1 /*
2 * ====================================================
3 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
4 *
5 * Developed at SunPro, a Sun Microsystems, Inc. business.
6 * Permission to use, copy, modify, and distribute this
7 * software is freely granted, provided that this notice
8 * is preserved.
9 * ====================================================
10 */
11
12 /*
13 * rint(x)
14 * Return x rounded to integral value according to the prevailing
15 * rounding mode.
16 * Method:
17 * Using floating addition.
18 * Exception:
19 * Inexact flag raised if x not equal to rint(x).
20 */
21
22 #include "math.h"
23 #include "math_private.h"
24
25 static const double
26 TWO52[2]={
27 4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
28 -4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
29 };
30
rint(double x)31 double rint(double x)
32 {
33 int32_t i0, _j0, sx;
34 u_int32_t i,i1;
35 double t;
36 /* We use w = x + 2^52; t = w - 2^52; trick to round x to integer.
37 * This trick requires that compiler does not optimize it
38 * by keeping intermediate result w in a register wider than double.
39 * Declaring w volatile assures that value gets truncated to double
40 * (unfortunately, it also forces store+load):
41 */
42 volatile double w;
43
44 EXTRACT_WORDS(i0,i1,x);
45 /* Unbiased exponent */
46 _j0 = ((((u_int32_t)i0) >> 20)&0x7ff)-0x3ff;
47
48 if (_j0 > 51) {
49 //Why bother? Just returning x works too
50 //if (_j0 == 0x400) /* inf or NaN */
51 // return x+x;
52 return x; /* x is integral */
53 }
54
55 /* Sign */
56 sx = ((u_int32_t)i0) >> 31;
57
58 if (_j0<20) {
59 if (_j0<0) { /* |x| < 1 */
60 if (((i0&0x7fffffff)|i1)==0) return x;
61 i1 |= (i0&0x0fffff);
62 i0 &= 0xfffe0000;
63 i0 |= ((i1|-i1)>>12)&0x80000;
64 SET_HIGH_WORD(x,i0);
65 w = TWO52[sx]+x;
66 t = w-TWO52[sx];
67 GET_HIGH_WORD(i0,t);
68 SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
69 return t;
70 } else {
71 i = (0x000fffff)>>_j0;
72 if (((i0&i)|i1)==0) return x; /* x is integral */
73 i>>=1;
74 if (((i0&i)|i1)!=0) {
75 if (_j0==19) i1 = 0x40000000;
76 else i0 = (i0&(~i))|((0x20000)>>_j0);
77 }
78 }
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 w = TWO52[sx]+x;
87 return w-TWO52[sx];
88 }
89 libm_hidden_def(rint)
90
91 strong_alias(rint, nearbyint)
92 libm_hidden_def(nearbyint)
93