1 /* @(#)s_modf.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 #ifndef lint
14 static char rcsid[] = "$FreeBSD$";
15 #endif
16
17 /*
18 * modf(double x, double *iptr)
19 * return fraction part of x, and return x's integral part in *iptr.
20 * Method:
21 * Bit twiddling.
22 *
23 * Exception:
24 * No exception.
25 */
26
27 #include "math.h"
28 #include "math_private.h"
29
30 static const double one = 1.0;
31
32 double
modf(double x,double * iptr)33 modf(double x, double *iptr)
34 {
35 int32_t i0,i1,j0;
36 u_int32_t i;
37 EXTRACT_WORDS(i0,i1,x);
38 j0 = ((i0>>20)&0x7ff)-0x3ff; /* exponent of x */
39 if(j0<20) { /* integer part in high x */
40 if(j0<0) { /* |x|<1 */
41 INSERT_WORDS(*iptr,i0&0x80000000,0); /* *iptr = +-0 */
42 return x;
43 } else {
44 i = (0x000fffff)>>j0;
45 if(((i0&i)|i1)==0) { /* x is integral */
46 u_int32_t high;
47 *iptr = x;
48 GET_HIGH_WORD(high,x);
49 INSERT_WORDS(x,high&0x80000000,0); /* return +-0 */
50 return x;
51 } else {
52 INSERT_WORDS(*iptr,i0&(~i),0);
53 return x - *iptr;
54 }
55 }
56 } else if (j0>51) { /* no fraction part */
57 u_int32_t high;
58 if (j0 == 0x400) { /* inf/NaN */
59 *iptr = x;
60 return 0.0 / x;
61 }
62 *iptr = x*one;
63 GET_HIGH_WORD(high,x);
64 INSERT_WORDS(x,high&0x80000000,0); /* return +-0 */
65 return x;
66 } else { /* fraction part in low x */
67 i = ((u_int32_t)(0xffffffff))>>(j0-20);
68 if((i1&i)==0) { /* x is integral */
69 u_int32_t high;
70 *iptr = x;
71 GET_HIGH_WORD(high,x);
72 INSERT_WORDS(x,high&0x80000000,0); /* return +-0 */
73 return x;
74 } else {
75 INSERT_WORDS(*iptr,i0,i1&(~i));
76 return x - *iptr;
77 }
78 }
79 }
80