Golang tour #55

go_tour_55.go

package main

import (
    "fmt"
    "math"
)

type ErrNegativeSqrt float64

func (e ErrNegativeSqrt) Error() string {
    return fmt.Sprintf("cannot Sqrt negative number: %d", int64(e))   
}

func Sqrt(f float64) (float64, error) {
    if f < 0 {
     	return f, ErrNegativeSqrt(f) 
    } 
    guess := f/2
    t := 0.0
    threshold := 0.0000001
    for math.Abs(guess - t) > threshold {
        	t = guess
    		guess = guess - (guess*guess-f)/(2*guess) 
    }
	return guess, nil

}

func main() {
    fmt.Println(Sqrt(2))
    fmt.Println(Sqrt(-2))
}