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2aa62f2b | 1 | /* @(#)s_scalbn.c 5.1 93/09/24 */\r |
2 | /*\r | |
3 | * ====================================================\r | |
4 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.\r | |
5 | *\r | |
6 | * Developed at SunPro, a Sun Microsystems, Inc. business.\r | |
7 | * Permission to use, copy, modify, and distribute this\r | |
8 | * software is freely granted, provided that this notice\r | |
9 | * is preserved.\r | |
10 | * ====================================================\r | |
11 | */\r | |
12 | #include <LibConfig.h>\r | |
13 | #include <sys/EfiCdefs.h>\r | |
14 | #if defined(LIBM_SCCS) && !defined(lint)\r | |
15 | __RCSID("$NetBSD: s_scalbn.c,v 1.12 2002/05/26 22:01:58 wiz Exp $");\r | |
16 | #endif\r | |
17 | \r | |
18 | /*\r | |
19 | * scalbn (double x, int n)\r | |
20 | * scalbn(x,n) returns x* 2**n computed by exponent\r | |
21 | * manipulation rather than by actually performing an\r | |
22 | * exponentiation or a multiplication.\r | |
23 | */\r | |
24 | \r | |
25 | #include "math.h"\r | |
26 | #include "math_private.h"\r | |
27 | \r | |
28 | static const double\r | |
29 | two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */\r | |
30 | twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */\r | |
31 | huge = 1.0e+300,\r | |
32 | tiny = 1.0e-300;\r | |
33 | \r | |
34 | double\r | |
35 | scalbn(double x, int n)\r | |
36 | {\r | |
37 | int32_t k,hx,lx;\r | |
38 | EXTRACT_WORDS(hx,lx,x);\r | |
39 | k = (hx&0x7ff00000)>>20; /* extract exponent */\r | |
40 | if (k==0) { /* 0 or subnormal x */\r | |
41 | if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */\r | |
42 | x *= two54;\r | |
43 | GET_HIGH_WORD(hx,x);\r | |
44 | k = ((hx&0x7ff00000)>>20) - 54;\r | |
45 | if (n< -50000) return tiny*x; /*underflow*/\r | |
46 | }\r | |
47 | if (k==0x7ff) return x+x; /* NaN or Inf */\r | |
48 | k = k+n;\r | |
49 | if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */\r | |
50 | if (k > 0) /* normal result */\r | |
51 | {SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20)); return x;}\r | |
52 | if (k <= -54) {\r | |
53 | if (n > 50000) /* in case integer overflow in n+k */\r | |
54 | return huge*copysign(huge,x); /*overflow*/\r | |
55 | else return tiny*copysign(tiny,x); /*underflow*/\r | |
56 | }\r | |
57 | k += 54; /* subnormal result */\r | |
58 | SET_HIGH_WORD(x,(hx&0x800fffff)|(k<<20));\r | |
59 | return x*twom54;\r | |
60 | }\r |