Tweaks to maths routines

[petermcs]

Mostly R6K improvements to speed things up by using new instructions and careful alignment. Some instructions changed from 1 byte instruction to two byte equivelant to maximise the run of aligned instructions which improves things for 16 bit memory. Modified division to bail out early in 8 bit steps to reduce number of loops required. Added unsigned 64 by 32 division and lower overhead shifts to support porting of Mbed TLS

[tomlogic]

Did you write any test programs to validate this code, with coverage for multiple cases? If you've been using it extensively in your software and updated TLS code, it's probably safe to merge. But there would be some benefit to ensuring edge cases still give the expected answer.

If you have test code, can you add it as sample programs? I'm even open to having a Samples/Test directory with test programs to validate various functions.

[tomlogic]

I realize the original code used the @pc+x notation, but seeing it here feels risky -- it depends on knowing exactly how many opcodes show up in following statements. Is there a reason we can't just replace the jr destinations with local labels?

[petermcs]

Done, replaced in the new code and the old code. There is one instance left in a macro but there is no easy way to handle those

[tomlogic]

As in my other reviews, I'd like to see at least a short comment on these align statements that we're targeting even alignment for improved performance on 5000/6000 with 16-bit memory.

[petermcs]

Done

[petermcs]

Did you write any test programs to validate this code, with coverage for multiple cases? If you've been using it extensively in your software and updated TLS code, it's probably safe to merge. But there would be some benefit to ensuring edge cases still give the expected answer.

If you have test code, can you add it as sample programs? I'm even open to having a Samples/Test directory with test programs to validate various functions.

I did have some test code when I was doing the development but didn't hold on to it. It has been used extensively and the Mbed TLS test code which I've run a lot is very sensitive to any errors...

[tomlogic]

I'm finally getting around to reviewing your PRs and merging them. Do you have any stats on the improvement you saw with the new code? Or was the change primarily to support the addition of G_div_ll_l()?

[petermcs]

I'm finally getting around to reviewing your PRs and merging them. Do you have any stats on the improvement you saw with the new code? Or was the change primarily to support the addition of G_div_ll_l()?

Thanks for that Tom.

I don't have any stats but from memory they were small improvements and would have shaved a few milliseconds of some of the mbedtls test run times - nothing dramatic but with the amount of processing the TLS stuff requires, every little bit helps! Since I started the mbedtls port I've managed to improve the test run times to the point where they are a quarter of the original but when one test case takes 27 seconds to run in the first place, getting it down to 7 seconds still leaves a bit to be desired...