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  * From: @(#)s_floor.c 5.1 93/09/24
12  */
13 
14 #include <sys/cdefs.h>
15 __FBSDID("$FreeBSD$");
16 
17 /*
18  * truncl(x)
19  * Return x rounded toward 0 to integral value
20  * Method:
21  *	Bit twiddling.
22  * Exception:
23  *	Inexact flag raised if x not equal to truncl(x).
24  */
25 
26 #include <float.h>
27 #include <math.h>
28 #include <stdint.h>
29 
30 #include "fpmath.h"
31 
32 #ifdef LDBL_IMPLICIT_NBIT
33 #define	MANH_SIZE	(LDBL_MANH_SIZE + 1)
34 #else
35 #define	MANH_SIZE	LDBL_MANH_SIZE
36 #endif
37 
38 static const long double huge = 1.0e300;
39 static const float zero[] = { 0.0, -0.0 };
40 
41 long double
truncl(long double x)42 truncl(long double x)
43 {
44 	union IEEEl2bits u = { .e = x };
45 	int e = u.bits.exp - LDBL_MAX_EXP + 1;
46 
47 	if (e < MANH_SIZE - 1) {
48 		if (e < 0) {			/* raise inexact if x != 0 */
49 			if (huge + x > 0.0)
50 				u.e = zero[u.bits.sign];
51 		} else {
52 			uint64_t m = ((1llu << MANH_SIZE) - 1) >> (e + 1);
53 			if (((u.bits.manh & m) | u.bits.manl) == 0)
54 				return (x);	/* x is integral */
55 			if (huge + x > 0.0) {	/* raise inexact flag */
56 				u.bits.manh &= ~m;
57 				u.bits.manl = 0;
58 			}
59 		}
60 	} else if (e < LDBL_MANT_DIG - 1) {
61 		uint64_t m = (uint64_t)-1 >> (64 - LDBL_MANT_DIG + e + 1);
62 		if ((u.bits.manl & m) == 0)
63 			return (x);	/* x is integral */
64 		if (huge + x > 0.0)		/* raise inexact flag */
65 			u.bits.manl &= ~m;
66 	}
67 	return (u.e);
68 }
69