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 <sys/cdefs.h>
21 #include <float.h>
22
23 #include "math.h"
24 #include "math_private.h"
25
26 static const double
27 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
28 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
29 huge = 1.0e+300,
30 tiny = 1.0e-300;
31
32 double
scalbn(double x,int n)33 scalbn (double x, int n)
34 {
35 int32_t k,hx,lx;
36 EXTRACT_WORDS(hx,lx,x);
37 k = (hx&0x7ff00000)>>20; /* extract exponent */
38 if (k==0) { /* 0 or subnormal x */
39 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
40 x *= two54;
41 GET_HIGH_WORD(hx,x);
42 k = ((hx&0x7ff00000)>>20) - 54;
43 if (n< -50000) return tiny*x; /*underflow*/
44 }
45 if (k==0x7ff) return x+x; /* NaN or Inf */
46 k = k+n;
47 if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */
48 if (k > 0) /* normal result */
49 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
50
51 if (k <= -54) {
52 if (n > 50000) { /* in case integer overflow in n+k */
53 return huge*copysign(huge,x); /*overflow*/
54 } else {
55 return tiny*copysign(tiny,x); /*underflow*/
56 }
57 }
58 k += 54; /* subnormal result */
59 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
60 return x*twom54;
61 }
62
63 #if SUPPORT_LONG_DOUBLE
64
65 #if (LDBL_MANT_DIG == 53)
66 __weak_reference(scalbn, ldexpl);
67 __weak_reference(scalbn, scalbnl);
68 #endif
69
70 #endif
71