perf(chunk): Use min instead branch

Author: Vildan Safin

benchmark/core_slice_bench_test.go

@@ -1013,3 +1013,91 @@ func BenchmarkFromSlicePtrOr(b *testing.B) {
 		})
 	}
 }
+
+func BenchmarkChunkIntSmallDataSmallChunk(b *testing.B) {
+	data := make([]int, 100)
+	for i := range data {
+		data[i] = i
+	}
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = lo.Chunk(data, 3)
+	}
+}
+
+func BenchmarkChunkIntSmallDataLargeChunk(b *testing.B) {
+	data := make([]int, 100)
+	for i := range data {
+		data[i] = i
+	}
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = lo.Chunk(data, 50)
+	}
+}
+
+func BenchmarkChunkIntMediumDataSmallChunk(b *testing.B) {
+	data := make([]int, 10_000)
+	for i := range data {
+		data[i] = i
+	}
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = lo.Chunk(data, 7)
+	}
+}
+
+func BenchmarkChunkIntMediumDataLargeChunk(b *testing.B) {
+	data := make([]int, 10_000)
+	for i := range data {
+		data[i] = i
+	}
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = lo.Chunk(data, 1024)
+	}
+}
+
+func BenchmarkChunkIntLargeDataSmallChunk(b *testing.B) {
+	data := make([]int, 1_000_000)
+	for i := range data {
+		data[i] = i
+	}
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = lo.Chunk(data, 13)
+	}
+}
+
+func BenchmarkChunkIntLargeDataLargeChunk(b *testing.B) {
+	data := make([]int, 1_000_000)
+	for i := range data {
+		data[i] = i
+	}
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = lo.Chunk(data, 8192)
+	}
+}
+
+func BenchmarkChunkStringMediumDataSmallChunk(b *testing.B) {
+	data := make([]string, 10_000)
+	for i := range data {
+		data[i] = "some string"
+	}
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = lo.Chunk(data, 7)
+	}
+}
+
+func BenchmarkChunkStringMediumDataLargeChunk(b *testing.B) {
+	data := make([]string, 10_000)
+	for i := range data {
+		data[i] = "some string"
+	}
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = lo.Chunk(data, 1024)
+	}
+}

slice.go

@@ -357,24 +357,28 @@ func Chunk[T any, Slice ~[]T](collection Slice, size int) []Slice {
 	}
 
 	chunksNum := len(collection) / size
+	extraChunk := 0
 	if len(collection)%size != 0 {
-		chunksNum++
+		extraChunk++
 	}
 
-	result := make([]Slice, 0, chunksNum)
-
-	for i := 0; i < chunksNum; i++ {
-		last := (i + 1) * size
-		if last > len(collection) {
-			last = len(collection)
-		}
+	result := make([]Slice, 0, chunksNum+extraChunk)
 
+	i := 0
+	for ; i < chunksNum; i++ {
 		// Copy chunk in a new slice, to prevent memory leak and free memory from initial collection.
-		newSlice := make(Slice, last-i*size)
-		copy(newSlice, collection[i*size:last])
+		newSlice := make(Slice, size)
+		copy(newSlice, collection[i*size:(i+1)*size])
 		result = append(result, newSlice)
 	}
 
+	if extraChunk > 0 {
+		lastStart := i * size
+		lastChunk := make(Slice, len(collection)-lastStart)
+		copy(lastChunk, collection[lastStart:])
+		result = append(result, lastChunk)
+	}
+
 	return result
 }