Add xorBlock for ARM architecture

[kartben]

Trying to cross compile for ARM, i got bitten by a missing implementation of the xorBlock function for ARM...

[kartben]

Actually, I think I don't really understand the need for an arch specific implementation of xorBlock? Is this for performance optimization? For disallowing xor's on blocks that are not aligned?
Isn't the "standard" xor implementation enough? https://golang.org/src/crypto/cipher/xor.go
Thanks!

/cc @jvermillard

[jacobsa]

There are arch-specific implementations because each contains arch-specific assumptions about the size of a block in relation to the size of uintptr.

crypto. fastXORWords is functionally equivalent but the support for variable-length slices may make it slower. I would want to see good benchmark results before switching to something similar. I specifically switched away from this strategy in 61fbfe1, but didn't record the results that caused me to do so.

Feel free to send a pull request for arm.

[ivajloip]

Pull request #5 tries to fix this issue.

[paralin]

As far as I can tell this all works perfectly on ARM today, maybe this can be closed?