bench: add Realistic (40% quoted) benchmark case (#86)

Add generateRealisticCSV / generateRealisticRecords generators and
BenchmarkReadAll_Realistic_100K_{Stdlib,SIMD} to cover the case where
prefixXOR / PCLMULQDQ fires on partial data — 4 of 10 fields quoted
with embedded commas, 6 plain. Also add BenchmarkReadAll_Quoted_100K
to provide a 100K-row baseline for the all-quoted worst case.

Author: nnnkkk7

benchmark_test.go

@@ -119,6 +119,50 @@ func BenchmarkReadAll_Quoted_10K_SIMD(b *testing.B) {
 	}
 }
 
+func BenchmarkReadAll_Quoted_100K_Stdlib(b *testing.B) {
+	data := generateQuotedCSV(100000, 10)
+	b.SetBytes(int64(len(data)))
+	for b.Loop() {
+		reader := csv.NewReader(bytes.NewReader(data))
+		reader.FieldsPerRecord = -1
+		_, _ = reader.ReadAll()
+	}
+}
+
+func BenchmarkReadAll_Quoted_100K_SIMD(b *testing.B) {
+	data := generateQuotedCSV(100000, 10)
+	b.SetBytes(int64(len(data)))
+	for b.Loop() {
+		reader := NewReader(bytes.NewReader(data))
+		reader.FieldsPerRecord = -1
+		_, _ = reader.ReadAll()
+	}
+}
+
+// =============================================================================
+// ReadAll Benchmarks - Realistic CSV (40% quoted)
+// =============================================================================
+
+func BenchmarkReadAll_Realistic_100K_Stdlib(b *testing.B) {
+	data := generateRealisticCSV(100000, 10)
+	b.SetBytes(int64(len(data)))
+	for b.Loop() {
+		reader := csv.NewReader(bytes.NewReader(data))
+		reader.FieldsPerRecord = -1
+		_, _ = reader.ReadAll()
+	}
+}
+
+func BenchmarkReadAll_Realistic_100K_SIMD(b *testing.B) {
+	data := generateRealisticCSV(100000, 10)
+	b.SetBytes(int64(len(data)))
+	for b.Loop() {
+		reader := NewReader(bytes.NewReader(data))
+		reader.FieldsPerRecord = -1
+		_, _ = reader.ReadAll()
+	}
+}
+
 // =============================================================================
 // ReadAll Benchmarks - Mixed CSV
 // =============================================================================

test_helpers_test.go

@@ -203,6 +203,19 @@ func generateEscapedQuotesCSV(numRows, numCols int) []byte {
 	return buf.Bytes()
 }
 
+// generateRealisticCSV generates CSV with 4/10 quoted fields containing commas (~40%).
+// Row template: "Alice, Smith",30,"Tokyo, JP",engineer,100,"Japan, Asia",active,42,"New York, US",2024
+// Cols 0,2,5,8 are quoted; this exercises the prefixXOR / PCLMULQDQ hot path
+// without the all-quoted overhead.
+func generateRealisticCSV(numRows, _ int) []byte {
+	var buf bytes.Buffer
+	for i := 0; i < numRows; i++ {
+		buf.WriteString(`"Alice, Smith",30,"Tokyo, JP",engineer,100,"Japan, Asia",active,42,"New York, US",2024`)
+		buf.WriteByte('\n')
+	}
+	return buf.Bytes()
+}
+
 // =============================================================================
 // Writer Benchmark Record Generators
 // =============================================================================
@@ -262,3 +275,18 @@ func generateEscapedQuotesRecords(numRows, numCols int) [][]string {
 	}
 	return records
 }
+
+// generateRealisticRecords returns records matching generateRealisticCSV.
+func generateRealisticRecords(numRows, _ int) [][]string {
+	template := []string{
+		"Alice, Smith", "30", "Tokyo, JP", "engineer",
+		"100", "Japan, Asia", "active", "42", "New York, US", "2024",
+	}
+	records := make([][]string, numRows)
+	for i := range records {
+		row := make([]string, len(template))
+		copy(row, template)
+		records[i] = row
+	}
+	return records
+}