1 /*
2  * The authors of this software are Rob Pike and Ken Thompson.
3  *              Copyright (c) 2002 by Lucent Technologies.
4  * Permission to use, copy, modify, and distribute this software for any
5  * purpose without fee is hereby granted, provided that this entire notice
6  * is included in all copies of any software which is or includes a copy
7  * or modification of this software and in all copies of the supporting
8  * documentation for such software.
9  * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
10  * WARRANTY.  IN PARTICULAR, NEITHER THE AUTHORS NOR LUCENT TECHNOLOGIES MAKE ANY
11  * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
12  * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
13  */
14 #include <stdarg.h>
15 #include <string.h>
16 #include "utf.h"
17 #include "fmt.h"
18 #include "fmtdef.h"
19 
20 /*
21  * this table might overflow 127-bit exponent representations.
22  * in that case, truncate it after 1.0e38.
23  * it is important to get all one can from this
24  * routine since it is used in atof to scale numbers.
25  * the presumption is that C converts fp numbers better
26  * than multipication of lower powers of 10.
27  */
28 
29 static
30 double	tab[] =
31 {
32 	1.0e0, 1.0e1, 1.0e2, 1.0e3, 1.0e4, 1.0e5, 1.0e6, 1.0e7, 1.0e8, 1.0e9,
33 	1.0e10,1.0e11,1.0e12,1.0e13,1.0e14,1.0e15,1.0e16,1.0e17,1.0e18,1.0e19,
34 	1.0e20,1.0e21,1.0e22,1.0e23,1.0e24,1.0e25,1.0e26,1.0e27,1.0e28,1.0e29,
35 	1.0e30,1.0e31,1.0e32,1.0e33,1.0e34,1.0e35,1.0e36,1.0e37,1.0e38,1.0e39,
36 	1.0e40,1.0e41,1.0e42,1.0e43,1.0e44,1.0e45,1.0e46,1.0e47,1.0e48,1.0e49,
37 	1.0e50,1.0e51,1.0e52,1.0e53,1.0e54,1.0e55,1.0e56,1.0e57,1.0e58,1.0e59,
38 	1.0e60,1.0e61,1.0e62,1.0e63,1.0e64,1.0e65,1.0e66,1.0e67,1.0e68,1.0e69,
39 };
40 
41 double
42 __fmtpow10(int n)
43 {
44 	int m;
45 
46 	if(n < 0) {
47 		n = -n;
48 		if(n < (int)(sizeof(tab)/sizeof(tab[0])))
49 			return 1/tab[n];
50 		m = n/2;
51 		return __fmtpow10(-m) * __fmtpow10(m-n);
52 	}
53 	if(n < (int)(sizeof(tab)/sizeof(tab[0])))
54 		return tab[n];
55 	m = n/2;
56 	return __fmtpow10(m) * __fmtpow10(n-m);
57 }