question: protected static Dfp expInternal ( final Dfp a ) { Dfp y = a . getOne ( ) ; Dfp x = a . getOne ( ) ; Dfp fact = a . getOne ( ) ; Dfp py = new Dfp ( y ) ; for ( int i = 1 ; i < 90 ; i ++ ) { x = x . multiply ( a ) ; fact = fact . divide ( i ) ; y = y . add ( x . multiply ( fact ) ) ; if ( y . equals ( py ) ) { break ; } py = new Dfp ( y ) ; } return y ; }
target:  Computes e to the given power. Where -1 < a < 1.  Use the classic Taylor series.  1 + x**2/2! + x**3/3! + x**4/4!  ...