xref: /freebsd/lib/msun/src/s_floor.c (revision e37e8677fe55ddd0685c764e17ac58707787758a)
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 
12 #include <sys/cdefs.h>
13 /*
14  * floor(x)
15  * Return x rounded toward -inf to integral value
16  * Method:
17  *	Bit twiddling.
18  * Exception:
19  *	Inexact flag raised if x not equal to floor(x).
20  */
21 
22 #include <float.h>
23 
24 #include "math.h"
25 #include "math_private.h"
26 
27 static const double huge = 1.0e300;
28 
29 double
30 floor(double x)
31 {
32 	int32_t i0,i1,j0;
33 	u_int32_t i,j;
34 	EXTRACT_WORDS(i0,i1,x);
35 	j0 = ((i0>>20)&0x7ff)-0x3ff;
36 	if(j0<20) {
37 	    if(j0<0) { 	/* raise inexact if x != 0 */
38 		if(huge+x>0.0) {/* return 0*sign(x) if |x|<1 */
39 		    if(i0>=0) {i0=i1=0;}
40 		    else if(((i0&0x7fffffff)|i1)!=0)
41 			{ i0=0xbff00000;i1=0;}
42 		}
43 	    } else {
44 		i = (0x000fffff)>>j0;
45 		if(((i0&i)|i1)==0) return x; /* x is integral */
46 		if(huge+x>0.0) {	/* raise inexact flag */
47 		    if(i0<0) i0 += (0x00100000)>>j0;
48 		    i0 &= (~i); i1=0;
49 		}
50 	    }
51 	} else if (j0>51) {
52 	    if(j0==0x400) return x+x;	/* inf or NaN */
53 	    else return x;		/* x is integral */
54 	} else {
55 	    i = ((u_int32_t)(0xffffffff))>>(j0-20);
56 	    if((i1&i)==0) return x;	/* x is integral */
57 	    if(huge+x>0.0) { 		/* raise inexact flag */
58 		if(i0<0) {
59 		    if(j0==20) i0+=1;
60 		    else {
61 			j = i1+(1<<(52-j0));
62 			if(j<i1) i0 +=1 ; 	/* got a carry */
63 			i1=j;
64 		    }
65 		}
66 		i1 &= (~i);
67 	    }
68 	}
69 	INSERT_WORDS(x,i0,i1);
70 	return x;
71 }
72 
73 #if LDBL_MANT_DIG == 53
74 __weak_reference(floor, floorl);
75 #endif
76