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Currently, full-screen Web applications fail to use the Nitro acceleration Apple added to iOS 4.3. This can result in Web applications designed for the iPhone running much slower when saved to a home screen than they would if launched directly through the Mobile Safari browser.
The fix was revealed by user "Xuzz" at Hacker News, who said that revealing the information was "probably" breaking their non-disclosure agreement with Apple. "Web.app now has the 'dynamic codesigning' entitlement, which enables Nitro," they said.
In a follow-up question, the user was asked about UIWebViews, which do not currently have Nitro benefits. "Xuzz" said that has not been added in iOS 5, but it's a security restriction.
"They can't give dynamic-codesigning to all apps, or their security (which taht disables, as a requirement to enable the JIT) would then be useless," they said.
SunSpider benchmark tests conducted earlier this year found that the Safari browser on the iPhone would run through code in 4.2 seconds. But a full-screen Web application saved to an iOS home screen would take more than twice as long — 10.2 seconds — to complete.
That's because full-screen Web applications, and native applications using UIWebView, use a different engine from Safari — an internal process called WebSheet.app.