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__
26 static const double huge = 1.0e300;
27 #else
28 static double huge = 1.0e300;
29 #endif
30 
31 #ifdef __STDC__
ieee_floor(double x)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