Lesson 20 step 1, the timer

20-interrupts-timer/kernel/util.c

@@ -26,5 +26,22 @@ void int_to_ascii(int n, char str[]) {
     if (sign < 0) str[i++] = '-';
     str[i] = '\0';
 
-    /* TODO: implement "reverse" */
+    reverse(str);
+}
+
+/* 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;
 }

20-interrupts-timer/kernel/util.h

@@ -6,5 +6,7 @@
 void memory_copy(char *source, char *dest, int nbytes);
 void memory_set(u8 *dest, u8 val, u32 len);
 void int_to_ascii(int n, char str[]);
+void reverse(char s[]);
+int strlen(char s[]);
 
 #endif