xref: /freebsd/lib/msun/src/s_trunc.c (revision 1e413cf93298b5b97441a21d9a50fdcd0ee9945e)
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  * trunc(x)
18  * Return x rounded toward 0 to integral value
19  * Method:
20  *	Bit twiddling.
21  * Exception:
22  *	Inexact flag raised if x not equal to trunc(x).
23  */
24 
25 #include "math.h"
26 #include "math_private.h"
27 
28 static const double huge = 1.0e300;
29 
30 double
31 trunc(double x)
32 {
33 	int32_t i0,i1,j0;
34 	u_int32_t i,j;
35 	EXTRACT_WORDS(i0,i1,x);
36 	j0 = ((i0>>20)&0x7ff)-0x3ff;
37 	if(j0<20) {
38 	    if(j0<0) { 	/* raise inexact if x != 0 */
39 		if(huge+x>0.0) {/* |x|<1, so return 0*sign(x) */
40 		    i0 &= 0x80000000U;
41 		    i1 = 0;
42 		}
43 	    } else {
44 		i = (0x000fffff)>>j0;
45 		if(((i0&i)|i1)==0) return x; /* x is integral */
46 		if(huge+x>0.0) {	/* raise inexact flag */
47 		    i0 &= (~i); i1=0;
48 		}
49 	    }
50 	} else if (j0>51) {
51 	    if(j0==0x400) return x+x;	/* inf or NaN */
52 	    else return x;		/* x is integral */
53 	} else {
54 	    i = ((u_int32_t)(0xffffffff))>>(j0-20);
55 	    if((i1&i)==0) return x;	/* x is integral */
56 	    if(huge+x>0.0)		/* raise inexact flag */
57 		i1 &= (~i);
58 	}
59 	INSERT_WORDS(x,i0,i1);
60 	return x;
61 }
62