Erlang比特语法
#Erlang比特语法
Value:Size/TypeSpecifierList
The Size or the TypeSpecifier, or both, can be omitted. Thus, the following variants are allowed:
- Value
- Value:Size
- Value/TypeSpecifierList
Default values are used when specifications are missing. The default values are described in Defaults.
The Value part is any expression, when used in binary construction. Used in binary matching, the Value part must be a literal or a variable. For more information about the Value part, see Constructing Binaries and Bitstrings and Matching Binaries.
The Size part of the segment multiplied by the unit in TypeSpecifierList (described later) gives the number of bits for the segment. In construction, Size is any expression that evaluates to an integer. In matching, Size must be a constant expression or a variable.
The TypeSpecifierList is a list of type specifiers separated by hyphens.
####Type
The type can be integer, float, or binary.
####Signedness
The signedness specification can be either signed or unsigned. Notice that signedness only matters for matching.
####Endianness
The endianness specification can be either big, little, or native. Native-endian means that the endian is resolved at load time, to be either big-endian or little-endian, depending on what is “native” for the CPU that the Erlang machine is run on.
####Unit
The unit size is given as unit:IntegerLiteral. The allowed range is 1-256. It is multiplied by the Size specifier to give the effective size of the segment. Since Erlang R12B, the unit size specifies the alignment for binary segments without size.
Example:
X:4/little-signed-integer-unit:8
This element has a total size of 4*8 = 32 bits, and it contains a signed integer in little-endian order.
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