1 /* @(#)s_scalbn.c 5.1 93/09/24 */
2 /*
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5 *
6 * Developed at SunPro, a Sun Microsystems, Inc. business.
7 * Permission to use, copy, modify, and distribute this
8 * software is freely granted, provided that this notice
9 * is preserved.
10 * ====================================================
11 */
12
13 /*
14 * scalbn (double x, int n)
15 * scalbn(x,n) returns x* 2**n computed by exponent
16 * manipulation rather than by actually performing an
17 * exponentiation or a multiplication.
18 */
19
20 #include "fdlibm.h"
21
22 #ifdef _NEED_FLOAT64
23
24 static const __float64
25 two54 = _F_64(1.80143985094819840000e+16), /* 0x43500000, 0x00000000 */
26 twom54 = _F_64(5.55111512312578270212e-17); /* 0x3C900000, 0x00000000 */
27
28 __float64
scalbln64(__float64 x,long int n)29 scalbln64 (__float64 x, long int n)
30 {
31 __int32_t hx,lx;
32 long int k;
33 EXTRACT_WORDS(hx,lx,x);
34 k = (hx&0x7ff00000)>>20; /* extract exponent */
35 if (k==0) { /* 0 or subnormal x */
36 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
37 x *= two54;
38 GET_HIGH_WORD(hx,x);
39 k = ((hx&0x7ff00000)>>20) - 54;
40 if (n< -50000) return __math_uflow(hx < 0); /*underflow*/
41 }
42 if (k==0x7ff) return x+x; /* NaN or Inf */
43 k = k+n;
44 if (n> 50000 || k > 0x7fe)
45 return __math_oflow(hx<0); /* overflow */
46 if (k > 0) /* normal result */
47 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
48 if (k <= -54)
49 return __math_uflow(hx < 0); /*underflow*/
50 k += 54; /* subnormal result */
51 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
52 return check_uflow(x*twom54);
53 }
54
55 _MATH_ALIAS_d_dj(scalbln)
56
57 #endif /* _NEED_FLOAT64 */
58
