primes/primes.go

package main

// Go version of a prime number finder

import(
	"fmt"
	"os"
	"strconv"
	"math"
)

// In stead of in place printing of each prime, it seems 
// fmt.Println is costly, and causes the program to take
// 7x more time, so we gain speed at the expense of RAM
// by storing them all in a slice and printing once
func main() {
	if len(os.Args) < 2 {
		fmt.Println("Usage: go run primes.go [MAX]")
		return
	}
	primes := make([]int, 0)
	max,_ := strconv.Atoi(os.Args[1])
	for i:= 3; i < max; i+=2 {
		is_prime := true
		for j := 3; j <= int(math.Ceil(math.Sqrt(float64(i)))); j+=2 {
			if i % j == 0 {
				is_prime = false
				break
			}
		}
		if is_prime {
			primes = append(primes, i)
		}
	}
	fmt.Println(primes)
}