1
2/* @(#)s_floor.c 1.3 95/01/18 */
3/*
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6 *
7 * Developed at SunSoft, a Sun Microsystems, Inc. business.
8 * Permission to use, copy, modify, and distribute this
9 * software is freely granted, provided that this notice
10 * is preserved.
11 * ====================================================
12 */
13
14/*
15 * ieee_floor(x)
16 * Return x rounded toward -inf to integral value
17 * Method:
18 *	Bit twiddling.
19 * Exception:
20 *	Inexact flag raised if x not equal to ieee_floor(x).
21 */
22
23#include "fdlibm.h"
24
25#ifdef __STDC__
26static const double huge = 1.0e300;
27#else
28static double huge = 1.0e300;
29#endif
30
31#ifdef __STDC__
32	double ieee_floor(double x)
33#else
34	double ieee_floor(x)
35	double x;
36#endif
37{
38	int i0,i1,j0;
39	unsigned i,j;
40	i0 =  __HI(x);
41	i1 =  __LO(x);
42	j0 = ((i0>>20)&0x7ff)-0x3ff;
43	if(j0<20) {
44	    if(j0<0) { 	/* raise inexact if x != 0 */
45		if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
46		    if(i0>=0) {i0=i1=0;}
47		    else if(((i0&0x7fffffff)|i1)!=0)
48			{ i0=0xbff00000;i1=0;}
49		}
50	    } else {
51		i = (0x000fffff)>>j0;
52		if(((i0&i)|i1)==0) return x; /* x is integral */
53		if(huge+x>0.0) {	/* raise inexact flag */
54		    if(i0<0) i0 += (0x00100000)>>j0;
55		    i0 &= (~i); i1=0;
56		}
57	    }
58	} else if (j0>51) {
59	    if(j0==0x400) return x+x;	/* inf or NaN */
60	    else return x;		/* x is integral */
61	} else {
62	    i = ((unsigned)(0xffffffff))>>(j0-20);
63	    if((i1&i)==0) return x;	/* x is integral */
64	    if(huge+x>0.0) { 		/* raise inexact flag */
65		if(i0<0) {
66		    if(j0==20) i0+=1;
67		    else {
68			j = i1+(1<<(52-j0));
69			if(j<i1) i0 +=1 ; 	/* got a carry */
70			i1=j;
71		    }
72		}
73		i1 &= (~i);
74	    }
75	}
76	__HI(x) = i0;
77	__LO(x) = i1;
78	return x;
79}
80