1/* s_scalbnl.c -- long double version of s_scalbn.c.
2 */
3
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/*
16 * scalbnl (long double x, int n)
17 * scalbnl(x,n) returns x* 2**n computed by exponent
18 * manipulation rather than by actually performing an
19 * exponentiation or a multiplication.
20 */
21
22#include <math.h>
23#include <math_private.h>
24
25static const long double
26two63 = 0x1p63L,
27twom64 = 0x1p-64L,
28huge = 1.0e+4900L,
29tiny = 1.0e-4900L;
30
31long double
32__scalblnl (long double x, long int n)
33{
34 int32_t k,es,hx,lx;
35 GET_LDOUBLE_WORDS(es,hx,lx,x);
36 k = es&0x7fff; /* extract exponent */
37 if (__builtin_expect(k==0, 0)) { /* 0 or subnormal x */
38 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
39 x *= two63;
40 GET_LDOUBLE_EXP(es,x);
41 k = (es&0x7fff) - 63;
42 }
43 if (__builtin_expect(k==0x7fff, 0)) return x+x; /* NaN or Inf */
44 if (__builtin_expect(n< -50000, 0))
45 return tiny*copysignl(tiny,x);
46 if (__builtin_expect(n> 50000 || k+n > 0x7ffe, 0))
47 return huge*copysignl(huge,x); /* overflow */
48 /* Now k and n are bounded we know that k = k+n does not
49 overflow. */
50 k = k+n;
51 if (__builtin_expect(k > 0, 1)) /* normal result */
52 {SET_LDOUBLE_EXP(x,(es&0x8000)|k); return x;}
53 if (k <= -64)
54 return tiny*copysignl(tiny,x); /*underflow*/
55 k += 64; /* subnormal result */
56 SET_LDOUBLE_EXP(x,(es&0x8000)|k);
57 return x*twom64;
58}
59

source code of glibc/sysdeps/ieee754/ldbl-96/s_scalblnl.c