On Wednesday, 22 May 2019 at 08:54:45 UTC, Russel Winder wrote:
On Tue, 2019-05-21 at 19:14 +0000, Era Scarecrow via
Digitalmars-d-learn wrote:
[…]
I worked on/with bitfields in the past, the limit sizes is
more
or less for natural int types that D supports.
Rust bitfield crate and it's macros are the same, the
underlying type for a bitfield must be a primitive integer
type. Fortunately, Rust has i128 and u128 which is enough for
my 112 bit EIT header.
Boris Barboris suggested using BitArray and I willinvestigate
but the size_t/byte problem would need to go away.
However this limitation is kinda arbitrary, as for
simplicity it
relies on shifting bits, going larger or any byte size is
possible depending on what needs to be stored, but ti's the
speed
that really takes a penalty when you aren't using native types
or
you have to do a lot of shifting to get the job done.
What's the layout of what you need? I'll see if i can't make
something that would work for you.
Would be better if you can use a object that breaks the parts
down and you can actually fully access those parts, then just
re-store it into the limited space you want for storage, which
then would be faster than bitfields (although not by much)
I found an interesting way forward in the source code of
dvbsnoop. It basically uses the byte sequence as a backing
store and then has a function to do the necessary accesses to
treat it as a bit array.
If D's Bit Array can work with bytes instead of size_t then it
is exactly what dvbsnoop does (in C) but adds writing as well
as reading.
The Rust solution using bitfield with a u128 backing it seems
to work, but it is all very clumsy even if it is efficacious.
If the type of operations you need on your 128 bit container is
simple enough (bitwise op) you can implement them, backed by two
ulong in a custom struct.
I did something similar for the tokens if my language[1]. There
are probably wrong stuff in there but for my usage (include and
bt) that works seamlessly.
[1]:
https://github.com/Basile-z/styx/blob/master/src/styx/data_structures.d#L40
