java - Using recursive power function in log function, without Math.functions -

like says in title have problem i'm required make own power , log methodss , use them on input. power function seems fine until try use in loga(b) function. 1 problem don't understand loop in log method copied 1 in class understand later. problem don't know how built in math.pow() works, if had code or pseudocode guess how own power function different. in advance , please go easy on me i'm still quite new of this.

import java.util.scanner;  public class numbers {      public static void main(string[] args) {         scanner input = new scanner(system.in);         double i1;         double i2;         system.out.print("type a:");         i1 = input.nextdouble();         system.out.print("type b:");         i2 = input.nextdouble();         input.close();         sumrange(i1, i2);         power(i1, i2);         log(i1, i2);         system.out.println("sum b: " + sumrange(i1, i2) + "\nfibonacci a: " + fibonacci(i1)                 + "\nfibonacci b: " + fibonacci(i2) + "\na^b:" + power(i1, i2) + "\na%b: " + mod(i1, i2)                 + "\nloga (b)" + log(i1, i2));     }      // if i'm honest don't understand how log code works exactly,     // know code calculates correct log     // math.pow() function     // own power function doesn't seem work , don't know how     // math.pow()     // function different mine     static double log(double i1, double i2) {         double value = 0;         (double = 1; > .001; /= 10) {             while (!(power(i1, value) > i2)) {                 value += i;             }             value -= i;         }         return value;     }      static double power(double i1, double i2) {         if (i2 == 0) {             return 1;         }         if (i2 == 1) {             return i1;         }         // line below seems cause problems since used in log(double,         // double) method         return i1 * power(i1, i2 - 1);     }     // excluded 3 other methods work fine , don't depend on      // each other work 

your power method works integer i2, else recursion never terminate.

for non-integer i2 @ least linear interpolation after reduction between 0 , 1. bad approximation large basis values i1 better nothing.

    if( 0<=i2 , i2 <=1) return 1+i2*(i1-1); 

what negative i2?

    if( i2 < 0 ) return 1/power(i1,-i2); 

google "libm/exp.c" professional implementations of exponential in c standard library, there different variants, , "libm/pow.c".