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 #include <sys/cdefs.h>
14 __FBSDID("$FreeBSD: head/lib/msun/src/s_scalbn.c 306409 2016-09-28 14:48:34Z emaste $");
15
16 /*
17 * scalbn (double x, int n)
18 * scalbn(x,n) returns x* 2**n computed by exponent
19 * manipulation rather than by actually performing an
20 * exponentiation or a multiplication.
21 */
22
23 #include <float.h>
24
25 #include "math.h"
26 #include "math_private.h"
27
28 static const double
29 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
30 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
31 huge = 1.0e+300,
32 tiny = 1.0e-300;
33
34 double
scalbn(double x,int n)35 scalbn (double x, int n)
36 {
37 int32_t k,hx,lx;
38 EXTRACT_WORDS(hx,lx,x);
39 k = (hx&0x7ff00000)>>20; /* extract exponent */
40 if (k==0) { /* 0 or subnormal x */
41 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
42 x *= two54;
43 GET_HIGH_WORD(hx,x);
44 k = ((hx&0x7ff00000)>>20) - 54;
45 if (n< -50000) return tiny*x; /*underflow*/
46 }
47 if (k==0x7ff) return x+x; /* NaN or Inf */
48 k = k+n;
49 if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */
50 if (k > 0) /* normal result */
51 {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}
52 if (k <= -54) {
53 if (n > 50000) /* in case integer overflow in n+k */
54 return huge*copysign(huge,x); /*overflow*/
55 else
56 return tiny*copysign(tiny,x); /*underflow*/
57 }
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