1 #include <u.h> 2 #include <libc.h> 3 4 /* 5 * this table might overflow 127-bit exponent representations. 6 * in that case, truncate it after 1.0e38. 7 * it is important to get all one can from this 8 * routine since it is used in atof to scale numbers. 9 * the presumption is that C converts fp numbers better 10 * than multipication of lower powers of 10. 11 */ 12 13 static 14 double tab[] = 15 { 16 1.0e0, 1.0e1, 1.0e2, 1.0e3, 1.0e4, 1.0e5, 1.0e6, 1.0e7, 1.0e8, 1.0e9, 17 1.0e10,1.0e11,1.0e12,1.0e13,1.0e14,1.0e15,1.0e16,1.0e17,1.0e18,1.0e19, 18 1.0e20,1.0e21,1.0e22,1.0e23,1.0e24,1.0e25,1.0e26,1.0e27,1.0e28,1.0e29, 19 1.0e30,1.0e31,1.0e32,1.0e33,1.0e34,1.0e35,1.0e36,1.0e37,1.0e38,1.0e39, 20 1.0e40,1.0e41,1.0e42,1.0e43,1.0e44,1.0e45,1.0e46,1.0e47,1.0e48,1.0e49, 21 1.0e50,1.0e51,1.0e52,1.0e53,1.0e54,1.0e55,1.0e56,1.0e57,1.0e58,1.0e59, 22 1.0e60,1.0e61,1.0e62,1.0e63,1.0e64,1.0e65,1.0e66,1.0e67,1.0e68,1.0e69, 23 }; 24 25 double 26 pow10(int n) 27 { 28 int m; 29 30 if(n < 0) { 31 n = -n; 32 if(n < sizeof(tab)/sizeof(tab[0])) 33 return 1/tab[n]; 34 m = n/2; 35 return pow10(-m) * pow10(m-n); 36 } 37 if(n < sizeof(tab)/sizeof(tab[0])) 38 return tab[n]; 39 m = n/2; 40 return pow10(m) * pow10(n-m); 41 } 42