add testing suite for length difference function

Makefile

@@ -2,6 +2,14 @@ CFLAGS=-O3 -Iinc/
 
 build: main
 
+test: tester
+
+tester: out/tester.o out/swapper.o
+	gcc $(CFLAGS) out/tester.o out/swapper.o -o tester
+
+out/tester.o: out/ src/tester.c
+	gcc $(CFLAGS) -c src/tester.c -o out/tester.o
+
 out/:
 	mkdir out/
 
@@ -15,6 +23,6 @@ out/swapper.o: out/ src/swapper.c
 	gcc $(CFLAGS) -c src/swapper.c -o out/swapper.o
 
 clean:
-	rm -r main out/
+	rm -r main tester out/
 
-.PHONY: build clean
+.PHONY: build test clean

src/tester.c

@@ -0,0 +1,148 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include "swapper.h"
+
+enum read_state {
+    LEN = 0,
+    STR1 = 1,
+    STR2 = 2,
+    FINISH = 3,
+    IMPOSSIBLE_STATE = 4
+};
+
+static int to_int(char *a)
+{
+    int value = 0;
+
+    for (int i = 0; i < 4; i++) {
+        if (a[i] == '\0')
+            break;
+
+        value *= 10;
+        value += (int) a[i] - (int) '0';
+    }
+
+    return value;
+}
+
+static void inplace_memcpy(char *buf, int offset)
+{
+    for (int i = 0; i < 1024 - offset; i++)
+        buf[i] = buf[offset+i];
+}
+
+static int read_more(int f, char *buf, int bytes_read)
+{
+    // in-place memcpy
+    inplace_memcpy(buf, bytes_read);
+
+    // reading more data
+    int new_bytes = read(f, &(buf[1024 - bytes_read]), bytes_read);
+
+    // returning current amount of bytes in buffer
+    return 1024 - bytes_read + new_bytes;
+}
+
+static int parse_case(char *cmd, int *target_length_diff, char *str_a, char *str_b)
+{
+    int bytes_read;
+    int write_offset = 0;
+    char len_buffer[4] = {0};
+    enum read_state rs = LEN;
+
+    for (bytes_read = 0; bytes_read < 1024; bytes_read++) {
+        switch (cmd[bytes_read]) {
+        case ' ':
+            switch (rs) {
+            case LEN:
+                *target_length_diff = to_int(len_buffer);
+                break;
+            case STR1:
+                str_a[write_offset] = '\0';
+                break;
+            }
+            rs++;
+            write_offset = 0;
+            break;
+
+        case '\n':
+            str_b[write_offset] = '\0';
+            bytes_read++;
+            goto finish;
+            break;
+
+        default:
+            switch(rs) {
+            case LEN:
+                len_buffer[write_offset] = cmd[bytes_read];
+                break;
+            case STR1:
+                str_a[write_offset] = cmd[bytes_read];
+                break;
+            case STR2:
+                str_b[write_offset] = cmd[bytes_read];
+                break;
+            }
+            write_offset++;
+            break;
+        }
+    }
+
+    finish:
+    return bytes_read;
+}
+
+static int assert_length(int test_id, int target_length_diff, char *a, char *b)
+{
+    int len_diff = swapper_length_difference(a, b);
+
+    if (len_diff == target_length_diff) {
+        printf("[TEST#%02d] OK\r", test_id);
+        return 0;
+    } else {
+        printf("\n[TEST#%02d] FAILED!\n", test_id);
+        printf("Case details:\n");
+        printf("Str1: %s\n", a);
+        printf("Str2: %s\n", b);
+        printf("Mismatch: %d expected, %d retrieved\n", target_length_diff, len_diff);
+        return 1;
+    }
+}
+
+
+int main(void)
+{
+    int success_tests_counter = 0;
+    int failed_tests_counter = 0;
+
+    int f = open("test/testcases_len", O_RDONLY);
+
+    if (f < 0)
+        return 1;
+
+    char cmd[1024];
+    int remaining_buffer_length;
+    remaining_buffer_length = read(f, cmd, 1024);
+
+    while (remaining_buffer_length) {
+        char str_a[1024], str_b[1024];
+        int target_length_diff;
+
+        int bytes_read = parse_case(cmd, &target_length_diff, str_a, str_b);
+        
+        if (assert_length(success_tests_counter + failed_tests_counter + 1, target_length_diff, str_a, str_b))
+            failed_tests_counter++;
+        else
+            success_tests_counter++;
+
+        if (remaining_buffer_length == 1024)
+            remaining_buffer_length = read_more(f, cmd, bytes_read);
+        else
+            inplace_memcpy(cmd, bytes_read);
+            remaining_buffer_length -= bytes_read;
+    }
+
+    printf("\nSummary: %d passed, %d failed\n", success_tests_counter, failed_tests_counter);
+    close(f);
+}

test/testcases_len

@@ -0,0 +1,5 @@
+2 wert tr
+6 12345678 12
+0 1234 1234
+3 1 123
+6 12 88888888