pow10.c (1989B)
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 11 * ANY 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 "plan9.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 }