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 | |
25 | static const long double |
26 | two63 = 0x1p63L, |
27 | twom64 = 0x1p-64L, |
28 | huge = 1.0e+4900L, |
29 | tiny = 1.0e-4900L; |
30 | |
31 | long 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 | |