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      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 #include <sys/cdefs.h>
     14 #if 0
     15 __FBSDID("$FreeBSD: src/lib/msun/src/s_trunc.c,v 1.1 2004/06/20 09:25:43 das Exp $");
     16 #endif
     17 #if defined(LIBM_SCCS) && !defined(lint)
     18 __RCSID("$NetBSD: s_trunc.c,v 1.4 2013/11/13 12:58:11 joerg Exp $");
     19 #endif
     20 
     21 /*
     22  * trunc(x)
     23  * Return x rounded toward 0 to integral value
     24  * Method:
     25  *	Bit twiddling.
     26  * Exception:
     27  *	Inexact flag raised if x not equal to trunc(x).
     28  */
     29 
     30 #include "math.h"
     31 #include "math_private.h"
     32 
     33 #ifndef __HAVE_LONG_DOUBLE
     34 __strong_alias(_truncl, trunc)
     35 __weak_alias(truncl, trunc)
     36 #endif
     37 
     38 static const double huge = 1.0e300;
     39 
     40 double
     41 trunc(double x)
     42 {
     43 	int32_t i0,i1,jj0;
     44 	uint32_t i;
     45 	EXTRACT_WORDS(i0,i1,x);
     46 	jj0 = ((i0>>20)&0x7ff)-0x3ff;
     47 	if(jj0<20) {
     48 	    if(jj0<0) { 	/* raise inexact if x != 0 */
     49 		if(huge+x>0.0) {/* |x|<1, so return 0*sign(x) */
     50 		    i0 &= 0x80000000U;
     51 		    i1 = 0;
     52 		}
     53 	    } else {
     54 		i = (0x000fffff)>>jj0;
     55 		if(((i0&i)|i1)==0) return x; /* x is integral */
     56 		if(huge+x>0.0) {	/* raise inexact flag */
     57 		    i0 &= (~i); i1=0;
     58 		}
     59 	    }
     60 	} else if (jj0>51) {
     61 	    if(jj0==0x400) return x+x;	/* inf or NaN */
     62 	    else return x;		/* x is integral */
     63 	} else {
     64 	    i = ((u_int32_t)(0xffffffff))>>(jj0-20);
     65 	    if((i1&i)==0) return x;	/* x is integral */
     66 	    if(huge+x>0.0)		/* raise inexact flag */
     67 		i1 &= (~i);
     68 	}
     69 	INSERT_WORDS(x,i0,i1);
     70 	return x;
     71 }
     72