1 /* @(#)s_scalbn.c 5.1 93/09/24 */
2 /* @(#)fdlibm.h 5.1 93/09/24 */
3 /* $FreeBSD: head/lib/libc/gen/ldexp.c 140607 2005-01-22 06:03:40Z das $ */
4 /*
5 * ====================================================
6 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
7 *
8 * Developed at SunPro, a Sun Microsystems, Inc. business.
9 * Permission to use, copy, modify, and distribute this
10 * software is freely granted, provided that this notice
11 * is preserved.
12 * ====================================================
13 */
14
15 #include <sys/types.h>
16 #include <machine/endian.h>
17 #include <math.h>
18
19 /* Bit fiddling routines copied from msun/src/math_private.h,v 1.15 */
20
21 #if BYTE_ORDER == BIG_ENDIAN
22
23 typedef union
24 {
25 double value;
26 struct
27 {
28 u_int32_t msw;
29 u_int32_t lsw;
30 } parts;
31 } ieee_double_shape_type;
32
33 #endif
34
35 #if BYTE_ORDER == LITTLE_ENDIAN
36
37 typedef union
38 {
39 double value;
40 struct
41 {
42 u_int32_t lsw;
43 u_int32_t msw;
44 } parts;
45 } ieee_double_shape_type;
46
47 #endif
48
49 /* Get two 32 bit ints from a double. */
50
51 #define EXTRACT_WORDS(ix0,ix1,d) \
52 do { \
53 ieee_double_shape_type ew_u; \
54 ew_u.value = (d); \
55 (ix0) = ew_u.parts.msw; \
56 (ix1) = ew_u.parts.lsw; \
57 } while (0)
58
59 /* Get the more significant 32 bit int from a double. */
60
61 #define GET_HIGH_WORD(i,d) \
62 do { \
63 ieee_double_shape_type gh_u; \
64 gh_u.value = (d); \
65 (i) = gh_u.parts.msw; \
66 } while (0)
67
68 /* Set the more significant 32 bits of a double from an int. */
69
70 #define SET_HIGH_WORD(d,v) \
71 do { \
72 ieee_double_shape_type sh_u; \
73 sh_u.value = (d); \
74 sh_u.parts.msw = (v); \
75 (d) = sh_u.value; \
76 } while (0)
77
78
79 static const double
80 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
81 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
82 huge = 1.0e+300,
83 tiny = 1.0e-300;
84
85 static double
_copysign(double x,double y)86 _copysign(double x, double y)
87 {
88 u_int32_t hx,hy;
89 GET_HIGH_WORD(hx,x);
90 GET_HIGH_WORD(hy,y);
91 SET_HIGH_WORD(x,(hx&0x7fffffff)|(hy&0x80000000));
92 return x;
93 }
94
95 double
ldexp(double x,int n)96 ldexp(double x, int n)
97 {
98 int32_t k,hx,lx;
99 EXTRACT_WORDS(hx,lx,x);
100 k = (hx&0x7ff00000)>>20; /* extract exponent */
101 if (k==0) { /* 0 or subnormal x */
102 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
103 x *= two54;
104 GET_HIGH_WORD(hx,x);
105 k = ((hx&0x7ff00000)>>20) - 54;
106 if (n< -50000) return tiny*x; /*underflow*/
107 }
108 if (k==0x7ff) return x+x; /* NaN or Inf */
109 k = k+n;
110 if (k > 0x7fe) return huge*_copysign(huge,x); /* overflow */
111 if (k > 0) /* normal result */
112 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
113 if (k <= -54) {
114 if (n > 50000) /* in case integer overflow in n+k */
115 return huge*_copysign(huge,x); /*overflow*/
116 else return tiny*_copysign(tiny,x); /*underflow*/
117 }
118 k += 54; /* subnormal result */
119 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
120 return x*twom54;
121 }
122