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.h"
29 #include "math_private.h"
30
31 static const double
32 TWO52[2]={
33 4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
34 -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
35 };
36
37 double
rint(double x)38 rint(double x)
39 {
40 int32_t i0,j0,sx;
41 u_int32_t i,i1;
42 double w,t;
43 EXTRACT_WORDS(i0,i1,x);
44 sx = (i0>>31)&1;
45 j0 = ((i0>>20)&0x7ff)-0x3ff;
46 if(j0<20) {
47 if(j0<0) {
48 if(((i0&0x7fffffff)|i1)==0) return x;
49 i1 |= (i0&0x0fffff);
50 i0 &= 0xfffe0000;
51 i0 |= ((i1|-i1)>>12)&0x80000;
52 SET_HIGH_WORD(x,i0);
53 STRICT_ASSIGN(double,w,TWO52[sx]+x);
54 t = w-TWO52[sx];
55 GET_HIGH_WORD(i0,t);
56 SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
57 return t;
58 } else {
59 i = (0x000fffff)>>j0;
60 if(((i0&i)|i1)==0) return x; /* x is integral */
61 i>>=1;
62 if(((i0&i)|i1)!=0) {
63 /*
64 * Some bit is set after the 0.5 bit. To avoid the
65 * possibility of errors from double rounding in
66 * w = TWO52[sx]+x, adjust the 0.25 bit to a lower
67 * guard bit. We do this for all j0<=51. The
68 * adjustment is trickiest for j0==18 and j0==19
69 * since then it spans the word boundary.
70 */
71 if(j0==19) i1 = 0x40000000; else
72 if(j0==18) i1 = 0x80000000; else
73 i0 = (i0&(~i))|((0x20000)>>j0);
74 }
75 }
76 } else if (j0>51) {
77 if(j0==0x400) return x+x; /* inf or NaN */
78 else return x; /* x is integral */
79 } else {
80 i = ((u_int32_t)(0xffffffff))>>(j0-20);
81 if((i1&i)==0) return x; /* x is integral */
82 i>>=1;
83 if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
84 }
85 INSERT_WORDS(x,i0,i1);
86 STRICT_ASSIGN(double,w,TWO52[sx]+x);
87 return w-TWO52[sx];
88 }
89
90 #if (LDBL_MANT_DIG == 53)
91 __weak_reference(rint, rintl);
92 #endif
93