From 806dcb7f2c01514275dab76116d494345ffb0fd0 Mon Sep 17 00:00:00 2001
From: Jonas Knobloch <jonas.knobloch@t-online.de>
Date: Thu, 30 Apr 2026 13:10:03 +0200
Subject: Return number of written shards

---
 llmc/cmd/data/fineweb.go |  2 +-
 llmc/tokenize.go         | 24 +++++++++++++-----------
 2 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/llmc/cmd/data/fineweb.go b/llmc/cmd/data/fineweb.go
index a1bf7df..599089d 100644
--- a/llmc/cmd/data/fineweb.go
+++ b/llmc/cmd/data/fineweb.go
@@ -37,7 +37,7 @@ func fineWeb() {
 
 	docs := llmc.TokenizeAll(reader, tokenizer, 50256)
 
-	if err := llmc.WriteShards(shelf.Abs("llmc/edu_fineweb100B"), "edu_fineweb", 100_000_000, docs); err != nil {
+	if _, err := llmc.WriteShards(shelf.Abs("llmc/edu_fineweb100B"), "edu_fineweb", 100_000_000, docs); err != nil {
 		log.Fatal(err)
 	}
 
diff --git a/llmc/tokenize.go b/llmc/tokenize.go
index 1863157..e90de58 100644
--- a/llmc/tokenize.go
+++ b/llmc/tokenize.go
@@ -34,38 +34,38 @@ func TokenizeAll(reader dataset.Reader, tok llm.Tokenizer, eot int) <-chan []uin
 	})
 }
 
-func WriteShards(path, name string, size int, docs <-chan []uint32) error {
+func WriteShards(path, name string, size int, docs <-chan []uint32) (int, error) {
 	if err := os.MkdirAll(path, os.ModePerm); err != nil {
-		return err
+		return 0, err
 	}
 
 	buffer := make([]uint32, 0, size)
 
-	shardIdx := 0
+	n := 0
 
 	flush := func() error {
 		split := "train"
 
-		if shardIdx == 0 {
+		if n == 0 {
 			split = "val"
 		}
 
-		shardName := filepath.Join(path, fmt.Sprintf("%s_%s_%06d.bin", name, split, shardIdx))
+		shardName := filepath.Join(path, fmt.Sprintf("%s_%s_%06d.bin", name, split, n))
 
 		d := DataFile[uint32]{
 			Model:  GPT2,
 			Tokens: buffer,
 		}
 
-		if n, err := Serialize(&d, shardName); err != nil {
+		if numTokens, err := Serialize(&d, shardName); err != nil {
 			return err
 		} else {
-			fmt.Printf("wrote %s (%d tokens)\n", filepath.Base(shardName), n)
+			fmt.Printf("wrote %s (%d tokens)\n", filepath.Base(shardName), numTokens)
 		}
 
 		buffer = buffer[:0]
 
-		shardIdx++
+		n++
 
 		return nil
 	}
@@ -85,14 +85,16 @@ func WriteShards(path, name string, size int, docs <-chan []uint32) error {
 			tokens = tokens[space:] // carry remainder
 
 			if err := flush(); err != nil {
-				return err
+				return n, err
 			}
 		}
 	}
 
 	if len(buffer) > 0 {
-		return flush()
+		if err := flush(); err != nil {
+			return n, err
+		}
 	}
 
-	return nil
+	return n, nil
 }
-- 
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