pow10.c (1301B)
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 }