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