eratosthenes_parallel/eratosthenes_parallel.go

package main

import (
	"fmt"
	"os"
	"strconv"
	"time"
)

func main() {
	n, err := strconv.ParseInt(os.Args[1], 10, 64)
	if err != nil {
		panic(err)
	}
	t0 := time.Now()
	sieve := make([]uint64, (n>>7)+1)
	var found int64
	var i int64
	i = 2
	found++
	for i = 3; i < n; i += 2 {
		if (sieve[i>>7] & (1 << ((i & 0x7F) >> 1))) == 0 {
			found++
			for j := i * i; j < n; j += 2 * i {
				sieve[j>>7] |= 1 << ((j & 0x7F) >> 1)
			}
		}
	}
	d := time.Since(t0)
	fmt.Println()
	fmt.Println(found, "primes found in", d)

}