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      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 __RCSID("$NetBSD: s_truncl.c,v 1.4 2013/11/13 12:58:11 joerg Exp $");
     16 #if 0
     17 __FBSDID("$FreeBSD: head/lib/msun/src/s_truncl.c 176280 2008-02-14 15:10:34Z bde $");
     18 #endif
     19 
     20 /*
     21  * truncl(x)
     22  * Return x rounded toward 0 to integral value
     23  * Method:
     24  *	Bit twiddling.
     25  * Exception:
     26  *	Inexact flag raised if x not equal to truncl(x).
     27  */
     28 #include "namespace.h"
     29 
     30 #include <float.h>
     31 #include <math.h>
     32 #include <stdint.h>
     33 #include <machine/ieee.h>
     34 
     35 #ifdef __HAVE_LONG_DOUBLE
     36 
     37 #ifdef __weak_alias
     38 __weak_alias(truncl, _truncl)
     39 #endif
     40 
     41 #ifdef LDBL_IMPLICIT_NBIT
     42 #define	MANH_SIZE	(EXT_FRACHBITS + 1)
     43 #else
     44 #define	MANH_SIZE	EXT_FRACHBITS
     45 #endif
     46 
     47 static const long double huge = 1.0e300;
     48 static const float zero[] = { 0.0, -0.0 };
     49 
     50 long double
     51 truncl(long double x)
     52 {
     53 	union ieee_ext_u ux = { .extu_ld = x, };
     54 	int e = ux.extu_exp - LDBL_MAX_EXP + 1;
     55 
     56 	if (e < MANH_SIZE - 1) {
     57 		if (e < 0) {			/* raise inexact if x != 0 */
     58 			if (huge + x > 0.0)
     59 				ux.extu_ld = zero[ux.extu_sign];
     60 		} else {
     61 			uint64_t m = ((1llu << MANH_SIZE) - 1) >> (e + 1);
     62 			if (((ux.extu_frach & m) | ux.extu_fracl) == 0)
     63 				return (x);	/* x is integral */
     64 			if (huge + x > 0.0) {	/* raise inexact flag */
     65 				ux.extu_frach &= ~m;
     66 				ux.extu_fracl = 0;
     67 			}
     68 		}
     69 	} else if (e < LDBL_MANT_DIG - 1) {
     70 		uint64_t m = (uint64_t)-1 >> (64 - LDBL_MANT_DIG + e + 1);
     71 		if ((ux.extu_fracl & m) == 0)
     72 			return (x);	/* x is integral */
     73 		if (huge + x > 0.0)		/* raise inexact flag */
     74 			ux.extu_fracl &= ~m;
     75 	}
     76 	return (ux.extu_ld);
     77 }
     78 
     79 #endif /* __HAVE_LONG_DOUBLE */
     80