Function std.bitmanip.bitfields
Allows creating bitfields inside structs, classes and unions.
string bitfields(T...)();
A bitfield consists of one or more entries with a fixed number of
bits reserved for each of the entries. The types of the entries can
be bools, integral types or enumerated types, arbitrarily mixed.
The most efficient type to store in bitfields is bool, followed
by unsigned types, followed by signed types.
Each non-bool entry of the bitfield will be represented by the
number of bits specified by the user. The minimum and the maximum
numbers that represent this domain can be queried by using the name
of the variable followed by _min or _max.
Limitation
The number of bits in a bitfield is limited to 8, 16,
32 or 64. If padding is needed, an entry should be explicitly
allocated with an empty name.
Implementation details
Bitfields are internally stored in an
ubyte, ushort, uint or ulong depending on the number of bits
used. The bits are filled in the order given by the parameters,
starting with the lowest significant bit. The name of the (private)
variable used for saving the bitfield is created by a prefix _bf
and concatenating all of the variable names, each preceded by an
underscore.
Parameters
| Name | Description |
|---|---|
| T | A list of template parameters divided into chunks of 3
items. Each chunk consists (in this order) of a type, a
name and a number. Together they define an entry
of the bitfield: a variable of the given type and name,
which can hold as many bits as the number denotes. |
Returns
A string that can be used in a mixin to add the bitfield.
See Also
Example
Create a bitfield pack of eight bits, which fit in
one ubyte. The bitfields are allocated starting from the
least significant bit, i.e. x occupies the two least significant bits
of the bitfields storage.
struct A
{
int a;
mixin(bitfields!(
uint, "x", 2,
int, "y", 3,
uint, "z", 2,
bool, "flag", 1));
}
A obj;
objExample
The sum of all bit lengths in one bitfield instantiation
must be exactly 8, 16, 32, or 64. If padding is needed, just allocate
one bitfield with an empty name.
struct A
{
mixin(bitfields!(
bool, "flag1", 1,
bool, "flag2", 1,
uint, "", 6));
}
A a;
writeln(aExample
enums can be used too
enum ABC { A, B, C }
struct EnumTest
{
mixin(bitfields!(
ABC, "x", 2,
bool, "y", 1,
ubyte, "z", 5));
}
Authors
Walter Bright, Andrei Alexandrescu, Jonathan M Davis, Alex Rønne Petersen, Damian Ziemba, Amaury SECHET