1*2f2c0062Sguenther /* $OpenBSD: s_scalbnl.c,v 1.4 2016/09/12 19:47:02 guenther Exp $ */
2390c8400Smartynas /* @(#)s_scalbn.c 5.1 93/09/24 */
3390c8400Smartynas /*
4390c8400Smartynas * ====================================================
5390c8400Smartynas * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6390c8400Smartynas *
7390c8400Smartynas * Developed at SunPro, a Sun Microsystems, Inc. business.
8390c8400Smartynas * Permission to use, copy, modify, and distribute this
9390c8400Smartynas * software is freely granted, provided that this notice
10390c8400Smartynas * is preserved.
11390c8400Smartynas * ====================================================
12390c8400Smartynas */
13390c8400Smartynas
14390c8400Smartynas /*
15390c8400Smartynas * scalbnl (long double x, int n)
16390c8400Smartynas * scalbnl(x,n) returns x* 2**n computed by exponent
17390c8400Smartynas * manipulation rather than by actually performing an
18390c8400Smartynas * exponentiation or a multiplication.
19390c8400Smartynas */
20390c8400Smartynas
21390c8400Smartynas /*
22390c8400Smartynas * We assume that a long double has a 15-bit exponent. On systems
23390c8400Smartynas * where long double is the same as double, scalbnl() is an alias
24390c8400Smartynas * for scalbn(), so we don't use this routine.
25390c8400Smartynas */
26390c8400Smartynas
27390c8400Smartynas #include <sys/types.h>
28390c8400Smartynas #include <machine/ieee.h>
29390c8400Smartynas #include <float.h>
30390c8400Smartynas #include <math.h>
31390c8400Smartynas
32390c8400Smartynas #if LDBL_MAX_EXP != 0x4000
33390c8400Smartynas #error "Unsupported long double format"
34390c8400Smartynas #endif
35390c8400Smartynas
36390c8400Smartynas static const long double
37390c8400Smartynas huge = 0x1p16000L,
38390c8400Smartynas tiny = 0x1p-16000L;
39390c8400Smartynas
40390c8400Smartynas long double
scalbnl(long double x,int n)41390c8400Smartynas scalbnl (long double x, int n)
42390c8400Smartynas {
43390c8400Smartynas union {
44390c8400Smartynas long double e;
45390c8400Smartynas struct ieee_ext bits;
46390c8400Smartynas } u;
47390c8400Smartynas int k;
48390c8400Smartynas u.e = x;
49390c8400Smartynas k = u.bits.ext_exp; /* extract exponent */
50390c8400Smartynas if (k==0) { /* 0 or subnormal x */
51390c8400Smartynas if ((u.bits.ext_frach
52390c8400Smartynas #ifdef EXT_FRACHMBITS
53390c8400Smartynas | u.bits.ext_frachm
54390c8400Smartynas #endif /* EXT_FRACHMBITS */
55390c8400Smartynas #ifdef EXT_FRACLMBITS
56390c8400Smartynas | u.bits.ext_fraclm
57390c8400Smartynas #endif /* EXT_FRACLMBITS */
58390c8400Smartynas | u.bits.ext_fracl)==0) return x; /* +-0 */
59390c8400Smartynas u.e *= 0x1p+128;
60390c8400Smartynas k = u.bits.ext_exp - 128;
61390c8400Smartynas if (n< -50000) return tiny*x; /*underflow*/
62390c8400Smartynas }
63390c8400Smartynas if (k==0x7fff) return x+x; /* NaN or Inf */
64390c8400Smartynas k = k+n;
65390c8400Smartynas if (k >= 0x7fff) return huge*copysignl(huge,x); /* overflow */
66390c8400Smartynas if (k > 0) /* normal result */
67390c8400Smartynas {u.bits.ext_exp = k; return u.e;}
6896943daaSmartynas if (k <= -128) {
69390c8400Smartynas if (n > 50000) /* in case integer overflow in n+k */
70390c8400Smartynas return huge*copysign(huge,x); /*overflow*/
71390c8400Smartynas else return tiny*copysign(tiny,x); /*underflow*/
7296943daaSmartynas }
73390c8400Smartynas k += 128; /* subnormal result */
74390c8400Smartynas u.bits.ext_exp = k;
75390c8400Smartynas return u.e*0x1p-128;
76390c8400Smartynas }
77*2f2c0062Sguenther DEF_STD(scalbnl);
78390c8400Smartynas
79390c8400Smartynas long double
ldexpl(long double x,int n)80390c8400Smartynas ldexpl(long double x, int n)
81390c8400Smartynas {
82390c8400Smartynas return scalbnl(x, n);
83390c8400Smartynas }
84*2f2c0062Sguenther DEF_STD(ldexpl);
85