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