klibc: add string related func

core/klibc.c

@@ -55,3 +55,35 @@ char * itoa( int value, char * str, int base )
     }
     return rc;
 }
+
+/* K&R */
+void reverse(char s[])
+{
+    int c, i, j;
+    for (i = 0, j = strlen(s) - 1; i < j; i++, j--) {
+        c    = s[i];
+        s[i] = s[j];
+        s[j] = c;
+    }
+}
+
+/* K&R */
+int strlen(char s[])
+{
+    int i = 0;
+    while (s[i] != '\0')
+        ++i;
+    return i;
+}
+
+/* K&R
+ * Returns <0 if s1<s2, 0 if s1==s2, >0 if s1>s2 */
+int strcmp(char s1[], char s2[])
+{
+    int i;
+    for (i = 0; s1[i] == s2[i]; i++) {
+        if (s1[i] == '\0')
+            return 0;
+    }
+    return s1[i] - s2[i];
+}

core/klibc.h

@@ -4,3 +4,6 @@
 void *memcpy(void *dest, const void *src, size_t n);
 void *memset(void *s, int c, size_t n);
 char *itoa(int value, char *str, int base);
+void reverse(char s[]);
+int strlen(char s[]);
+int strcmp(char s1[], char s2[]);