1 /* @(#)s_modf.c 5.1 93/09/24 */
2 /* $FreeBSD: head/lib/libc/gen/modf.c 226606 2011-10-21 06:40:36Z das $ */
3 /*
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6 *
7 * Developed at SunPro, a Sun Microsystems, Inc. business.
8 * Permission to use, copy, modify, and distribute this
9 * software is freely granted, provided that this notice
10 * is preserved.
11 * ====================================================
12 */
13
14 /*
15 * modf(double x, double *iptr)
16 * return fraction part of x, and return x's integral part in *iptr.
17 * Method:
18 * Bit twiddling.
19 *
20 * Exception:
21 * No exception.
22 */
23
24 #include <sys/types.h>
25 #include <machine/endian.h>
26 #include <math.h>
27
28 /* Bit fiddling routines copied from msun/src/math_private.h,v 1.15 */
29
30 #if BYTE_ORDER == BIG_ENDIAN
31
32 typedef union
33 {
34 double value;
35 struct
36 {
37 u_int32_t msw;
38 u_int32_t lsw;
39 } parts;
40 } ieee_double_shape_type;
41
42 #endif
43
44 #if BYTE_ORDER == LITTLE_ENDIAN
45
46 typedef union
47 {
48 double value;
49 struct
50 {
51 u_int32_t lsw;
52 u_int32_t msw;
53 } parts;
54 } ieee_double_shape_type;
55
56 #endif
57
58 /* Get two 32 bit ints from a double. */
59
60 #define EXTRACT_WORDS(ix0,ix1,d) \
61 do { \
62 ieee_double_shape_type ew_u; \
63 ew_u.value = (d); \
64 (ix0) = ew_u.parts.msw; \
65 (ix1) = ew_u.parts.lsw; \
66 } while (0)
67
68 /* Get the more significant 32 bit int from a double. */
69
70 #define GET_HIGH_WORD(i,d) \
71 do { \
72 ieee_double_shape_type gh_u; \
73 gh_u.value = (d); \
74 (i) = gh_u.parts.msw; \
75 } while (0)
76
77 /* Set a double from two 32 bit ints. */
78
79 #define INSERT_WORDS(d,ix0,ix1) \
80 do { \
81 ieee_double_shape_type iw_u; \
82 iw_u.parts.msw = (ix0); \
83 iw_u.parts.lsw = (ix1); \
84 (d) = iw_u.value; \
85 } while (0)
86
87 static const double one = 1.0;
88
89 double
modf(double x,double * iptr)90 modf(double x, double *iptr)
91 {
92 int32_t i0,i1,j0;
93 u_int32_t i;
94 EXTRACT_WORDS(i0,i1,x);
95 j0 = ((i0>>20)&0x7ff)-0x3ff; /* exponent of x */
96 if(j0<20) { /* integer part in high x */
97 if(j0<0) { /* |x|<1 */
98 INSERT_WORDS(*iptr,i0&0x80000000,0); /* *iptr = +-0 */
99 return x;
100 } else {
101 i = (0x000fffff)>>j0;
102 if(((i0&i)|i1)==0) { /* x is integral */
103 u_int32_t high;
104 *iptr = x;
105 GET_HIGH_WORD(high,x);
106 INSERT_WORDS(x,high&0x80000000,0); /* return +-0 */
107 return x;
108 } else {
109 INSERT_WORDS(*iptr,i0&(~i),0);
110 return x - *iptr;
111 }
112 }
113 } else if (j0>51) { /* no fraction part */
114 u_int32_t high;
115 if (j0 == 0x400) { /* inf/NaN */
116 *iptr = x;
117 return 0.0 / x;
118 }
119 *iptr = x*one;
120 GET_HIGH_WORD(high,x);
121 INSERT_WORDS(x,high&0x80000000,0); /* return +-0 */
122 return x;
123 } else { /* fraction part in low x */
124 i = ((u_int32_t)(0xffffffff))>>(j0-20);
125 if((i1&i)==0) { /* x is integral */
126 u_int32_t high;
127 *iptr = x;
128 GET_HIGH_WORD(high,x);
129 INSERT_WORDS(x,high&0x80000000,0); /* return +-0 */
130 return x;
131 } else {
132 INSERT_WORDS(*iptr,i0,i1&(~i));
133 return x - *iptr;
134 }
135 }
136 }
137