92 lines
1.8 KiB
Go
92 lines
1.8 KiB
Go
package main
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import (
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"flag"
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"fmt"
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"sync"
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)
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func main() {
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start, max, step, printCount := parseArgs()
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if max < start {
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start, max = max, start
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}
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totalLength := max - start
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if totalLength < step {
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step = totalLength
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}
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// Start jobs
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var wg sync.WaitGroup
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results := make(chan int, 100)
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for i := start; i < max; i += step {
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wg.Add(1)
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go worker(i, i+step, &wg, results)
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}
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// Collect results
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go waitForWorkers(&wg, results)
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var primes []int
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for prime := range results {
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primes = append(primes, prime)
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}
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// Print results
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fmt.Println("There are", len(primes), "primes between", start, "and", max)
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if printCount > len(primes) {
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printCount = -1
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}
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if printCount < 0 {
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fmt.Println("Here they are:")
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fmt.Println(primes)
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} else {
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fmt.Println("Here's a free sample:")
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fmt.Println(primes[:printCount])
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}
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}
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func worker(start, end int, wg *sync.WaitGroup, results chan<- int) {
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defer wg.Done()
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for i := start; i < end; i++ {
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if IsPrime(i) {
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results <- i
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}
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}
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}
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func waitForWorkers(wg *sync.WaitGroup, results chan int) {
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wg.Wait()
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close(results)
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}
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// IsPrime determines if the given int is a prime number or not.
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// The method currently implemented by this method is not smart and not
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// optimized for large numbers.
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func IsPrime(n int) bool {
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if n <= 3 {
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return n > 1
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}
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if n%2 == 0 || n%3 == 0 {
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return false
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}
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i := 5
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for i*i <= n {
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if n%i == 0 || n%(i+2) == 0 {
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return false
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}
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i += 6
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}
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return true
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}
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func parseArgs() (start, max, step, printCount int) {
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flag.IntVar(&start, "start", 0, "The start number")
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flag.IntVar(&max, "max", 10_000, "The end value")
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flag.IntVar(&step, "step-size", 1_000, "The job size")
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printCountDesc := `Number of primes to print. -1 to print all.
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Primes are not guaranteed to be sorted.`
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flag.IntVar(&printCount, "print-count", 20, printCountDesc)
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flag.Parse()
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return
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}
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