site_url & base_url performance

hey,
while optimizing my application I noticed that site_url & base_url are very slow. So caching the base_url improved my menu generation speed by 95%. All tests with 100 request & 24 calls

• site_url( $URI ) : 21ms
  
• site_url().$URI : 20ms
  
• base_url( $URI ) : 8.8ms
  
• base_url().$URI : 3.5ms
  
• single base_url() call : 0.2ms
  
• single site_url() call : 1.0ms
  

So maybe we can add an cache mechanic to these functions ?