xref: /freebsd/lib/msun/src/s_truncl.c (revision 7c43148a974877188a930e4078a164f83da8e652)
1 /*
2  * ====================================================
3  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
4  *
5  * Developed at SunPro, a Sun Microsystems, Inc. business.
6  * Permission to use, copy, modify, and distribute this
7  * software is freely granted, provided that this notice
8  * is preserved.
9  * ====================================================
10  */
11 
12 #include <sys/cdefs.h>
13 /*
14  * truncl(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 truncl(x).
20  */
21 
22 #include <float.h>
23 #include <math.h>
24 #include <stdint.h>
25 
26 #include "fpmath.h"
27 
28 #ifdef LDBL_IMPLICIT_NBIT
29 #define	MANH_SIZE	(LDBL_MANH_SIZE + 1)
30 #else
31 #define	MANH_SIZE	LDBL_MANH_SIZE
32 #endif
33 
34 static const long double huge = 1.0e300;
35 static const float zero[] = { 0.0, -0.0 };
36 
37 long double
38 truncl(long double x)
39 {
40 	union IEEEl2bits u = { .e = x };
41 	int e = u.bits.exp - LDBL_MAX_EXP + 1;
42 
43 	if (e < MANH_SIZE - 1) {
44 		if (e < 0) {			/* raise inexact if x != 0 */
45 			if (huge + x > 0.0)
46 				u.e = zero[u.bits.sign];
47 		} else {
48 			uint64_t m = ((1llu << MANH_SIZE) - 1) >> (e + 1);
49 			if (((u.bits.manh & m) | u.bits.manl) == 0)
50 				return (x);	/* x is integral */
51 			if (huge + x > 0.0) {	/* raise inexact flag */
52 				u.bits.manh &= ~m;
53 				u.bits.manl = 0;
54 			}
55 		}
56 	} else if (e < LDBL_MANT_DIG - 1) {
57 		uint64_t m = (uint64_t)-1 >> (64 - LDBL_MANT_DIG + e + 1);
58 		if ((u.bits.manl & m) == 0)
59 			return (x);	/* x is integral */
60 		if (huge + x > 0.0)		/* raise inexact flag */
61 			u.bits.manl &= ~m;
62 	}
63 	return (u.e);
64 }
65