Re: Is it safe to index a little bit out of bounds

If you are looking for ascii (or non-ascii characters) in a byte array, you build a word-sized mask like 0b1000000010000000... However, on the last word, if you cannot go past the end, you have to go one byte at a time. But, if you can go past the end, you can mask out the irrelevant bits and use the same mask as before. On Thu, Mar 8, 2018 at 1:35 PM, David Feuer wrote:

What do you gain from this?

On Mar 8, 2018 9:19 AM, "Andrew Martin" wrote:

...

Let's say I have a gc-managed byte array of length 19. GHC promises that byte arrays are machine-word-aligned on the front end. That is, on a 64-bit machine, this array starts on a memory address that divide 8 evenly. However, the back end will certainly be unaligned. So, these two calls will be fine:

- indexWordArray# myArr# 0# - indexWordArray# myArr# 1#

But this one is non-deterministic:

- indexWordArray# myArr# 2#

Some of the bytes in the word will have garbage in them. However, this could always be masked out with a bit mask (you have to know the platform endianness for this to work right). Is this safe? I doubt think this could ever cause a segfault but I wanted to check.

-- -Andrew Thaddeus Martin

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-- -Andrew Thaddeus Martin