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s_modf.c
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1 
2 /* @(#)s_modf.c 1.3 95/01/18 */
3 /*
4  * ====================================================
5  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6  *
7  * Developed at SunSoft, a Sun Microsystems, Inc. business.
8  * Permission to use, copy, modify, and distribute this
9  * software is freely granted, provided that this notice
10  * is preserved.
11  * ====================================================
12  */
13 
14 /*
15  * modf(double x, double *iptr)
16  * return fraction part of x, and return x's integral part in *iptr.
17  * Method:
18  * Bit twiddling.
19  *
20  * Exception:
21  * No exception.
22  */
23 
24 #include "fdlibm.h"
25 
26 #ifdef __STDC__
27 static const double one = 1.0;
28 #else
29 static double one = 1.0;
30 #endif
31 
32 #ifdef __STDC__
33  double modf(double x, double *iptr)
34 #else
35  double modf(x, iptr)
36  double x,*iptr;
37 #endif
38 {
39  int i0,i1,j0;
40  unsigned i;
41  i0 = __HI(x); /* high x */
42  i1 = __LO(x); /* low x */
43  j0 = ((i0>>20)&0x7ff)-0x3ff; /* exponent of x */
44  if(j0<20) { /* integer part in high x */
45  if(j0<0) { /* |x|<1 */
46  __HIp(iptr) = i0&0x80000000;
47  __LOp(iptr) = 0; /* *iptr = +-0 */
48  return x;
49  } else {
50  i = (0x000fffff)>>j0;
51  if(((i0&i)|i1)==0) { /* x is integral */
52  *iptr = x;
53  __HI(x) &= 0x80000000;
54  __LO(x) = 0; /* return +-0 */
55  return x;
56  } else {
57  __HIp(iptr) = i0&(~i);
58  __LOp(iptr) = 0;
59  return x - *iptr;
60  }
61  }
62  } else if (j0>51) { /* no fraction part */
63  *iptr = x*one;
64  __HI(x) &= 0x80000000;
65  __LO(x) = 0; /* return +-0 */
66  return x;
67  } else { /* fraction part in low x */
68  i = ((unsigned)(0xffffffff))>>(j0-20);
69  if((i1&i)==0) { /* x is integral */
70  *iptr = x;
71  __HI(x) &= 0x80000000;
72  __LO(x) = 0; /* return +-0 */
73  return x;
74  } else {
75  __HIp(iptr) = i0;
76  __LOp(iptr) = i1&(~i);
77  return x - *iptr;
78  }
79  }
80 }