1 /* Copyright (c) 2002-2006 Lucent Technologies; see LICENSE */
2 #include <stdarg.h>
3 #include <string.h>
4 #include "plan9.h"
5 #include "fmt.h"
6 #include "fmtdef.h"
7 
8 /*
9  * this table might overflow 127-bit exponent representations.
10  * in that case, truncate it after 1.0e38.
11  * it is important to get all one can from this
12  * routine since it is used in atof to scale numbers.
13  * the presumption is that C converts fp numbers better
14  * than multipication of lower powers of 10.
15  */
16 
17 static
18 double	tab[] =
19 {
20 	1.0e0, 1.0e1, 1.0e2, 1.0e3, 1.0e4, 1.0e5, 1.0e6, 1.0e7, 1.0e8, 1.0e9,
21 	1.0e10,1.0e11,1.0e12,1.0e13,1.0e14,1.0e15,1.0e16,1.0e17,1.0e18,1.0e19,
22 	1.0e20,1.0e21,1.0e22,1.0e23,1.0e24,1.0e25,1.0e26,1.0e27,1.0e28,1.0e29,
23 	1.0e30,1.0e31,1.0e32,1.0e33,1.0e34,1.0e35,1.0e36,1.0e37,1.0e38,1.0e39,
24 	1.0e40,1.0e41,1.0e42,1.0e43,1.0e44,1.0e45,1.0e46,1.0e47,1.0e48,1.0e49,
25 	1.0e50,1.0e51,1.0e52,1.0e53,1.0e54,1.0e55,1.0e56,1.0e57,1.0e58,1.0e59,
26 	1.0e60,1.0e61,1.0e62,1.0e63,1.0e64,1.0e65,1.0e66,1.0e67,1.0e68,1.0e69,
27 };
28 
29 double
30 __fmtpow10(int n)
31 {
32 	int m;
33 
34 	if(n < 0) {
35 		n = -n;
36 		if(n < (int)(sizeof(tab)/sizeof(tab[0])))
37 			return 1/tab[n];
38 		m = n/2;
39 		return __fmtpow10(-m) * __fmtpow10(m-n);
40 	}
41 	if(n < (int)(sizeof(tab)/sizeof(tab[0])))
42 		return tab[n];
43 	m = n/2;
44 	return __fmtpow10(m) * __fmtpow10(n-m);
45 }