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
34 typedef 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
48 typedef 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) \
63 do { \
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) \
73 do { \
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) \
82 do { \
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
89 static const double one = 1.0;
90
91 double
modf(double x,double * iptr)92 modf(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