diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5dd141b..72386ae 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -10,14 +10,12 @@ if (${isBigEndian})
     add_definitions(-DWORDS_BIGENDIAN)
 endif()
 
-add_link_options("-lc")
-
 IF(CMAKE_SIZEOF_VOID_P EQUAL 8)
-    add_library(base16384 SHARED base1464.c)
-    add_library(base16384_s STATIC base1464.c)
+    add_library(base16384 SHARED file.c base1464.c)
+    add_library(base16384_s STATIC file.c base1464.c)
 ELSE()
-    add_library(base16384 SHARED base1432.c)
-    add_library(base16384_s STATIC base1432.c)
+    add_library(base16384 SHARED file.c base1432.c)
+    add_library(base16384_s STATIC file.c base1432.c)
 ENDIF()
 
 set_target_properties(base16384_b PROPERTIES OUTPUT_NAME base16384)
diff --git a/base1432.c b/base1432.c
index 44bed16..020f72e 100644
--- a/base1432.c
+++ b/base1432.c
@@ -61,7 +61,7 @@
 
 // #define DEBUG
 
-int encode(const char* data, int dlen, char* buf, int blen) {
+int base16384_encode(const char* data, int dlen, char* buf, int blen) {
 	int outlen = dlen / 7 * 8;
 	int offset = dlen % 7;
 	switch(offset) {	// 算上偏移标志字符占用的2字节
@@ -139,7 +139,7 @@ int encode(const char* data, int dlen, char* buf, int blen) {
 	return outlen;
 }
 
-int decode(const char* data, int dlen, char* buf, int blen) {
+int base16384_decode(const char* data, int dlen, char* buf, int blen) {
 	int outlen = dlen;
 	int offset = 0;
 	if(data[dlen-2] == '=') {
diff --git a/base1464.c b/base1464.c
index d96fbf8..517fc1b 100644
--- a/base1464.c
+++ b/base1464.c
@@ -61,7 +61,7 @@
 
 // #define DEBUG
 
-int encode(const char* data, int dlen, char* buf, int blen) {
+int base16384_encode(const char* data, int dlen, char* buf, int blen) {
 	int outlen = dlen / 7 * 8;
 	int offset = dlen % 7;
 	switch(offset) {	// 算上偏移标志字符占用的2字节
@@ -135,7 +135,7 @@ int encode(const char* data, int dlen, char* buf, int blen) {
 	return outlen;
 }
 
-int decode(const char* data, int dlen, char* buf, int blen) {
+int base16384_decode(const char* data, int dlen, char* buf, int blen) {
 	int outlen = dlen;
 	int offset = 0;
 	if(data[dlen-2] == '=') {
diff --git a/base16384.c b/base16384.c
index c811527..72e24bd 100644
--- a/base16384.c
+++ b/base16384.c
@@ -18,190 +18,13 @@
 #ifndef __cosmopolitan
 #include <stdio.h>
 #include <stdint.h>
-#include <stdlib.h>
-#include <sys/stat.h>
-#include <fcntl.h>
+#include <string.h>
 #include <time.h>
-#ifdef _WIN32
-	#include <windows.h>
-#else
-	#include <sys/mman.h>
-#endif
 #endif
 #include "base16384.h"
 
-#ifdef __cosmopolitan
-#define get_file_size(filepath) ((off_t)GetFileSize(filepath))
-#else
-static off_t get_file_size(const char* filepath) {
-    struct stat statbuf;
-    return stat(filepath, &statbuf)?-1:statbuf.st_size;
-}
-#endif
-
-char encbuf[BUFSIZ*1024/7*7];
-char decbuf[BUFSIZ*1024/8*8+2];
-
-static int encode_file(const char* input, const char* output) {
-	off_t inputsize;
-	FILE* fp = NULL;
-	FILE* fpo;
-	if(*(uint16_t*)input == *(uint16_t*)"-") { // read from stdin
-		inputsize = 0;
-		fp = stdin;
-	} else inputsize = get_file_size(input);
-	if(inputsize < 0) {
-		perror("Get file size error");
-		return 1;
-	}
-	fpo = (*(uint16_t*)output == *(uint16_t*)"-")?stdout:fopen(output, "wb");
-	if(!fpo) {
-		perror("Fopen output file error");
-		return 2;
-	}
-	if(!inputsize || inputsize > BUFSIZ*1024) { // stdin or big file, use encbuf & fread
-		inputsize = BUFSIZ*1024/7*7;
-		#ifdef _WIN32
-	}
-		#endif
-		if(!fp) fp = fopen(input, "rb");
-		if(!fp) {
-			perror("Fopen input file error");
-			return 3;
-		}
-
-		int outputsize = encode_len(inputsize)+16;
-		size_t cnt = 0;
-		fputc(0xFE, fpo);
-		fputc(0xFF, fpo);
-		while((cnt = fread(encbuf, sizeof(char), inputsize, fp))) {
-			int n = encode(encbuf, cnt, decbuf, outputsize);
-			if(fwrite(decbuf, n, 1, fpo) <= 0) {
-				perror("Write file error");
-				return 4;
-			}
-		}
-		/* 由操作系统负责释放资源
-			fclose(fpo);
-			fclose(fp);
-		以缩短程序运行时间 */
-	#ifndef _WIN32
-	} else { // small file, use mmap & fwrite
-		int fd = open(input, O_RDONLY);
-		if(fd <= 0) {
-			perror("Open input file error");
-			return 5;
-		}
-		char *input_file = mmap(NULL, (size_t)inputsize, PROT_READ, MAP_PRIVATE, fd, 0);
-		if(input_file == MAP_FAILED) {
-			perror("Map input file error");
-			return 6;
-		}
-		int outputsize = encode_len(inputsize)+16;
-		fputc(0xFE, fpo);
-		fputc(0xFF, fpo);
-		int n = encode(input_file, (int)inputsize, decbuf, outputsize);
-		if(fwrite(decbuf, n, 1, fpo) <= 0) {
-			perror("Write file error");
-			return 7;
-		}
-		munmap(input_file, (size_t)inputsize);
-		/* 由操作系统负责释放资源
-			fclose(fpo);
-			close(fd);
-		以缩短程序运行时间 */	
-	}
-	#endif
-	return 0;
-}
-
-#define rm_head(fp) {\
-	int ch = fgetc(fp);\
-	if(ch == 0xFE) fgetc(fp);\
-	else rewind(fp);\
-}
-
-#define skip_offset(input_file) ((input_file[0]==(char)0xFE)?2:0)
-
-static int is_next_end(FILE* fp) {
-	int ch = fgetc(fp);
-	if(ch == '=') return fgetc(fp);
-	ungetc(ch, fp);
-	return 0;
-}
-
-static int decode_file(const char* input, const char* output) {
-	off_t inputsize;
-	FILE* fp = NULL;
-	FILE* fpo;
-	if(*(uint16_t*)input == *(uint16_t*)"-") { // read from stdin
-		inputsize = 0;
-		fp = stdin;
-	} else inputsize = get_file_size(input);
-	if(inputsize < 0) {
-		perror("Get file size error");
-		return 1;
-	}
-	fpo = (*(uint16_t*)output == *(uint16_t*)"-")?stdout:fopen(output, "wb");
-	if(!fpo) {
-		perror("Fopen output file error");
-		return 2;
-	}
-	if(!inputsize || inputsize > BUFSIZ*1024) { // stdin or big file, use decbuf & fread
-		inputsize = BUFSIZ*1024/8*8;
-		#ifdef _WIN32
-	}
-		#endif
-		if(!fp) fp = fopen(input, "rb");
-		if(!fp) {
-			perror("Fopen input file error");
-			return 3;
-		}
-		int outputsize = decode_len(inputsize, 0)+16;
-		int cnt = 0;
-		int end = 0;
-		rm_head(fp);
-		while((cnt = fread(decbuf, sizeof(char), inputsize, fp))) {
-			if((end = is_next_end(fp))) {
-				decbuf[cnt++] = '=';
-				decbuf[cnt++] = end;
-			}
-			if(fwrite(encbuf, decode(decbuf, cnt, encbuf, outputsize), 1, fpo) <= 0) {
-				perror("Write file error");
-				return 4;
-			}
-		}
-		/* 由操作系统负责释放资源
-			fclose(fpo);
-			fclose(fp);
-		以缩短程序运行时间 */
-	#ifndef _WIN32
-	} else { // small file, use mmap & fwrite
-		int fd = open(input, O_RDONLY);
-		if(fd <= 0) {
-			perror("Open input file error");
-			return 5;
-		}
-		char *input_file = mmap(NULL, (size_t)inputsize, PROT_READ, MAP_PRIVATE, fd, 0);
-		if(input_file == MAP_FAILED) {
-			perror("Map input file error");
-			return 6;
-		}
-		int outputsize = decode_len(inputsize, 0)+16;
-		int off = skip_offset(input_file);
-		if(fwrite(encbuf, decode(input_file+off, inputsize-off, encbuf, outputsize), 1, fpo) <= 0) {
-			perror("Write file error");
-			return 7;
-		}
-		munmap(input_file, (size_t)inputsize);
-		/* 由操作系统负责释放资源
-			fclose(fpo);
-			close(fd);
-		以缩短程序运行时间 */	
-	}
-	#endif
-	return 0;
-}
+char encbuf[BASE16384_ENCBUFSZ];
+char decbuf[BASE16384_DECBUFSZ];
 
 #ifndef _WIN32
 unsigned long get_start_ms() {
@@ -211,32 +34,73 @@ unsigned long get_start_ms() {
 }
 #endif
 
+static void print_usage() {
+	puts("Copyright (c) 2022 Fumiama Minamoto.\nBase16384 2.2.0 (Oct 16th 2022). Usage:");
+	puts("base16384 [-edt] [inputfile] [outputfile]");
+	puts("  -e\t\tencode");
+	puts("  -d\t\tdecode");
+	puts("  -t\t\tshow spend time");
+	puts("  inputfile\tpass - to read from stdin");
+	puts("  outputfile\tpass - to write to stdout");
+}
+
 int main(int argc, char** argv) {
-	if(argc != 4) {
-        puts("Usage: -[e|d] <inputfile> <outputfile>");
-        puts("\t-e encode");
-        puts("\t-d decode");
-		puts("\t<inputfile>  pass - to read from stdin");
-		puts("\t<outputfile> pass - to write to stdout");
-        exit(EXIT_SUCCESS);
+	if(argc != 4 || argv[1][0] != '-') {
+		print_usage();
+        return -1;
     }
-	#ifdef _WIN32
-		clock_t t = clock();
-	#else
-		unsigned long t = get_start_ms();
-	#endif
-	int exitstat = 0;
-	switch(argv[1][1]) {
-		case 'e': exitstat = encode_file(argv[2], argv[3]); break;
-		case 'd': exitstat = decode_file(argv[2], argv[3]); break;
-		default: break;
+	int flaglen = strlen(argv[1]);
+	if(flaglen <= 1 || flaglen > 3) {
+		print_usage();
+        return -2;
 	}
-	if(!exitstat && *(uint16_t*)(argv[3]) != *(uint16_t*)"-") {
+	#ifdef _WIN32
+		clock_t t = 0;
+	#else
+		unsigned long t = 0;
+	#endif
+	base16384_err_t exitstat = base16384_err_ok;
+	char cmd = argv[1][1];
+	if(cmd == 't') {
+		if(flaglen == 2) {
+			print_usage(); return -3;
+		}
+		#ifdef _WIN32
+			t = clock();
+		#else
+			t = get_start_ms();
+		#endif
+		cmd = argv[1][2];
+	} else if(flaglen == 3) {
+		if(argv[1][2] != 't') {
+			print_usage(); return -4;
+		}
+		#ifdef _WIN32
+			t = clock();
+		#else
+			t = get_start_ms();
+		#endif
+	}
+	switch(cmd) {
+		case 'e': exitstat = base16384_encode_file(argv[2], argv[3], encbuf, decbuf); break;
+		case 'd': exitstat = base16384_decode_file(argv[2], argv[3], encbuf, decbuf); break;
+		default: print_usage(); return -5;
+	}
+	if(t && !exitstat && *(uint16_t*)(argv[3]) != *(uint16_t*)"-") {
 		#ifdef _WIN32
 			printf("spend time: %lums\n", clock() - t);
 		#else
 			printf("spend time: %lums\n", get_start_ms() - t);
 		#endif
 	}
+	if(exitstat) switch(exitstat) {
+		case base16384_err_get_file_size: perror("base16384_err_get_file_size"); break;
+		case base16384_err_fopen_output_file: perror("base16384_err_fopen_output_file"); break;
+		case base16384_err_fopen_input_file: perror("base16384_err_fopen_input_file"); break;
+		case base16384_err_write_file: perror("base16384_err_write_file"); break;
+		case base16384_err_open_input_file: perror("base16384_err_open_input_file"); break;
+		case base16384_err_map_input_file: perror("base16384_err_map_input_file"); break;
+		default: perror("base16384"); break;
+	}
     return exitstat;
 }
diff --git a/base16384.h b/base16384.h
index 2a4469c..5aa686b 100644
--- a/base16384.h
+++ b/base16384.h
@@ -1,5 +1,5 @@
-#ifndef _BASE14_H_
-#define _BASE14_H_
+#ifndef _BASE16384_H_
+#define _BASE16384_H_
 
 /* base16384.h
  * This file is part of the base16384 distribution (https://github.com/fumiama/base16384).
@@ -18,8 +18,26 @@
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
-// encode_len calc min buf size to fill encode result
-int encode_len(int dlen) {
+#include <stdint.h>
+
+// base16384_err_t is the return value of base16384_en/decode_file
+enum base16384_err_t {
+	base16384_err_ok,
+	base16384_err_get_file_size,
+	base16384_err_fopen_output_file,
+	base16384_err_fopen_input_file,
+	base16384_err_write_file,
+	base16384_err_open_input_file,
+	base16384_err_map_input_file,
+};
+// base16384_err_t is the return value of base16384_en/decode_file
+typedef enum base16384_err_t base16384_err_t;
+
+#define BASE16384_ENCBUFSZ (BUFSIZ*1024/7*7)
+#define BASE16384_DECBUFSZ (BUFSIZ*1024/8*8+2)
+
+// base16384_encode_len calc min buf size to fill encode result
+static inline int base16384_encode_len(int dlen) {
 	int outlen = dlen / 7 * 8;
 	int offset = dlen % 7;
 	switch(offset) {	// 算上偏移标志字符占用的2字节
@@ -35,8 +53,8 @@ int encode_len(int dlen) {
 	return outlen + 8;	// 冗余的8B用于可能的结尾的覆盖
 }
 
-// decode_len calc min buf size to fill decode result
-int decode_len(int dlen, int offset) {
+// base16384_decode_len calc min buf size to fill decode result
+static inline int base16384_decode_len(int dlen, int offset) {
 	int outlen = dlen;
 	switch(offset) {	// 算上偏移标志字符占用的2字节
 		case 0: break;
@@ -51,9 +69,20 @@ int decode_len(int dlen, int offset) {
 	return outlen / 8 * 7 + offset + 1; // 多出1字节用于循环覆盖
 }
 
-// encode data and write result into buf
-int encode(const char* data, int dlen, char* buf, int blen);
-// decode data and write result into buf
-int decode(const char* data, int dlen, char* buf, int blen);
+// base16384_encode encodes data and write result into buf
+int base16384_encode(const char* data, int dlen, char* buf, int blen);
 
-#endif
\ No newline at end of file
+// base16384_decode decodes data and write result into buf
+int base16384_decode(const char* data, int dlen, char* buf, int blen);
+
+// base16384_encode_file encodes input file to output file.
+//    use `-` to specify stdin/stdout
+//    encbuf & decbuf must be no less than BASE16384_ENCBUFSZ & BASE16384_DECBUFSZ
+base16384_err_t base16384_encode_file(const char* input, const char* output, char* encbuf, char* decbuf);
+
+// base16384_decode_file decodes input file to output file.
+//    use `-` to specify stdin/stdout
+//    encbuf & decbuf must be no less than BASE16384_ENCBUFSZ & BASE16384_DECBUFSZ
+base16384_err_t base16384_decode_file(const char* input, const char* output, char* encbuf, char* decbuf);
+
+#endif
diff --git a/file.c b/file.c
new file mode 100644
index 0000000..2d6fc4c
--- /dev/null
+++ b/file.c
@@ -0,0 +1,186 @@
+/* file.c
+ * This file is part of the base16384 distribution (https://github.com/fumiama/base16384).
+ * Copyright (c) 2022 Fumiama Minamoto.
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __cosmopolitan
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#ifdef _WIN32
+	#include <windows.h>
+#else
+	#include <sys/mman.h>
+#endif
+#endif
+#include "base16384.h"
+
+#ifdef __cosmopolitan
+#define get_file_size(filepath) ((off_t)GetFileSize(filepath))
+#else
+static off_t get_file_size(const char* filepath) {
+    struct stat statbuf;
+    return stat(filepath, &statbuf)?-1:statbuf.st_size;
+}
+#endif
+
+base16384_err_t base16384_encode_file(const char* input, const char* output, char* encbuf, char* decbuf) {
+	off_t inputsize;
+	FILE* fp = NULL;
+	FILE* fpo;
+	if(*(uint16_t*)input == *(uint16_t*)"-") { // read from stdin
+		inputsize = 0;
+		fp = stdin;
+	} else inputsize = get_file_size(input);
+	if(inputsize < 0) {
+		return base16384_err_get_file_size;
+	}
+	fpo = (*(uint16_t*)output == *(uint16_t*)"-")?stdout:fopen(output, "wb");
+	if(!fpo) {
+		return base16384_err_fopen_output_file;
+	}
+	if(!inputsize || inputsize > BUFSIZ*1024) { // stdin or big file, use encbuf & fread
+		inputsize = BUFSIZ*1024/7*7;
+		#ifdef _WIN32
+	}
+		#endif
+		if(!fp) fp = fopen(input, "rb");
+		if(!fp) {
+			return base16384_err_fopen_input_file;
+		}
+
+		int outputsize = base16384_encode_len(inputsize)+16;
+		size_t cnt = 0;
+		fputc(0xFE, fpo);
+		fputc(0xFF, fpo);
+		while((cnt = fread(encbuf, sizeof(char), inputsize, fp))) {
+			int n = base16384_encode(encbuf, cnt, decbuf, outputsize);
+			if(fwrite(decbuf, n, 1, fpo) <= 0) {
+				return base16384_err_write_file;
+			}
+		}
+		/* 由操作系统负责释放资源
+			fclose(fpo);
+			fclose(fp);
+		以缩短程序运行时间 */
+	#ifndef _WIN32
+	} else { // small file, use mmap & fwrite
+		int fd = open(input, O_RDONLY);
+		if(fd <= 0) {
+			return base16384_err_open_input_file;
+		}
+		char *input_file = mmap(NULL, (size_t)inputsize, PROT_READ, MAP_PRIVATE, fd, 0);
+		if(input_file == MAP_FAILED) {
+			return base16384_err_map_input_file;
+		}
+		int outputsize = base16384_encode_len(inputsize)+16;
+		fputc(0xFE, fpo);
+		fputc(0xFF, fpo);
+		int n = base16384_encode(input_file, (int)inputsize, decbuf, outputsize);
+		if(fwrite(decbuf, n, 1, fpo) <= 0) {
+			return base16384_err_write_file;
+		}
+		munmap(input_file, (size_t)inputsize);
+		/* 由操作系统负责释放资源
+			fclose(fpo);
+			close(fd);
+		以缩短程序运行时间 */	
+	}
+	#endif
+	return base16384_err_ok;
+}
+
+#define rm_head(fp) {\
+	int ch = fgetc(fp);\
+	if(ch == 0xFE) fgetc(fp);\
+	else rewind(fp);\
+}
+
+#define skip_offset(input_file) ((input_file[0]==(char)0xFE)?2:0)
+
+static int is_next_end(FILE* fp) {
+	int ch = fgetc(fp);
+	if(ch == '=') return fgetc(fp);
+	ungetc(ch, fp);
+	return 0;
+}
+
+base16384_err_t base16384_decode_file(const char* input, const char* output, char* encbuf, char* decbuf) {
+	off_t inputsize;
+	FILE* fp = NULL;
+	FILE* fpo;
+	if(*(uint16_t*)input == *(uint16_t*)"-") { // read from stdin
+		inputsize = 0;
+		fp = stdin;
+	} else inputsize = get_file_size(input);
+	if(inputsize < 0) {
+		return base16384_err_get_file_size;
+	}
+	fpo = (*(uint16_t*)output == *(uint16_t*)"-")?stdout:fopen(output, "wb");
+	if(!fpo) {
+		return base16384_err_fopen_output_file;
+	}
+	if(!inputsize || inputsize > BUFSIZ*1024) { // stdin or big file, use decbuf & fread
+		inputsize = BUFSIZ*1024/8*8;
+		#ifdef _WIN32
+	}
+		#endif
+		if(!fp) fp = fopen(input, "rb");
+		if(!fp) {
+			return base16384_err_fopen_input_file;
+		}
+		int outputsize = base16384_decode_len(inputsize, 0)+16;
+		int cnt = 0;
+		int end = 0;
+		rm_head(fp);
+		while((cnt = fread(decbuf, sizeof(char), inputsize, fp))) {
+			if((end = is_next_end(fp))) {
+				decbuf[cnt++] = '=';
+				decbuf[cnt++] = end;
+			}
+			if(fwrite(encbuf, base16384_decode(decbuf, cnt, encbuf, outputsize), 1, fpo) <= 0) {
+				return base16384_err_write_file;
+			}
+		}
+		/* 由操作系统负责释放资源
+			fclose(fpo);
+			fclose(fp);
+		以缩短程序运行时间 */
+	#ifndef _WIN32
+	} else { // small file, use mmap & fwrite
+		int fd = open(input, O_RDONLY);
+		if(fd <= 0) {
+			return base16384_err_open_input_file;
+		}
+		char *input_file = mmap(NULL, (size_t)inputsize, PROT_READ, MAP_PRIVATE, fd, 0);
+		if(input_file == MAP_FAILED) {
+			return base16384_err_map_input_file;
+		}
+		int outputsize = base16384_decode_len(inputsize, 0)+16;
+		int off = skip_offset(input_file);
+		if(fwrite(encbuf, base16384_decode(input_file+off, inputsize-off, encbuf, outputsize), 1, fpo) <= 0) {
+			return base16384_err_write_file;
+		}
+		munmap(input_file, (size_t)inputsize);
+		/* 由操作系统负责释放资源
+			fclose(fpo);
+			close(fd);
+		以缩短程序运行时间 */	
+	}
+	#endif
+	return base16384_err_ok;
+}