ref: e71d63cae5e8311ba172328b992b3e4ca8f47fb5
dir: /libc/pow10.c/
#include <u.h>
#include <libc.h>
#include "fmtdef.h"
/*
* this table might overflow 127-bit exponent representations.
* in that case, truncate it after 1.0e38.
* it is important to get all one can from this
* routine since it is used in atof to scale numbers.
* the presumption is that C converts fp numbers better
* than multipication of lower powers of 10.
*/
static
double tab[] =
{
1.0e0, 1.0e1, 1.0e2, 1.0e3, 1.0e4, 1.0e5, 1.0e6, 1.0e7, 1.0e8, 1.0e9,
1.0e10,1.0e11,1.0e12,1.0e13,1.0e14,1.0e15,1.0e16,1.0e17,1.0e18,1.0e19,
1.0e20,1.0e21,1.0e22,1.0e23,1.0e24,1.0e25,1.0e26,1.0e27,1.0e28,1.0e29,
1.0e30,1.0e31,1.0e32,1.0e33,1.0e34,1.0e35,1.0e36,1.0e37,1.0e38,1.0e39,
1.0e40,1.0e41,1.0e42,1.0e43,1.0e44,1.0e45,1.0e46,1.0e47,1.0e48,1.0e49,
1.0e50,1.0e51,1.0e52,1.0e53,1.0e54,1.0e55,1.0e56,1.0e57,1.0e58,1.0e59,
1.0e60,1.0e61,1.0e62,1.0e63,1.0e64,1.0e65,1.0e66,1.0e67,1.0e68,1.0e69,
};
double
__fmtpow10(int n)
{
int m;
if(n < 0) {
n = -n;
if(n < (int)(sizeof(tab)/sizeof(tab[0])))
return 1/tab[n];
m = n/2;
return __fmtpow10(-m) * __fmtpow10(m-n);
}
if(n < (int)(sizeof(tab)/sizeof(tab[0])))
return tab[n];
m = n/2;
return __fmtpow10(m) * __fmtpow10(n-m);
}