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 //#include <sys/cdefs.h>
14 //__FBSDID("$FreeBSD$");
15
16 /*
17 * rint(x)
18 * Return x rounded to integral value according to the prevailing
19 * rounding mode.
20 * Method:
21 * Using floating addition.
22 * Exception:
23 * Inexact flag raised if x not equal to rint(x).
24 */
25
26 #include <float.h>
27
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
rint(double x)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 STRICT_ASSIGN(double,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 /*
63 * Some bit is set after the 0.5 bit. To avoid the
64 * possibility of errors from double rounding in
65 * w = TWO52[sx]+x, adjust the 0.25 bit to a lower
66 * guard bit. We do this for all j0<=51. The
67 * adjustment is trickiest for j0==18 and j0==19
68 * since then it spans the word boundary.
69 */
70 if(j0==19) i1 = 0x40000000; else
71 if(j0==18) i1 = 0x80000000; else
72 i0 = (i0&(~i))|((0x20000)>>j0);
73 }
74 }
75 } else if (j0>51) {
76 if(j0==0x400) return x+x; /* inf or NaN */
77 else return x; /* x is integral */
78 } else {
79 i = ((u_int32_t)(0xffffffff))>>(j0-20);
80 if((i1&i)==0) return x; /* x is integral */
81 i>>=1;
82 if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
83 }
84 INSERT_WORDS(x,i0,i1);
85 STRICT_ASSIGN(double,w,TWO52[sx]+x);
86 return w-TWO52[sx];
87 }
88