Playing with Go

primes.go

@@ -0,0 +1,69 @@
+package main
+
+import (
+	"container/heap"
+	"fmt"
+)
+
+type sieve struct {
+	next int
+	ch   chan int
+}
+
+type intHeap []sieve
+
+func (h intHeap) Len() int           { return len(h) }
+func (h intHeap) Less(i, j int) bool { return h[i].next < h[j].next }
+func (h intHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
+
+func (h *intHeap) Push(x interface{}) { *h = append(*h, x.(sieve)) }
+
+func (h *intHeap) Pop() interface{} {
+	defer func() { *h = (*h)[0 : h.Len()-1] }()
+	return (*h)[h.Len()-1]
+}
+
+func makeSieve(ch chan int, prime int) sieve {
+	counter := make(chan int, 1)
+	count := prime
+	go func() {
+		count += prime
+		counter <- count
+	}()
+	ch <- prime
+	return sieve{<-counter, counter}
+}
+
+func primes(ch chan int) {
+	h := intHeap{makeSieve(ch, 2), makeSieve(ch, 3)}
+	heap.Init(&h)
+	c := h[0].next
+	for {
+		if c != h[0].next {
+			heap.Push(&h, makeSieve(ch, c))
+		}
+		c = h[0].next
+		for c == h[0].next {
+			_N := heap.Pop(&h)
+			n := _N.(sieve)
+			c = n.next
+			heap.Push(&h, sieve{<-n.ch, n.ch})
+		}
+		c++
+	}
+}
+
+func main() {
+	ch := make(chan int, 1)
+	go primes(ch)
+	fmt.Printf("%d\n", <-ch)
+	fmt.Printf("%d\n", <-ch)
+	fmt.Printf("%d\n", <-ch)
+	for <-ch < (1 << 16) {
+	}
+	fmt.Printf("%d\n", 1<<16)
+	fmt.Printf("%d\n", <-ch)
+	fmt.Printf("%d\n", 1<<17)
+	for {
+	}
+}