8080: Faster strlen; more multiplication optimizations

include/string.mfk

@@ -1,4 +1,16 @@
 
+#if ARCH_I80
+
+byte strzlen(pointer str) {
+    pointer end
+    end = str
+    while end[0] != 0 {
+        end += 1
+    }
+    return lo(end - str)
+}
+
+#else
 
 byte strzlen(pointer str) {
     byte index
@@ -7,4 +19,5 @@ byte strzlen(pointer str) {
         index += 1
     }
     return index
-}
+}
+#endif