1 /*
2  * Copyright (c) 1998, 2001, Oracle and/or its affiliates. All rights reserved.
3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4  *
5  * This code is free software; you can redistribute it and/or modify it
6  * under the terms of the GNU General Public License version 2 only, as
7  * published by the Free Software Foundation.  Oracle designates this
8  * particular file as subject to the "Classpath" exception as provided
9  * by Oracle in the LICENSE file that accompanied this code.
10  *
11  * This code is distributed in the hope that it will be useful, but WITHOUT
12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14  * version 2 for more details (a copy is included in the LICENSE file that
15  * accompanied this code).
16  *
17  * You should have received a copy of the GNU General Public License version
18  * 2 along with this work; if not, write to the Free Software Foundation,
19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20  *
21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22  * or visit www.oracle.com if you need additional information or have any
23  * questions.
24  */
25 
26 /* __ieee754_remainder(x,p)
27  * Return :
28  *      returns  x REM p  =  x - [x/p]*p as if in infinite
29  *      precise arithmetic, where [x/p] is the (infinite bit)
30  *      integer nearest x/p (in half way case choose the even one).
31  * Method :
32  *      Based on fmod() return x-[x/p]chopped*p exactlp.
33  */
34 
35 #include "fdlibm.h"
36 
37 #ifdef __STDC__
38 static const double zero = 0.0;
39 #else
40 static double zero = 0.0;
41 #endif
42 
43 
44 #ifdef __STDC__
__ieee754_remainder(double x,double p)45         double __ieee754_remainder(double x, double p)
46 #else
47         double __ieee754_remainder(x,p)
48         double x,p;
49 #endif
50 {
51         int hx,hp;
52         unsigned sx,lx,lp;
53         double p_half;
54 
55         hx = __HI(x);           /* high word of x */
56         lx = __LO(x);           /* low  word of x */
57         hp = __HI(p);           /* high word of p */
58         lp = __LO(p);           /* low  word of p */
59         sx = hx&0x80000000;
60         hp &= 0x7fffffff;
61         hx &= 0x7fffffff;
62 
63     /* purge off exception values */
64         if((hp|lp)==0) return (x*p)/(x*p);      /* p = 0 */
65         if((hx>=0x7ff00000)||                   /* x not finite */
66           ((hp>=0x7ff00000)&&                   /* p is NaN */
67           (((hp-0x7ff00000)|lp)!=0)))
68             return (x*p)/(x*p);
69 
70 
71         if (hp<=0x7fdfffff) x = __ieee754_fmod(x,p+p);  /* now x < 2p */
72         if (((hx-hp)|(lx-lp))==0) return zero*x;
73         x  = fabs(x);
74         p  = fabs(p);
75         if (hp<0x00200000) {
76             if(x+x>p) {
77                 x-=p;
78                 if(x+x>=p) x -= p;
79             }
80         } else {
81             p_half = 0.5*p;
82             if(x>p_half) {
83                 x-=p;
84                 if(x>=p_half) x -= p;
85             }
86         }
87         __HI(x) ^= sx;
88         return x;
89 }
90