s_modf.c revision 2117 
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[] = "$Id: s_modf.c,v 1.6 1994/08/18 23:07:09 jtc Exp $";
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#ifdef __STDC__
31static const double one = 1.0;
32#else
33static double one = 1.0;
34#endif
35
36#ifdef __STDC__
37	double modf(double x, double *iptr)
38#else
39	double modf(x, iptr)
40	double x,*iptr;
41#endif
42{
43	int32_t i0,i1,j0;
44	u_int32_t i;
45	EXTRACT_WORDS(i0,i1,x);
46	j0 = ((i0>>20)&0x7ff)-0x3ff;	/* exponent of x */
47	if(j0<20) {			/* integer part in high x */
48	    if(j0<0) {			/* |x|<1 */
49	        INSERT_WORDS(*iptr,i0&0x80000000,0);	/* *iptr = +-0 */
50		return x;
51	    } else {
52		i = (0x000fffff)>>j0;
53		if(((i0&i)|i1)==0) {		/* x is integral */
54		    u_int32_t high;
55		    *iptr = x;
56		    GET_HIGH_WORD(high,x);
57		    INSERT_WORDS(x,high&0x80000000,0);	/* return +-0 */
58		    return x;
59		} else {
60		    INSERT_WORDS(*iptr,i0&(~i),0);
61		    return x - *iptr;
62		}
63	    }
64	} else if (j0>51) {		/* no fraction part */
65	    u_int32_t high;
66	    *iptr = x*one;
67	    GET_HIGH_WORD(high,x);
68	    INSERT_WORDS(x,high&0x80000000,0);	/* return +-0 */
69	    return x;
70	} else {			/* fraction part in low x */
71	    i = ((u_int32_t)(0xffffffff))>>(j0-20);
72	    if((i1&i)==0) { 		/* x is integral */
73	        u_int32_t high;
74		*iptr = x;
75		GET_HIGH_WORD(high,x);
76		INSERT_WORDS(x,high&0x80000000,0);	/* return +-0 */
77		return x;
78	    } else {
79	        INSERT_WORDS(*iptr,i0,i1&(~i));
80		return x - *iptr;
81	    }
82	}
83}
84