1 /* @(#)s_scalbn.c 5.1 93/09/24 */
2 /* @(#)fdlibm.h 5.1 93/09/24 */
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 #include <sys/cdefs.h>
15 __FBSDID("$FreeBSD$");
16
17 #include <sys/types.h>
18 #include <machine/endian.h>
19 #include <math.h>
20
21 /* Bit fiddling routines copied from msun/src/math_private.h,v 1.15 */
22
23 #if BYTE_ORDER == BIG_ENDIAN
24
25 typedef union
26 {
27 double value;
28 struct
29 {
30 u_int32_t msw;
31 u_int32_t lsw;
32 } parts;
33 } ieee_double_shape_type;
34
35 #endif
36
37 #if BYTE_ORDER == LITTLE_ENDIAN
38
39 typedef union
40 {
41 double value;
42 struct
43 {
44 u_int32_t lsw;
45 u_int32_t msw;
46 } parts;
47 } ieee_double_shape_type;
48
49 #endif
50
51 /* Get two 32 bit ints from a double. */
52
53 #define EXTRACT_WORDS(ix0,ix1,d) \
54 do { \
55 ieee_double_shape_type ew_u; \
56 ew_u.value = (d); \
57 (ix0) = ew_u.parts.msw; \
58 (ix1) = ew_u.parts.lsw; \
59 } while (0)
60
61 /* Get the more significant 32 bit int from a double. */
62
63 #define GET_HIGH_WORD(i,d) \
64 do { \
65 ieee_double_shape_type gh_u; \
66 gh_u.value = (d); \
67 (i) = gh_u.parts.msw; \
68 } while (0)
69
70 /* Set the more significant 32 bits of a double from an int. */
71
72 #define SET_HIGH_WORD(d,v) \
73 do { \
74 ieee_double_shape_type sh_u; \
75 sh_u.value = (d); \
76 sh_u.parts.msw = (v); \
77 (d) = sh_u.value; \
78 } while (0)
79
80
81 static const double
82 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
83 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
84 huge = 1.0e+300,
85 tiny = 1.0e-300;
86
87 static double
_copysign(double x,double y)88 _copysign(double x, double y)
89 {
90 u_int32_t hx,hy;
91 GET_HIGH_WORD(hx,x);
92 GET_HIGH_WORD(hy,y);
93 SET_HIGH_WORD(x,(hx&0x7fffffff)|(hy&0x80000000));
94 return x;
95 }
96
97 double
ldexp(double x,int n)98 ldexp(double x, int n)
99 {
100 int32_t k,hx,lx;
101 EXTRACT_WORDS(hx,lx,x);
102 k = (hx&0x7ff00000)>>20; /* extract exponent */
103 if (k==0) { /* 0 or subnormal x */
104 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
105 x *= two54;
106 GET_HIGH_WORD(hx,x);
107 k = ((hx&0x7ff00000)>>20) - 54;
108 if (n< -50000) return tiny*x; /*underflow*/
109 }
110 if (k==0x7ff) return x+x; /* NaN or Inf */
111 k = k+n;
112 if (k > 0x7fe) return huge*_copysign(huge,x); /* overflow */
113 if (k > 0) /* normal result */
114 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
115 if (k <= -54) {
116 if (n > 50000) /* in case integer overflow in n+k */
117 return huge*_copysign(huge,x); /*overflow*/
118 else return tiny*_copysign(tiny,x); /*underflow*/
119 }
120 k += 54; /* subnormal result */
121 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
122 return x*twom54;
123 }
124