xref: /minix3/lib/libm/src/s_floor.c (revision 84d9c625bfea59e274550651111ae9edfdc40fbd)
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 #if defined(LIBM_SCCS) && !defined(lint)
15 __RCSID("$NetBSD: s_floor.c,v 1.14 2013/11/11 23:57:34 joerg Exp $");
16 #endif
17 
18 /*
19  * floor(x)
20  * Return x rounded toward -inf to integral value
21  * Method:
22  *	Bit twiddling.
23  * Exception:
24  *	Inexact flag raised if x not equal to floor(x).
25  */
26 
27 #include "math.h"
28 #include "math_private.h"
29 
30 #ifndef __HAVE_LONG_DOUBLE
31 __strong_alias(_floorl, floor)
32 __weak_alias(floorl, floor)
33 #endif
34 
35 static const double huge = 1.0e300;
36 
37 double
floor(double x)38 floor(double x)
39 {
40 	int32_t i0,i1,jj0;
41 	u_int32_t i,j;
42 	EXTRACT_WORDS(i0,i1,x);
43 	jj0 = ((i0>>20)&0x7ff)-0x3ff;
44 	if(jj0<20) {
45 	    if(jj0<0) { 	/* raise inexact if x != 0 */
46 		if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
47 		    if(i0>=0) {i0=i1=0;}
48 		    else if(((i0&0x7fffffff)|i1)!=0)
49 			{ i0=0xbff00000;i1=0;}
50 		}
51 	    } else {
52 		i = (0x000fffff)>>jj0;
53 		if(((i0&i)|i1)==0) return x; /* x is integral */
54 		if(huge+x>0.0) {	/* raise inexact flag */
55 		    if(i0<0) i0 += (0x00100000)>>jj0;
56 		    i0 &= (~i); i1=0;
57 		}
58 	    }
59 	} else if (jj0>51) {
60 	    if(jj0==0x400) return x+x;	/* inf or NaN */
61 	    else return x;		/* x is integral */
62 	} else {
63 	    i = ((u_int32_t)(0xffffffff))>>(jj0-20);
64 	    if((i1&i)==0) return x;	/* x is integral */
65 	    if(huge+x>0.0) { 		/* raise inexact flag */
66 		if(i0<0) {
67 		    if(jj0==20) i0+=1;
68 		    else {
69 			j = i1+(1<<(52-jj0));
70 			if(j<(u_int32_t)i1) i0 +=1 ; 	/* got a carry */
71 			i1=j;
72 		    }
73 		}
74 		i1 &= (~i);
75 	    }
76 	}
77 	INSERT_WORDS(x,i0,i1);
78 	return x;
79 }
80