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 /*
14 * rint(x)
15 * Return x rounded to integral value according to the prevailing
16 * rounding mode.
17 * Method:
18 * Using floating addition.
19 * Exception:
20 * Inexact flag raised if x not equal to rint(x).
21 */
22
23 #include <float.h>
24
25 #include "math.h"
26 #include "math_private.h"
27
28 static const double
29 TWO52[2]={
30 4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
31 -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
32 };
33
34 double
rint(double x)35 rint(double x)
36 {
37 int32_t i0,j0,sx;
38 u_int32_t i,i1;
39 double w,t;
40 EXTRACT_WORDS(i0,i1,x);
41 sx = (i0>>31)&1;
42 j0 = ((i0>>20)&0x7ff)-0x3ff;
43 if(j0<20) {
44 if(j0<0) {
45 if(((i0&0x7fffffff)|i1)==0) return x;
46 i1 |= (i0&0x0fffff);
47 i0 &= 0xfffe0000;
48 i0 |= ((i1|-i1)>>12)&0x80000;
49 SET_HIGH_WORD(x,i0);
50 STRICT_ASSIGN(double,w,TWO52[sx]+x);
51 t = w-TWO52[sx];
52 GET_HIGH_WORD(i0,t);
53 SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
54 return t;
55 } else {
56 i = (0x000fffff)>>j0;
57 if(((i0&i)|i1)==0) return x; /* x is integral */
58 i>>=1;
59 if(((i0&i)|i1)!=0) {
60 /*
61 * Some bit is set after the 0.5 bit. To avoid the
62 * possibility of errors from double rounding in
63 * w = TWO52[sx]+x, adjust the 0.25 bit to a lower
64 * guard bit. We do this for all j0<=51. The
65 * adjustment is trickiest for j0==18 and j0==19
66 * since then it spans the word boundary.
67 */
68 if(j0==19) i1 = 0x40000000; else
69 if(j0==18) i1 = 0x80000000; else
70 i0 = (i0&(~i))|((0x20000)>>j0);
71 }
72 }
73 } else if (j0>51) {
74 if(j0==0x400) return x+x; /* inf or NaN */
75 else return x; /* x is integral */
76 } else {
77 i = ((u_int32_t)(0xffffffff))>>(j0-20);
78 if((i1&i)==0) return x; /* x is integral */
79 i>>=1;
80 if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
81 }
82 INSERT_WORDS(x,i0,i1);
83 STRICT_ASSIGN(double,w,TWO52[sx]+x);
84 return w-TWO52[sx];
85 }
86
87 #if (LDBL_MANT_DIG == 53)
88 __weak_reference(rint, rintl);
89 #endif
90