NIOS2 HW & DIV Instructions + FPU

Unless something very obscure goes on, it is only the -custom-fpu-cfg option that forces single precision constants.

The C functions I found are the same horrid ones an arm system I used many years ago ended up using - they are very slow at the best of times [1].

For an embedded system you might get away with:

- No NaN, infinity or -0

- non-ieee rounding (maybe just truncate)

It is also a shame that altera didn't think through the custom instruction interface a little further.

- Separate opcode for FP

- Allow an instruction to disable interrupts before the following instruction. This would allow, for example, a 64bit result to be recovered.

[1] I spent a week or so writing them in arm asm - not that hard.