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 #include <sys/cdefs.h>
14 __FBSDID("$FreeBSD$");
15 
16 /*
17  * floor(x)
18  * Return x rounded toward -inf to integral value
19  * Method:
20  *	Bit twiddling.
21  * Exception:
22  *	Inexact flag raised if x not equal to floor(x).
23  */
24 
25 #include <float.h>
26 
27 #include "math.h"
28 #include "math_private.h"
29 
30 static const double huge = 1.0e300;
31 
32 double
floor(double x)33 floor(double x)
34 {
35 	int32_t i0,i1,j0;
36 	u_int32_t i,j;
37 	EXTRACT_WORDS(i0,i1,x);
38 	j0 = ((i0>>20)&0x7ff)-0x3ff;
39 	if(j0<20) {
40 	    if(j0<0) { 	/* raise inexact if x != 0 */
41 		if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
42 		    if(i0>=0) {i0=i1=0;}
43 		    else if(((i0&0x7fffffff)|i1)!=0)
44 			{ i0=0xbff00000;i1=0;}
45 		}
46 	    } else {
47 		i = (0x000fffff)>>j0;
48 		if(((i0&i)|i1)==0) return x; /* x is integral */
49 		if(huge+x>0.0) {	/* raise inexact flag */
50 		    if(i0<0) i0 += (0x00100000)>>j0;
51 		    i0 &= (~i); i1=0;
52 		}
53 	    }
54 	} else if (j0>51) {
55 	    if(j0==0x400) return x+x;	/* inf or NaN */
56 	    else return x;		/* x is integral */
57 	} else {
58 	    i = ((u_int32_t)(0xffffffff))>>(j0-20);
59 	    if((i1&i)==0) return x;	/* x is integral */
60 	    if(huge+x>0.0) { 		/* raise inexact flag */
61 		if(i0<0) {
62 		    if(j0==20) i0+=1;
63 		    else {
64 			j = i1+(1<<(52-j0));
65 			if(j<i1) i0 +=1 ; 	/* got a carry */
66 			i1=j;
67 		    }
68 		}
69 		i1 &= (~i);
70 	    }
71 	}
72 	INSERT_WORDS(x,i0,i1);
73 	return x;
74 }
75 
76 #if LDBL_MANT_DIG == 53
77 __weak_reference(floor, floorl);
78 #endif
79