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 #include <math.h>
25
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,jj0,sx;
38 u_int32_t i,i1;
39 double t;
40 volatile double w; /* clip extra precision */
41 EXTRACT_WORDS(i0,i1,x);
42 sx = (i0>>31)&1;
43 jj0 = ((i0>>20)&0x7ff)-0x3ff;
44 if(jj0<20) {
45 if(jj0<0) {
46 if(((i0&0x7fffffff)|i1)==0) return x;
47 i1 |= (i0&0x0fffff);
48 i0 &= 0xfffe0000;
49 i0 |= ((i1|-i1)>>12)&0x80000;
50 SET_HIGH_WORD(x,i0);
51 w = TWO52[sx]+x;
52 t = w-TWO52[sx];
53 GET_HIGH_WORD(i0,t);
54 SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
55 return t;
56 } else {
57 i = (0x000fffff)>>jj0;
58 if(((i0&i)|i1)==0) return x; /* x is integral */
59 i>>=1;
60 if(((i0&i)|i1)!=0) {
61 if(jj0==19) i1 = 0x40000000; else
62 i0 = (i0&(~i))|((0x20000)>>jj0);
63 }
64 }
65 } else if (jj0>51) {
66 if(jj0==0x400) return x+x; /* inf or NaN */
67 else return x; /* x is integral */
68 } else {
69 i = ((u_int32_t)(0xffffffff))>>(jj0-20);
70 if((i1&i)==0) return x; /* x is integral */
71 i>>=1;
72 if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(jj0-20));
73 }
74 INSERT_WORDS(x,i0,i1);
75 w = TWO52[sx]+x;
76 return w-TWO52[sx];
77 }
78
79 #if LDBL_MANT_DIG == DBL_MANT_DIG
80 __strong_alias(rintl, rint);
81 #endif /* LDBL_MANT_DIG == DBL_MANT_DIG */
82