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 #ifndef lint
14 static char rcsid[] = "$FreeBSD$";
15 #endif
16
17 /*
18 * scalbn (double x, int n)
19 * scalbn(x,n) returns x* 2**n computed by exponent
20 * manipulation rather than by actually performing an
21 * exponentiation or a multiplication.
22 */
23
24 #include <sys/cdefs.h>
25 #include <float.h>
26
27 #include "math.h"
28 #include "math_private.h"
29
30 static const double
31 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
32 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
33 huge = 1.0e+300,
34 tiny = 1.0e-300;
35
36 double
scalbn(double x,int n)37 scalbn (double x, int n)
38 {
39 int32_t k,hx,lx;
40 EXTRACT_WORDS(hx,lx,x);
41 k = (hx&0x7ff00000)>>20; /* extract exponent */
42 if (k==0) { /* 0 or subnormal x */
43 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
44 x *= two54;
45 GET_HIGH_WORD(hx,x);
46 k = ((hx&0x7ff00000)>>20) - 54;
47 if (n< -50000) return tiny*x; /*underflow*/
48 }
49 if (k==0x7ff) return x+x; /* NaN or Inf */
50 k = k+n;
51 if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */
52 if (k > 0) /* normal result */
53 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
54 if (k <= -54)
55 if (n > 50000) /* in case integer overflow in n+k */
56 return huge*copysign(huge,x); /*overflow*/
57 else return tiny*copysign(tiny,x); /*underflow*/
58 k += 54; /* subnormal result */
59 SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));
60 return x*twom54;
61 }
62
63 #if (LDBL_MANT_DIG == 53)
64 __weak_reference(scalbn, ldexpl);
65 __weak_reference(scalbn, scalbnl);
66 #endif
67