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
25typedef 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
39typedef 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)				\
54do {								\
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)					\
64do {								\
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)					\
73do {								\
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
81static const double
82two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
83twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
84huge   = 1.0e+300,
85tiny   = 1.0e-300;
86
87static double
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
97double
98ldexp(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