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---
s_rint.c (1953B)
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1 /* @(#)s_rint.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 #ifndef lint
14 static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_rint.c,v 1.10 2003/07/23 04:53:46 peter Exp $";
15 #endif
16
17 /*
18 * rint(x)
19 * Return x rounded to integral value according to the prevailing
20 * rounding mode.
21 * Method:
22 * Using floating addition.
23 * Exception:
24 * Inexact flag raised if x not equal to rint(x).
25 */
26
27 #include "math.h"
28 #include "math_private.h"
29
30 static const double
31 TWO52[2]={
32 4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
33 -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
34 };
35
36 double
37 rint(double x)
38 {
39 int32_t i0,j0,sx;
40 u_int32_t i,i1;
41 double w,t;
42 EXTRACT_WORDS(i0,i1,x);
43 sx = (i0>>31)&1;
44 j0 = ((i0>>20)&0x7ff)-0x3ff;
45 if(j0<20) {
46 if(j0<0) {
47 if(((i0&0x7fffffff)|i1)==0) return x;
48 i1 |= (i0&0x0fffff);
49 i0 &= 0xfffe0000;
50 i0 |= ((i1|-i1)>>12)&0x80000;
51 SET_HIGH_WORD(x,i0);
52 w = TWO52[sx]+x;
53 t = w-TWO52[sx];
54 GET_HIGH_WORD(i0,t);
55 SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
56 return t;
57 } else {
58 i = (0x000fffff)>>j0;
59 if(((i0&i)|i1)==0) return x; /* x is integral */
60 i>>=1;
61 if(((i0&i)|i1)!=0) {
62 if(j0==19) i1 = 0x40000000; else
63 i0 = (i0&(~i))|((0x20000)>>j0);
64 }
65 }
66 } else if (j0>51) {
67 if(j0==0x400) return x+x; /* inf or NaN */
68 else return x; /* x is integral */
69 } else {
70 i = ((u_int32_t)(0xffffffff))>>(j0-20);
71 if((i1&i)==0) return x; /* x is integral */
72 i>>=1;
73 if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
74 }
75 INSERT_WORDS(x,i0,i1);
76 w = TWO52[sx]+x;
77 return w-TWO52[sx];
78 }