add basic code

inc/swapper.h

@@ -0,0 +1,9 @@
+#ifndef __SWAPPER_HEADER
+#define __SWAPPER_HEADER
+
+#define __SWAPPER_MAX_STR_LENGTH 65535
+
+int swapper_length_difference(char *, char *);
+void swapper_swap(char *, char *);
+
+#endif

src/main.c

@@ -0,0 +1,17 @@
+#include <stdio.h>
+#include "swapper.h"
+
+int main(int argc, char **argv)
+{
+    if (3 != argc)
+        return 1;
+
+    if (swapper_length_difference(argv[1], argv[2]))
+        return 2;
+
+    swapper_swap(argv[1], argv[2]);
+
+    printf("%s\n%s\n", argv[1], argv[2]);
+
+    return 0;
+}

src/swapper.c

@@ -0,0 +1,48 @@
+#include <stdio.h>
+#include "swapper.h"
+
+#define ABS(val) ( (val) >= 0 ? (val) : -(val) )
+#define ALIGN8(val) ( (((val) >> 3) << 3) )
+
+union tmp {
+    long int l;
+    char c;
+};
+
+static int strlen_c(char *a)
+{
+    int len;
+
+    for (len = 0; len < __SWAPPER_MAX_STR_LENGTH; len++) {
+        if (a[len] == '\0')
+            break;
+    }
+
+    return len;
+}
+
+int swapper_length_difference(char *a, char *b)
+{
+    int len_a = strlen_c(a);
+    int len_b = strlen_c(b);
+
+    return ABS(len_a - len_b);
+}
+
+void swapper_swap(char *a, char *b) {
+    int len = strlen_c(a);
+
+    union tmp t;
+
+    for (int i = 0; i < (len >> 3); i++) {
+        t.l = ((long int*) a)[i];
+        ((long int*) a)[i] = ((long int*) b)[i];
+        ((long int*) b)[i] = t.l;
+    }
+
+    for (int i = ALIGN8(len); i < len; i++) {
+        t.c = a[i];
+        a[i] = b[i];
+        b[i] = t.c;
+    }
+}