diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..434b9d5
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,14 @@
+PROG=csum
+OBJS=calc_checksum.o
+
+$(PROG): $(OBJS)
+	mkdir bin
+	$(CC) -o $@ $^
+	mv $@ bin
+
+.c.o:
+	gcc -c $<
+
+.PHONY: clean
+clean:
+	rm -fr bin $(OBJS)
diff --git a/calc_checksum.c b/calc_checksum.c
new file mode 100644
index 0000000..a616d66
--- /dev/null
+++ b/calc_checksum.c
@@ -0,0 +1,141 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static int ENABLE_DEBUG = 0;
+#define DEBUG
+#define DEBUG_BEGIN\
+    if(ENABLE_DEBUG) do {
+#define DEBUG_END\
+    } while(0);
+
+#define NUMS_LEN 100
+
+uint8_t calc_sum(uint32_t a, int32_t b, int32_t c, int32_t d, int32_t e);
+
+// Reserve function
+uint8_t calc_sum2(uint32_t a, int32_t* b, int b_len);
+uint8_t sum_uint32(uint32_t* a, int len, uint8_t sum);
+uint8_t sum_int32(int32_t* a, int len, uint8_t sum);
+
+
+int main(int argc, char *argv[]) {
+    float nums[NUMS_LEN] = {0.0};
+    int i, nums_count = 0;
+    int num_start = 0;
+    int num_begin = 0;
+
+    
+    if (argc <= 1) {
+        printf("using: %s [--debug | -d] num1,num2,...\n", argv[0]); return 0;
+    }
+    if(!strcmp(argv[1], "--debug") || !strcmp(argv[1], "-d")) {
+	ENABLE_DEBUG = 1, num_begin = 2;
+	if (argc <= 2) {
+	    printf("using: %s [--debug | -d] num1,num2,...\n", argv[0]); return 0;
+	}
+    }
+    // parse args to nums
+    for (i = 0; argv[num_begin][i] != '\0'; i++) {
+        if(argv[num_begin][i] == ',') {
+	    // store
+	    argv[num_begin][i] = '\0';
+	    nums[nums_count] = (float)atof((const char*)&argv[num_begin][num_start]);
+
+	    // update
+            nums_count++;
+	    num_start = i+1;
+	}
+    }
+    // store
+    argv[num_begin][i] = '\0';
+    nums[nums_count] = (float)atof(&argv[num_begin][num_start]);
+    
+    // update
+    nums_count++;
+    num_start = i+1;
+
+    // dump
+    DEBUG_BEGIN
+        printf("args = [");
+        for (i = 0; i < nums_count; i++) {
+            printf(" %f, ", nums[i]);
+        }
+        printf("]\n");
+    DEBUG_END
+    {
+        uint8_t sum = calc_sum((uint32_t)nums[0],(int32_t)nums[1],(int32_t)nums[2],(int32_t)nums[3],(int32_t)nums[4]);
+        printf("check sum = %u\n", sum);
+    }
+    DEBUG_BEGIN
+        {
+            int32_t a[4] = { (int32_t)nums[1],(int32_t)nums[2],(int32_t)nums[3],(int32_t)nums[4] };
+            uint8_t sum = calc_sum2(nums[0],a,4);
+            printf("check2 sum = %u\n", sum);
+        }
+    DEBUG_END
+}
+
+uint8_t calc_sum(uint32_t a, int32_t b, int32_t c, int32_t d, int32_t e)
+{
+    union {
+        uint32_t u32;
+        uint8_t  u8[4];
+    } x;
+    union {
+        int32_t u32;
+        uint8_t u8[4];
+    } y;
+
+    uint8_t rv;
+    DEBUG_BEGIN
+        printf("a = %u, b = %d, c = %d, d = %d, e = %d\n", a,b,c,d,e);
+    DEBUG_END
+    x.u32 =a;
+    y.u32 =b;
+    rv= x.u8[0]+x.u8[1]+x.u8[2]+x.u8[3]+y.u8[0]+y.u8[1]+y.u8[2]+y.u8[3];
+    y.u32 =c;
+    rv += y.u8[0]+y.u8[1]+y.u8[2]+y.u8[3];
+    y.u32 =d;
+    rv += y.u8[0]+y.u8[1]+y.u8[2]+y.u8[3];
+    y.u32 =e;
+    rv += y.u8[0]+y.u8[1]+y.u8[2]+y.u8[3];
+    return rv;
+}
+
+uint8_t calc_sum2(uint32_t a, int32_t* b, int b_len)
+{
+    uint8_t rv = 0;
+
+    rv = sum_uint32(&a, 1, rv);
+    rv = sum_int32(b, b_len, rv);
+
+    return rv;
+}
+uint8_t sum_uint32(uint32_t* a, int len, uint8_t sum)
+{
+    union {
+        uint32_t u32;
+        uint8_t  u8[4];
+    } val;
+
+    int next = len-1;
+    if (next < 0) return sum;
+    val.u32 = a[next];
+    sum += val.u8[0]+val.u8[1]+val.u8[2]+val.u8[3];
+    return sum_uint32(a, next, sum);
+}
+
+uint8_t sum_int32(int32_t* a, int len, uint8_t sum)
+{
+    union {
+        int32_t  d32;
+        uint8_t  u8[4];
+    } val;
+
+    int next = len-1;
+    if (next < 0) return sum;
+    val.d32 = a[next];
+    sum += val.u8[0]+val.u8[1]+val.u8[2]+val.u8[3];
+    return sum_uint32(a, next, sum);
+}