Add primes program

.gitignore

@@ -0,0 +1,3 @@
+primes
+primes.txt
+*.tar.gz

primes.go

@@ -0,0 +1,68 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"bufio"
+	"strconv"
+	"runtime"
+)
+
+var ch chan uint64
+
+func check(e error) {
+    if e != nil {
+        panic(e)
+    }
+}
+
+func main() {
+	ch = make(chan uint64)
+	numThreads := runtime.NumCPU()
+	fmt.Printf("Starting to calculate primes\n")
+	f, err := os.OpenFile("primes.txt", os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
+	check(err)
+	defer f.Close()
+	w := bufio.NewWriter(f)
+	defer w.Flush()
+	start := uint64(1)
+	if len(os.Args) >= 2 {
+		start, err = strconv.ParseUint(os.Args[1], 10, 64)
+		check(err)
+	}
+	if start % 2 == 0 {
+		start += 1
+	}
+	for i := 0; i < numThreads; i++ {
+		go getPrimes(start + uint64(i * 2), uint64(numThreads * 2))
+	}
+	for {
+		prime := <- ch
+		fmt.Printf("%d\n", prime)
+		w.WriteString(strconv.FormatUint(prime, 10) + "\n")
+	}
+}
+
+// coroutine that calculates primes and adds it to the channel
+func getPrimes(start, incr uint64) {
+	num := uint64(start)
+	for {
+		isPrime := true
+		if (num < 3 || num % 2 == 0) {
+			isPrime = false
+			num += incr
+			continue
+		}
+		var i uint64
+		for i = 3; i < num/2; i+=2 {
+			if num % i == 0 {
+				isPrime = false
+				break
+			}
+		}
+		if isPrime {
+			ch <- num
+		}
+		num += incr
+	}
+}