded toward -inf to integral value
20 * Method:
21 *	Bit twiddling.
22 * Exception:
23 *	Inexact flag raised if x not equal to floor(x).
24 */
25
26#include "math.h"
27#include "math_private.h"
28
29#ifdef __STDC__
30static const double huge = 1.0e300;
31#else
32static double huge = 1.0e300;
33#endif
34
35#ifdef __STDC__
36	double __generic_floor(double x)
37#else
38	double __generic_floor(x)
39	double x;
40#endif
41{
42	int32_t i0,i1,j0;
43	u_int32_t i,j;
44	EXTRACT_WORDS(i0,i1,x);
45	j0 = ((i0>>20)&0x7ff)-0x3ff;
46	if(j0<20) {
47	    if(j0<0) { 	/* raise inexact if x != 0 */
48		if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
49		    if(i0>=0) {i0=i1=0;}
50		    else if(((i0&0x7fffffff)|i1)!=0)
51			{ i0=0xbff00000;i1=0;}
52		}
53	    } else {
54		i = (0x000fffff)>>j0;
55		if(((i0&i)|i1)==0) return x; /* x is integral */
56		if(huge+x>0.0) {	/* raise inexact flag */
57		    if(i0<0) i0 += (0x00100000)>>j0;
58		    i0 &= (~i); i1=0;
59		}
60	    }
61	} else if (j0>51) {
62	    if(j0==0x400) return x+x;	/* inf or NaN */
63	    else return x;		/* x is integral */
64	} else {
65	    i = ((u_int32_t)(0xffffffff))>>(j0-20);
66	    if((i1&i)==0) return x;	/* x is integral */
67	    if(huge+x>0.0) { 		/* raise inexact flag */
68		if(i0<0) {
69		    if(j0==20) i0+=1;
70		    else {
71			j = i1+(1<<(52-j0));
72			if(j<i1) i0 +=1 ; 	/* got a carry */
73			i1=j;
74		    }
75		}
76		i1 &= (~i);
77	    }
78	}
79	INSERT_WORDS(x,i0,i1);
80	return x;
81}
82