s_floor.c revision 117912 
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[] = "$FreeBSD: head/lib/msun/src/s_floor.c 117912 2003-07-23 04:53:47Z peter $";
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
29static const double huge = 1.0e300;
30
31double
32floor(double x)
33{
34	int32_t i0,i1,j0;
35	u_int32_t i,j;
36	EXTRACT_WORDS(i0,i1,x);
37	j0 = ((i0>>20)&0x7ff)-0x3ff;
38	if(j0<20) {
39	    if(j0<0) { 	/* raise inexact if x != 0 */
40		if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
41		    if(i0>=0) {i0=i1=0;}
42		    else if(((i0&0x7fffffff)|i1)!=0)
43			{ i0=0xbff00000;i1=0;}
44		}
45	    } else {
46		i = (0x000fffff)>>j0;
47		if(((i0&i)|i1)==0) return x; /* x is integral */
48		if(huge+x>0.0) {	/* raise inexact flag */
49		    if(i0<0) i0 += (0x00100000)>>j0;
50		    i0 &= (~i); i1=0;
51		}
52	    }
53	} else if (j0>51) {
54	    if(j0==0x400) return x+x;	/* inf or NaN */
55	    else return x;		/* x is integral */
56	} else {
57	    i = ((u_int32_t)(0xffffffff))>>(j0-20);
58	    if((i1&i)==0) return x;	/* x is integral */
59	    if(huge+x>0.0) { 		/* raise inexact flag */
60		if(i0<0) {
61		    if(j0==20) i0+=1;
62		    else {
63			j = i1+(1<<(52-j0));
64			if(j<i1) i0 +=1 ; 	/* got a carry */
65			i1=j;
66		    }
67		}
68		i1 &= (~i);
69	    }
70	}
71	INSERT_WORDS(x,i0,i1);
72	return x;
73}
74