Comments (6)
Robbepop
commented on August 16, 2024
If the overall struct is 4096 bytes I think it makes sense to better split it up into different components. Not the entire thing must be wrapped in a #[modular_bitfield] proc. macro. I won't dig into the linked PDF and search for all the information required but generally you only need bitfields in cases where bits are stored in chunks that do not align with 8 bits. Storing an array probably won't need a modular bitfield - and if so I'd recommend you to rethink the data structure. It would only need a bitfield if the array is not aligned to 8 bits.
If you want you can paste the structure here with information as in:
| Bits | Field | Type |
|---|---|---|
| 0..5 | some_flag |
i8 |
| 5..6 | is_alive |
bool |
| etc. | etc. | etc. |
And we sure will find some proper solution.
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ethindp
commented on August 16, 2024
I'm not sure why you can't look up the figures I indicated. The primary figure I'm speaking about is figure 251, in section 5.15.2.2. The one with reserved bits is also within that figure, bytes 95:92. That has the following layout:
| Bits | Description | Type |
|---|---|---|
| 31:15 | Reserved | u16 |
| 14 | Endurance Group Event Aggregate Log Page Change Notices event supported | bool |
| 13 | LBA Status Information Notices event supported | bool |
| 12 | Predictable Latency Event Aggregate Log Change Notices event supported | bool |
| 11 | Sending Asymmetric Namespace Access Change Notices supported | bool |
| 10 | Reserved | bool |
| 9 | Firmware activation notices event supported | bool |
| 8 | Namespace Attribute Notices event and Changed Namespace List log page supported | bool |
| 7:0 | Reserved | [bool; 8] |
I could probably just make a recursive bitfield out of this, come to think of it.
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Robbepop
commented on August 16, 2024
Hi, sorry I completely forgot about this thread.
From what it looks you can easily represent all the sub parts of the entire structure as you have just laid out 32 bits of one.
The reserved bits in 7:0 should probably be represented as a single u8 instead of a [bool; 8] field.
However, your suggestion to maybe add [bool; 8] is legit and might even be possible, however only with some conversion overhead I suppose since bool is not really a 1 bit width type.
So to answer your original question: Yes this crate should be sufficient for your needs from what it looks like on the surface.
Of course trust yourself always the most. Use u8 or other small types such as BN instead of arrays for reserved holes.
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ethindp
commented on August 16, 2024
Thank you. Is the crate able to handle array types? If not that would
be an appreciated addition. I'm thinking of using this on really large
structs that have large blocks of reserved or undefined data, and
right now I have to use crazy slice::align_to() magic to actually do
it, as well as representing the struct using #[repr(C, packed)]. I'd
love to add this myself but I honestly have no idea how; I've never
worked with rust attribute macros before so I have no idea how they
work.
…On 2/28/21, Hero Bird ***@***.***> wrote:
Hi, sorry I completely forgot about this thread.
From what it looks you can easily represent all the sub parts of the entire
structure as you have just laid out 32 bits of one.
The reserved bits in `7:0` should probably be represented as a single `u8`
instead of a `[bool; 8]` field.
However, your suggestion to maybe add `[bool; 8]` is legit and might even be
possible, however only with some conversion overhead I suppose since `bool`
is not really a 1 bit width type.
So to answer your original question: Yes this crate should be sufficient for
your needs from what it looks like on the surface.
Of course trust yourself always the most. Use `u8` or other small types
instead of arrays for reserved holes.
--
You are receiving this because you authored the thread.
Reply to this email directly or view it on GitHub:
#61 (comment)
--
Signed,
Ethin D. Probst
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Robbepop
commented on August 16, 2024
I think it is a better decision to use this crate's modular bitfields only for well defined subsets of your structs with giant reserved voids. So just have your entire struct and within the struct have reserved fields that simply use some arrays or whatever you used before and for the well defined subsets use this crate's modular bitfield structs as fields. This should work very efficiently as long as your reserved data is 8 bit aligned. (I hope it is.)
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ethindp
commented on August 16, 2024
I could do that, but how would I then load it into memory? I'm only
given a stream of bytes, and there's *a lot* of bytes to load. I don't
mind doing it manually, it'll just be a pain and I'd (preferably) like
to make it as easy to read and as simple as possible. Like I don't
want to be calling ::from_*_bytes() all over the place and that kind
of thing.
…On 2/28/21, Hero Bird ***@***.***> wrote:
I think it is a better decision to use this crate's modular bitfields only
for well defined subsets of your structs with giant reserved voids. So just
have your entire struct and within the struct have reserved fields that
simply use some arrays or whatever you used before and for the well defined
subsets use this crate's modular bitfield structs as fields.
--
You are receiving this because you authored the thread.
Reply to this email directly or view it on GitHub:
#61 (comment)
--
Signed,
Ethin D. Probst
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Related Issues (20)
- Support for `to_u32()` conversion to `u32` and similar
- #[bitfield] on empty struct causes compilation error
- Feature Request: Ability to specify default value for field
- Is this crate maintained? HOT 1
- Implement serde derives replacement HOT 2
- Feature request: Array support HOT 3
- Into<uN> and TryFrom<uN> for uN bitfields HOT 2
- `with_*` methods should have `#[must_use]` annotation HOT 2
- Help: CheckFillsUnalignedBits unsatisfied HOT 2
- Support rust union structs HOT 1
- Feature request: Allow naming fields "Bytes" HOT 1
- Question: Array of bitfields HOT 1
- #[repr(...)] for unfilled bitfields?
- Generic structs not supported HOT 7
- [Question] Polymorphic bitfileds HOT 1
- Support for byte arrays
- `#[non_exhaustive]` enum support HOT 9
- const fn support for getters (and setters if possible) HOT 1
- How to implement signed 10 bit number? HOT 8
- [Feature Request] Better Note for (Size % 8)
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