initial commit

Author: Alex Kahn

go.mod

@@ -0,0 +1,3 @@
+module github.com/akahn/lottery
+
+go 1.19

go.sum

@@ -0,0 +1,101 @@
+package main
+
+import (
+	"encoding/binary"
+	"encoding/hex"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"runtime"
+	"runtime/pprof"
+	"sync"
+	"sync/atomic"
+	"time"
+)
+
+var start = flag.Int64("start", 0, "start timestamp")
+var end = flag.Int64("end", time.Now().Unix(), "end timestamp")
+
+func main() {
+	flag.Parse()
+
+	// TODO: Investigate the suspiciously round numbers
+	beginRange := *start
+	endRange := *end
+	span := endRange - beginRange
+
+	cores := runtime.NumCPU()
+	chunkSize := int64(float64(span) / float64(cores))
+	log.Printf("Dividing %d (%d–%d) timestamps into %d chunks of size %d", span, beginRange, endRange, cores, chunkSize)
+
+	if profile, _ := os.LookupEnv("PROFILE"); profile != "" {
+		filename := fmt.Sprintf("profile_%d-%d.pprof", beginRange, endRange)
+		f, err := os.Create(filename)
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		pprof.StartCPUProfile(f)
+		defer pprof.StopCPUProfile()
+	}
+
+	wg := sync.WaitGroup{}
+	count := atomic.Int64{}
+
+	for i := 0; i < cores; i += 1 {
+		wg.Add(1)
+		start := beginRange + (int64(i) * chunkSize)
+		end := start + chunkSize - 1
+		log.Printf("Spawning goroutine %d from %d to %d (chunk size %d)", i, start, end, chunkSize)
+		go scanRange(i, start, end, &count, &wg)
+	}
+
+	wg.Wait()
+	total := count.Load()
+	log.Printf("Total: %d/%d (%f)", total, span, float64(total)/float64(span))
+}
+
+func scanRange(id int, start int64, end int64, count *atomic.Int64, wg *sync.WaitGroup) {
+	timestamp := uint32(start)
+
+	numericalCount := 0
+	passes := 0
+
+	var b [4]byte
+	for {
+		if timestamp >= uint32(end) {
+			log.Printf("Goroutine %d reached the end (%d). Found numerical hexes in %d/%d (%f) passes.", id, timestamp, numericalCount, passes, float64(numericalCount)/float64(passes))
+			count.Add(int64(numericalCount))
+			wg.Done()
+			return
+		}
+
+		binary.BigEndian.PutUint32(b[0:4], timestamp)
+		// TODO: Reduce allocations by replacing EncodeToString with Encode
+		hex := hex.EncodeToString(b[:])
+
+		if containsLetter([]byte(hex)) {
+			// Found an alphabetical character, skip this ID altogether
+			passes += 1
+			timestamp += 1
+			continue
+		}
+
+		// No alphabetical characters encountered
+		//fmt.Printf("%s %d\n", hex, timestamp)
+		numericalCount += 1
+		passes += 1
+		timestamp += 1
+	}
+}
+
+func containsLetter(id []byte) bool {
+	for _, ch := range id {
+		if ch >= 97 && ch <= 122 {
+			return true
+		}
+	}
+
+	return false
+}