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
24typedef 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
38typedef 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)				\
53do {								\
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)					\
63do {								\
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)					\
72do {								\
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
80static const double
81two54   =  1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
82twom54  =  5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
83huge   = 1.0e+300,
84tiny   = 1.0e-300;
85
86static double
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
96double
97ldexp(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}
123DEF_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