1 /*
2 * The authors of this software are Rob Pike and Ken Thompson,
3 * with contributions from Mike Burrows and Sean Dorward.
4 *
5 * Copyright (c) 2002-2006 by Lucent Technologies.
6 * Portions Copyright (c) 2004 Google Inc.
7 *
8 * Permission to use, copy, modify, and distribute this software for any
9 * purpose without fee is hereby granted, provided that this entire notice
10 * is included in all copies of any software which is or includes a copy
11 * or modification of this software and in all copies of the supporting
12 * documentation for such software.
13 * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
14 * WARRANTY. IN PARTICULAR, NEITHER THE AUTHORS NOR LUCENT TECHNOLOGIES
15 * NOR GOOGLE INC MAKE ANY REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING
16 * THE MERCHANTABILITY OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
17 */
18
19 #include <u.h>
20 #include <libc.h>
21 #include "fmtdef.h"
22
23 /*
24 * this table might overflow 127-bit exponent representations.
25 * in that case, truncate it after 1.0e38.
26 * it is important to get all one can from this
27 * routine since it is used in atof to scale numbers.
28 * the presumption is that C converts fp numbers better
29 * than multipication of lower powers of 10.
30 */
31
32 static
33 double tab[] =
34 {
35 1.0e0, 1.0e1, 1.0e2, 1.0e3, 1.0e4, 1.0e5, 1.0e6, 1.0e7, 1.0e8, 1.0e9,
36 1.0e10,1.0e11,1.0e12,1.0e13,1.0e14,1.0e15,1.0e16,1.0e17,1.0e18,1.0e19,
37 1.0e20,1.0e21,1.0e22,1.0e23,1.0e24,1.0e25,1.0e26,1.0e27,1.0e28,1.0e29,
38 1.0e30,1.0e31,1.0e32,1.0e33,1.0e34,1.0e35,1.0e36,1.0e37,1.0e38,1.0e39,
39 1.0e40,1.0e41,1.0e42,1.0e43,1.0e44,1.0e45,1.0e46,1.0e47,1.0e48,1.0e49,
40 1.0e50,1.0e51,1.0e52,1.0e53,1.0e54,1.0e55,1.0e56,1.0e57,1.0e58,1.0e59,
41 1.0e60,1.0e61,1.0e62,1.0e63,1.0e64,1.0e65,1.0e66,1.0e67,1.0e68,1.0e69,
42 };
43
44 double
45 __fmtpow10(int n)
46 {
47 int m;
48
49 if(n < 0) {
50 n = -n;
51 if(n < (int)(sizeof(tab)/sizeof(tab[0])))
52 return 1/tab[n];
53 m = n/2;
54 return __fmtpow10(-m) * __fmtpow10(m-n);
55 }
56 if(n < (int)(sizeof(tab)/sizeof(tab[0])))
57 return tab[n];
58 m = n/2;
59 return __fmtpow10(m) * __fmtpow10(n-m);
60 }