Home | History | Annotate | Line # | Download | only in src 
      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 defined(LIBM_SCCS) && !defined(lint)
     15 __RCSID("$NetBSD: s_floor.c,v 1.14 2013/11/11 23:57:34 joerg Exp $");
     16 #endif
     17 
     18 /*
     19  * floor(x)
     20  * Return x rounded toward -inf to integral value
     21  * Method:
     22  *	Bit twiddling.
     23  * Exception:
     24  *	Inexact flag raised if x not equal to floor(x).
     25  */
     26 
     27 #include "math.h"
     28 #include "math_private.h"
     29 
     30 #ifndef __HAVE_LONG_DOUBLE
     31 __strong_alias(_floorl, floor)
     32 __weak_alias(floorl, floor)
     33 #endif
     34 
     35 static const double huge = 1.0e300;
     36 
     37 double
     38 floor(double x)
     39 {
     40 	int32_t i0,i1,jj0;
     41 	u_int32_t i,j;
     42 	EXTRACT_WORDS(i0,i1,x);
     43 	jj0 = ((i0>>20)&0x7ff)-0x3ff;
     44 	if(jj0<20) {
     45 	    if(jj0<0) { 	/* raise inexact if x != 0 */
     46 		if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
     47 		    if(i0>=0) {i0=i1=0;}
     48 		    else if(((i0&0x7fffffff)|i1)!=0)
     49 			{ i0=0xbff00000;i1=0;}
     50 		}
     51 	    } else {
     52 		i = (0x000fffff)>>jj0;
     53 		if(((i0&i)|i1)==0) return x; /* x is integral */
     54 		if(huge+x>0.0) {	/* raise inexact flag */
     55 		    if(i0<0) i0 += (0x00100000)>>jj0;
     56 		    i0 &= (~i); i1=0;
     57 		}
     58 	    }
     59 	} else if (jj0>51) {
     60 	    if(jj0==0x400) return x+x;	/* inf or NaN */
     61 	    else return x;		/* x is integral */
     62 	} else {
     63 	    i = ((u_int32_t)(0xffffffff))>>(jj0-20);
     64 	    if((i1&i)==0) return x;	/* x is integral */
     65 	    if(huge+x>0.0) { 		/* raise inexact flag */
     66 		if(i0<0) {
     67 		    if(jj0==20) i0+=1;
     68 		    else {
     69 			j = i1+(1<<(52-jj0));
     70 			if(j<(u_int32_t)i1) i0 +=1 ; 	/* got a carry */
     71 			i1=j;
     72 		    }
     73 		}
     74 		i1 &= (~i);
     75 	    }
     76 	}
     77 	INSERT_WORDS(x,i0,i1);
     78 	return x;
     79 }
     80