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 /*
14  * trunc(x)
15  * Return x rounded toward 0 to integral value
16  * Method:
17  *	Bit twiddling.
18  * Exception:
19  *	Inexact flag raised if x not equal to trunc(x).
20  */
21 
22 #include <float.h>
23 #include <math.h>
24 
25 #include "math_private.h"
26 
27 static const double huge = 1.0e300;
28 
29 double
30 trunc(double x)
31 {
32 	int32_t i0,i1,jj0;
33 	u_int32_t i;
34 	EXTRACT_WORDS(i0,i1,x);
35 	jj0 = ((i0>>20)&0x7ff)-0x3ff;
36 	if(jj0<20) {
37 	    if(jj0<0) { 	/* raise inexact if x != 0 */
38 		if(huge+x>0.0) {/* |x|<1, so return 0*sign(x) */
39 		    i0 &= 0x80000000U;
40 		    i1 = 0;
41 		}
42 	    } else {
43 		i = (0x000fffff)>>jj0;
44 		if(((i0&i)|i1)==0) return x; /* x is integral */
45 		if(huge+x>0.0) {	/* raise inexact flag */
46 		    i0 &= (~i); i1=0;
47 		}
48 	    }
49 	} else if (jj0>51) {
50 	    if(jj0==0x400) return x+x;	/* inf or NaN */
51 	    else return x;		/* x is integral */
52 	} else {
53 	    i = ((u_int32_t)(0xffffffff))>>(jj0-20);
54 	    if((i1&i)==0) return x;	/* x is integral */
55 	    if(huge+x>0.0)		/* raise inexact flag */
56 		i1 &= (~i);
57 	}
58 	INSERT_WORDS(x,i0,i1);
59 	return x;
60 }
61 
62 #if	LDBL_MANT_DIG == DBL_MANT_DIG
63 __strong_alias(truncl, trunc);
64 #endif	/* LDBL_MANT_DIG == DBL_MANT_DIG */
65