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
14static 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
30static const double one = 1.0;
31
32double
33modf(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