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
floor(double x)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