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