It works very well at least on ARM. I've used MessagePack on iPhone 3GS for the format of a dictionary file (> 100MB). I utilized mmap and zero-copy deserializ

It works very well at least on ARM. I've used MessagePack on iPhone 3GS for the format of a dictionary file (> 100MB). I utilized mmap and zero-copy deserialization feature of MessagePack. And I received (and merged) some patches sent by those who use it on iPhone4/iPad2. I've never tried to run it on MIPS. But it probably works if you use gcc. (I'm author of MessagePack)