From 27b131c982f63ebcce301d9ada755fb814dd3e34 Mon Sep 17 00:00:00 2001
From: "Peter J. Holzer" <hjp@hjp.at>
Date: Mon, 12 Jul 2021 19:40:34 +0200
Subject: [PATCH] Compute and print primes (non-parallel)

This is already a slightly optimized version: I hardcode 2 and compute
only odd primes and I skip multiples of lesser primes in the inner loop.
This roughly matches the algorithm used by Dave Plummer in his Youtube
series. Just to have the same baseline
---
 eratosthenes_parallel.go | 44 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)
 create mode 100644 eratosthenes_parallel.go

diff --git a/eratosthenes_parallel.go b/eratosthenes_parallel.go
new file mode 100644
index 0000000..6058388
--- /dev/null
+++ b/eratosthenes_parallel.go
@@ -0,0 +1,44 @@
+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([]bool, n)
+	col := 0
+	var found int64
+	var i int64
+	i = 2
+	found++
+	s := fmt.Sprintf("%d, ", i)
+	fmt.Print(s)
+	col += len(s)
+	for i = 3; i < n; i += 2 {
+		if !sieve[i] {
+			found++
+			s := fmt.Sprintf("%d, ", i)
+			if col+len(s) > 80 {
+				fmt.Print("\n")
+				col = 0
+			}
+			fmt.Print(s)
+			col += len(s)
+			for j := i * i; j < n; j += 2 * i {
+				sieve[j] = true
+			}
+		}
+	}
+	d := time.Since(t0)
+	fmt.Println()
+	fmt.Println(found, "primes found in", d)
+
+}