xref: /freebsd/lib/msun/src/s_floor.c (revision 264104f26834fdb27974e0c5fdedf8f2f5a90383)
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  __FBSDID("$FreeBSD$");
15  
16  /*
17   * floor(x)
18   * Return x rounded toward -inf to integral value
19   * Method:
20   *	Bit twiddling.
21   * Exception:
22   *	Inexact flag raised if x not equal to floor(x).
23   */
24  
25  #include <float.h>
26  
27  #include "math.h"
28  #include "math_private.h"
29  
30  static const double huge = 1.0e300;
31  
32  double
33  floor(double x)
34  {
35  	int32_t i0,i1,j0;
36  	u_int32_t i,j;
37  	EXTRACT_WORDS(i0,i1,x);
38  	j0 = ((i0>>20)&0x7ff)-0x3ff;
39  	if(j0<20) {
40  	    if(j0<0) { 	/* raise inexact if x != 0 */
41  		if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
42  		    if(i0>=0) {i0=i1=0;}
43  		    else if(((i0&0x7fffffff)|i1)!=0)
44  			{ i0=0xbff00000;i1=0;}
45  		}
46  	    } else {
47  		i = (0x000fffff)>>j0;
48  		if(((i0&i)|i1)==0) return x; /* x is integral */
49  		if(huge+x>0.0) {	/* raise inexact flag */
50  		    if(i0<0) i0 += (0x00100000)>>j0;
51  		    i0 &= (~i); i1=0;
52  		}
53  	    }
54  	} else if (j0>51) {
55  	    if(j0==0x400) return x+x;	/* inf or NaN */
56  	    else return x;		/* x is integral */
57  	} else {
58  	    i = ((u_int32_t)(0xffffffff))>>(j0-20);
59  	    if((i1&i)==0) return x;	/* x is integral */
60  	    if(huge+x>0.0) { 		/* raise inexact flag */
61  		if(i0<0) {
62  		    if(j0==20) i0+=1;
63  		    else {
64  			j = i1+(1<<(52-j0));
65  			if(j<i1) i0 +=1 ; 	/* got a carry */
66  			i1=j;
67  		    }
68  		}
69  		i1 &= (~i);
70  	    }
71  	}
72  	INSERT_WORDS(x,i0,i1);
73  	return x;
74  }
75  
76  #if LDBL_MANT_DIG == 53
77  __weak_reference(floor, floorl);
78  #endif
79