1 files changed, 92 insertions, 0 deletions
diff --git a/dataset/count.go b/dataset/count.go
new file mode 100644
index 0000000..b2e6d14
--- /dev/null
+++ b/dataset/count.go
@@ -0,0 +1,92 @@
+package dataset
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"os"
+	"runtime"
+	"sync/atomic"
+
+	"golang.org/x/sync/errgroup"
+)
+
+func countLinesAll(names []string, delimiter []byte) (int, error) {
+	g, ctx := errgroup.WithContext(context.Background())
+
+	g.SetLimit(runtime.NumCPU() - 1)
+
+	var total atomic.Int64
+
+	for _, name := range names {
+		g.Go(func() error {
+			select {
+			case <-ctx.Done():
+				return ctx.Err()
+			default:
+			}
+
+			var file *os.File
+
+			if f, err := os.Open(name); err != nil {
+				return err
+			} else {
+				file = f
+			}
+
+			if n, err := countLines(file, delimiter); err != nil {
+				return err
+			} else {
+				total.Add(n)
+			}
+
+			return nil
+		})
+	}
+
+	if err := g.Wait(); err != nil {
+		return 0, err
+	}
+
+	return int(total.Load()), nil
+}
+
+func countLines(r io.Reader, delimiter []byte) (int64, error) {
+	if len(delimiter) == 0 {
+		panic("empty delimiter")
+	}
+
+	l := len(delimiter)
+
+	buf := make([]byte, 128*1024)
+
+	var total int64
+
+	carry := 0
+
+	for {
+		n, err := r.Read(buf[carry:])
+
+		active := carry + n
+
+		if active >= l {
+			total += int64(bytes.Count(buf[:active], delimiter))
+
+			carry = l - 1
+
+			copy(buf[:carry], buf[active-carry:])
+		} else {
+			carry = active
+		}
+
+		if err == io.EOF {
+			break
+		}
+
+		if err != nil {
+			return 0, err
+		}
+	}
+
+	return total, nil
+}