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#include <sys/cdefs.h>
14__FBSDID("$FreeBSD$");
15
16/*
17 * modf(double x, double *iptr)
18 * return fraction part of x, and return x's integral part in *iptr.
19 * Method:
20 *	Bit twiddling.
21 *
22 * Exception:
23 *	No exception.
24 */
25
26#include <sys/types.h>
27#include <machine/endian.h>
28#include <math.h>
29
30/* Bit fiddling routines copied from msun/src/math_private.h,v 1.15 */
31
32#if BYTE_ORDER == BIG_ENDIAN
33
34typedef union
35{
36  double value;
37  struct
38  {
39    u_int32_t msw;
40    u_int32_t lsw;
41  } parts;
42} ieee_double_shape_type;
43
44#endif
45
46#if BYTE_ORDER == LITTLE_ENDIAN
47
48typedef union
49{
50  double value;
51  struct
52  {
53    u_int32_t lsw;
54    u_int32_t msw;
55  } parts;
56} ieee_double_shape_type;
57
58#endif
59
60/* Get two 32 bit ints from a double.  */
61
62#define EXTRACT_WORDS(ix0,ix1,d)				\
63do {								\
64  ieee_double_shape_type ew_u;					\
65  ew_u.value = (d);						\
66  (ix0) = ew_u.parts.msw;					\
67  (ix1) = ew_u.parts.lsw;					\
68} while (0)
69
70/* Get the more significant 32 bit int from a double.  */
71
72#define GET_HIGH_WORD(i,d)					\
73do {								\
74  ieee_double_shape_type gh_u;					\
75  gh_u.value = (d);						\
76  (i) = gh_u.parts.msw;						\
77} while (0)
78
79/* Set a double from two 32 bit ints.  */
80
81#define INSERT_WORDS(d,ix0,ix1)					\
82do {								\
83  ieee_double_shape_type iw_u;					\
84  iw_u.parts.msw = (ix0);					\
85  iw_u.parts.lsw = (ix1);					\
86  (d) = iw_u.value;						\
87} while (0)
88
89static const double one = 1.0;
90
91double
92modf(double x, double *iptr)
93{
94	int32_t i0,i1,j0;
95	u_int32_t i;
96	EXTRACT_WORDS(i0,i1,x);
97	j0 = ((i0>>20)&0x7ff)-0x3ff;	/* exponent of x */
98	if(j0<20) {			/* integer part in high x */
99	    if(j0<0) {			/* |x|<1 */
100	        INSERT_WORDS(*iptr,i0&0x80000000,0);	/* *iptr = +-0 */
101		return x;
102	    } else {
103		i = (0x000fffff)>>j0;
104		if(((i0&i)|i1)==0) {		/* x is integral */
105		    u_int32_t high;
106		    *iptr = x;
107		    GET_HIGH_WORD(high,x);
108		    INSERT_WORDS(x,high&0x80000000,0);	/* return +-0 */
109		    return x;
110		} else {
111		    INSERT_WORDS(*iptr,i0&(~i),0);
112		    return x - *iptr;
113		}
114	    }
115	} else if (j0>51) {		/* no fraction part */
116	    u_int32_t high;
117	    if (j0 == 0x400) {		/* inf/NaN */
118		*iptr = x;
119		return 0.0 / x;
120	    }
121	    *iptr = x*one;
122	    GET_HIGH_WORD(high,x);
123	    INSERT_WORDS(x,high&0x80000000,0);	/* return +-0 */
124	    return x;
125	} else {			/* fraction part in low x */
126	    i = ((u_int32_t)(0xffffffff))>>(j0-20);
127	    if((i1&i)==0) { 		/* x is integral */
128	        u_int32_t high;
129		*iptr = x;
130		GET_HIGH_WORD(high,x);
131		INSERT_WORDS(x,high&0x80000000,0);	/* return +-0 */
132		return x;
133	    } else {
134	        INSERT_WORDS(*iptr,i0,i1&(~i));
135		return x - *iptr;
136	    }
137	}
138}
139