Home | History | Annotate | Download | only in src
      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
     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