diff --git a/source/par2j/lib_opencl.c b/source/par2j/lib_opencl.c
index 0a57454..93e1394 100644
--- a/source/par2j/lib_opencl.c
+++ b/source/par2j/lib_opencl.c
@@ -1,5 +1,5 @@
 // lib_opencl.c
-// Copyright : 2022-01-15 Yutaka Sawada
+// Copyright : 2023-05-29 Yutaka Sawada
 // License : GPL
 
 #ifndef _WIN32_WINNT
@@ -317,7 +317,7 @@ int init_OpenCL(int unit_size, int *src_max, int *chunk_size)
 
 #ifdef DEBUG_OUTPUT
 			printf("MAX_COMPUTE_UNITS = %d\n", num_groups);
-			printf("MAX_WORK_GROUP_SIZE = %d\n", data_size);
+			printf("MAX_WORK_GROUP_SIZE = %zd\n", data_size);
 			printf("HOST_UNIFIED_MEMORY = %d\n", param_value);
 #endif
 			// MAX_COMPUTE_UNITS * MAX_WORK_GROUP_SIZE で計算力を測る、外付けGPUなら値を倍にする
@@ -436,7 +436,7 @@ int init_OpenCL(int unit_size, int *src_max, int *chunk_size)
 //		printf("4 KB cache (16-bytes * 256 work items), use if\n");
 #endif
 	} else {
-		OpenCL_method = 0;	// MMX用のコードは遅いので、キャッシュ最適化する必要が無い
+		OpenCL_method = 1;	// MMX用のコードは遅いので、キャッシュ最適化する必要が無い
 	}
 
 	// work group 数が必要以上に多い場合は減らす
@@ -466,7 +466,7 @@ int init_OpenCL(int unit_size, int *src_max, int *chunk_size)
 
 #ifdef DEBUG_OUTPUT
 	data_size = (size_t)unit_size * count;
-	printf("src buf : %d KB (%d blocks), possible\n", data_size >> 10, count);
+	printf("src buf : %zd KB (%d blocks), possible\n", data_size >> 10, count);
 #endif
 
 	// 出力先は1ブロック分だけあればいい
@@ -476,7 +476,7 @@ int init_OpenCL(int unit_size, int *src_max, int *chunk_size)
 	if (ret != CL_SUCCESS)
 		return (ret << 8) | 13;
 #ifdef DEBUG_OUTPUT
-	printf("dst buf : %d KB (%d Bytes), OK\n", data_size >> 10, data_size);
+	printf("dst buf : %zd KB (%zd Bytes), OK\n", data_size >> 10, data_size);
 #endif
 
 	// factor は最大個数分 (src_max個)
@@ -485,7 +485,7 @@ int init_OpenCL(int unit_size, int *src_max, int *chunk_size)
 	if (ret != CL_SUCCESS)
 		return (ret << 8) | 14;
 #ifdef DEBUG_OUTPUT
-	printf("factor buf : %d Bytes (%d factors), OK\n", data_size, (*src_max));
+	printf("factor buf : %zd Bytes (%d factors), OK\n", data_size, (*src_max));
 #endif
 
 /*
@@ -539,25 +539,33 @@ int init_OpenCL(int unit_size, int *src_max, int *chunk_size)
 	// Referred to "Embedding OpenCL Kernel Files in the Application on Windows"
 	res = FindResource(NULL, L"#1", L"RT_STRING");	// find the resource
 	if (res == NULL){
-		//printf("cannot find resource\n");
+#ifdef DEBUG_OUTPUT
+		printf("cannot find resource\n");
+#endif
 		return err;
 	}
 	glob = LoadResource(NULL, res);	// load the resource.
 	if (glob == NULL){
-		//printf("cannot load resource\n");
+#ifdef DEBUG_OUTPUT
+		printf("cannot load resource\n");
+#endif
 		return err;
 	}
 	p_source = (char *)LockResource(glob);	// lock the resource to get a char*
-	if (res == NULL){
-		//printf("cannot lock resource\n");
+	if (p_source == NULL){
+#ifdef DEBUG_OUTPUT
+		printf("cannot lock resource\n");
+#endif
 		return err;
 	}
 	data_size = SizeofResource(NULL, res);
 	if (data_size == 0){
-		//printf("cannot get size of resource\n");
+#ifdef DEBUG_OUTPUT
+		printf("cannot get size of resource\n");
+#endif
 		return err;
 	}
-	//printf("Source code length = %d characters\n", data_size);
+	//printf("OpenCL source code length = %zd characters\n", data_size);
 
 	// プログラムを作成する
 	program = fn_clCreateProgramWithSource(OpenCL_context, 1, (char **)&p_source, &data_size, &ret);
@@ -593,7 +601,7 @@ int init_OpenCL(int unit_size, int *src_max, int *chunk_size)
 	ret = fn_clGetKernelWorkGroupInfo(OpenCL_kernel, NULL, CL_KERNEL_WORK_GROUP_SIZE, sizeof(size_t), &data_size, NULL);
 	if ((ret == CL_SUCCESS) && (data_size < 256)){	// 最低でも 256以上は必要
 #ifdef DEBUG_OUTPUT
-		printf("KERNEL_WORK_GROUP_SIZE = %d\n", data_size);
+		printf("KERNEL_WORK_GROUP_SIZE = %zd\n", data_size);
 #endif
 		return (ret << 8) | 23;
 	}
@@ -622,7 +630,7 @@ int init_OpenCL(int unit_size, int *src_max, int *chunk_size)
 
 #ifdef DEBUG_OUTPUT
 	// ワークアイテム数
-	printf("\nMax number of work items = %d (256 * %d)\n", OpenCL_group_num * 256, OpenCL_group_num);
+	printf("\nMax number of work items = %zd (256 * %zd)\n", OpenCL_group_num * 256, OpenCL_group_num);
 #endif
 
 	return 0;
diff --git a/source/par2j/reedsolomon.c b/source/par2j/reedsolomon.c
index 63225ce..003ff06 100644
--- a/source/par2j/reedsolomon.c
+++ b/source/par2j/reedsolomon.c
@@ -1,5 +1,5 @@
 // reedsolomon.c
-// Copyright : 2022-10-08 Yutaka Sawada
+// Copyright : 2023-05-29 Yutaka Sawada
 // License : GPL
 
 #ifndef _UNICODE
@@ -28,6 +28,16 @@
 #include "reedsolomon.h"
 
 
+// GPU を使う最小データサイズ (MB 単位)
+// GPU の起動には時間がかかるので、データが小さすぎると逆に遅くなる
+#define GPU_DATA_LIMIT 512
+
+// GPU を使う最小ブロックサイズとブロック数
+// CPU と GPU で処理を割り振る為には、ある程度のブロック数を必要とする
+#define GPU_BLOCK_SIZE_LIMIT 65536
+#define GPU_SOURCE_COUNT_LIMIT 256
+#define GPU_PARITY_COUNT_LIMIT 32
+
 /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
 
 // chunk がキャッシュに収まるようにすれば速くなる！ (Cache Blocking という最適化手法)
@@ -554,8 +564,9 @@ unsigned int time_total = GetTickCount();
 #endif
 	// HDD なら 1-pass & Read some 方式を使う
 	// メモリー不足や SSD なら、Read all 方式でブロックを断片化させる
-	if ((OpenCL_method != 0) && (block_size >= 65536) && (source_num >= 256) && (parity_num >= 32) &&
-			((source_num + parity_num) * (__int64)block_size > 1048576 * 512)){
+	if ((OpenCL_method != 0) && (block_size >= GPU_BLOCK_SIZE_LIMIT) &&
+			(source_num >= GPU_SOURCE_COUNT_LIMIT) && (parity_num >= GPU_PARITY_COUNT_LIMIT) &&
+			((source_num + parity_num) * (__int64)block_size > 1048576 * GPU_DATA_LIMIT)){
 		// ブロック数が多いなら、ブロックごとにスレッドを割り当てる (GPU を使う)
 		err = -4;	// 2-pass & GPU read all
 	} else {
@@ -636,8 +647,9 @@ unsigned int time_total = GetTickCount();
 	if (err == 0){
 #endif
 	// メモリーが足りてる場合だけ 1-pass方式を使う
-	if ((OpenCL_method != 0) && (block_size >= 65536) && (source_num >= 256) && (parity_num >= 32) &&
-			((source_num + parity_num) * (__int64)block_size > 1048576 * 512)){
+	if ((OpenCL_method != 0) && (block_size >= GPU_BLOCK_SIZE_LIMIT) &&
+			(source_num >= GPU_SOURCE_COUNT_LIMIT) && (parity_num >= GPU_PARITY_COUNT_LIMIT) &&
+			((source_num + parity_num) * (__int64)block_size > 1048576 * GPU_DATA_LIMIT)){
 		err = -5;	// 1-pass & GPU read some
 	} else {
 		err = -3;	// 1-pass & Read some
@@ -764,8 +776,9 @@ time_matrix = GetTickCount() - time_matrix;
 	err = 0;	// IO method : 0=Auto, -2=Read all, -3=Read some, -4=GPU all, -5=GPU some
 	if (err == 0){
 #endif
-	if ((OpenCL_method != 0) && (block_size >= 65536) && (source_num >= 256) && (block_lost >= 32) &&
-			((source_num + block_lost) * (__int64)block_size > 1048576 * 512)){
+	if ((OpenCL_method != 0) && (block_size >= GPU_BLOCK_SIZE_LIMIT) &&
+			(source_num >= GPU_SOURCE_COUNT_LIMIT) && (block_lost >= GPU_PARITY_COUNT_LIMIT) &&
+			((source_num + block_lost) * (__int64)block_size > 1048576 * GPU_DATA_LIMIT)){
 		// ブロック数が多いなら、ブロックごとにスレッドを割り当てる (GPU を使う)
 		if (memory_use & 16){
 			err = -4;	// SSD なら Read all 方式でブロックが断片化しても速い
diff --git a/source/par2j/source.cl b/source/par2j/source.cl
index e057486..78aa92c 100644
--- a/source/par2j/source.cl
+++ b/source/par2j/source.cl
@@ -14,7 +14,7 @@ void calc_table(__local uint *mtab, int id, int factor)
 	mtab[id + 256] = sum;
 }
 
-__kernel void method0(
+__kernel void method1(
 	__global uint *src,
 	__global uint *dst,
 	__global ushort *factors,