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My understanding of the hardware on the iPhone is that there IS an FPU. It is only enabled when NOT compiled Thumb. Is this understanding correct?

More specifically, is code compiled under MonoTouch taking advantage of the FPU?

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up vote 4 down vote accepted

The MonoTouch v3 AOT compiler and runtime are both compiled in armv6 mode, and take full advantage of the VFP.

As for FPU support in thumb, the original thumb instruction set, which is present on the iPhone 2G and iPhone 3G only has support for Thumb, which as you stated does not have support for accessing the VFP or NEON registers.

All of the iOS hardware since the iPhone 3GS supports Thumb2 which does have support for accessing VFP and NEON registers, and the upcoming MonoTouch v4 which will have support for limiting the output to those devices will take full advantage of this as well.

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