1 /* $OpenBSD: ldexp.c,v 1.10 2015/10/27 05:54:49 guenther Exp $ */
2 /* @(#)s_scalbn.c 5.1 93/09/24 */
3 /* @(#)fdlibm.h 5.1 93/09/24 */
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 <endian.h>
17 #include <float.h>
18 #include <math.h>
19
20 /* Bit fiddling routines copied from msun/src/math_private.h,v 1.15 */
21
22 #if (BYTE_ORDER == BIG_ENDIAN) || (defined(__arm__) && !defined(__VFP_FP__))
23
24 typedef union
25 {
26 double value;
27 struct
28 {
29 u_int32_t msw;
30 u_int32_t lsw;
31 } parts;
32 } ieee_double_shape_type;
33
34 #endif
35
36 #if (BYTE_ORDER == LITTLE_ENDIAN) && !(defined(__arm__) && !defined(__VFP_FP__))
37
38 typedef union
39 {
40 double value;
41 struct
42 {
43 u_int32_t lsw;
44 u_int32_t msw;
45 } parts;
46 } ieee_double_shape_type;
47
48 #endif
49
50 /* Get two 32 bit ints from a double. */
51
52 #define EXTRACT_WORDS(ix0,ix1,d) \
53 do { \
54 ieee_double_shape_type ew_u; \
55 ew_u.value = (d); \
56 (ix0) = ew_u.parts.msw; \
57 (ix1) = ew_u.parts.lsw; \
58 } while (0)
59
60 /* Get the more significant 32 bit int from a double. */
61
62 #define GET_HIGH_WORD(i,d) \
63 do { \
64 ieee_double_shape_type gh_u; \
65 gh_u.value = (d); \
66 (i) = gh_u.parts.msw; \
67 } while (0)
68
69 /* Set the more significant 32 bits of a double from an int. */
70
71 #define SET_HIGH_WORD(d,v) \
72 do { \
73 ieee_double_shape_type sh_u; \
74 sh_u.value = (d); \
75 sh_u.parts.msw = (v); \
76 (d) = sh_u.value; \
77 } while (0)
78
79
80 static const double
81 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
82 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
83 huge = 1.0e+300,
84 tiny = 1.0e-300;
85
86 static double
_copysign(double x,double y)87 _copysign(double x, double y)
88 {
89 u_int32_t hx,hy;
90 GET_HIGH_WORD(hx,x);
91 GET_HIGH_WORD(hy,y);
92 SET_HIGH_WORD(x,(hx&0x7fffffff)|(hy&0x80000000));
93 return x;
94 }
95
96 double
ldexp(double x,int n)97 ldexp(double x, int n)
98 {
99 int32_t k,hx,lx;
100 EXTRACT_WORDS(hx,lx,x);
101 k = (hx&0x7ff00000)>>20; /* extract exponent */
102 if (k==0) { /* 0 or subnormal x */
103 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
104 x *= two54;
105 GET_HIGH_WORD(hx,x);
106 k = ((hx&0x7ff00000)>>20) - 54;
107 if (n< -50000) return tiny*x; /*underflow*/
108 }
109 if (k==0x7ff) return x+x; /* NaN or Inf */
110 k = k+n;
111 if (k > 0x7fe) return huge*_copysign(huge,x); /* overflow */
112 if (k > 0) /* normal result */
113 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
114 if (k <= -54) {
115 if (n > 50000) /* in case integer overflow in n+k */
116 return huge*_copysign(huge,x); /*overflow*/
117 else return tiny*_copysign(tiny,x); /*underflow*/
118 }
119 k += 54; /* subnormal result */
120 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
121 return x*twom54;
122 }
123 DEF_STRONG(ldexp);
124
125 #if LDBL_MANT_DIG == DBL_MANT_DIG
126 __strong_alias(ldexpl, ldexp);
127 #endif /* LDBL_MANT_DIG == DBL_MANT_DIG */
128