lfe_bits.erl - Bitstring Specification

Purpose: Parse and validate bitstring segment specifications.

Location: src/lfe_bits.erl Size: 137 LOC, 5.0KB

Module Classification: Library support, binary handling

Public API

get_bitspecs(Specs) -> {Type, Size, Unit, Sign, Endian}

Parse bitstring specifications. Located at lfe_bits.erl:37-41.

Specification Format

Segment Specs (from binary syntax):

#B(value)                    ; Default: 8-bit unsigned int
#B((value integer))          ; Explicit type
#B((value (size 16)))        ; 16-bit
#B((value integer (size 16) big unsigned))  ; Full spec

Types:

• integer - Integer value
• float - Floating-point
• binary - Binary/bitstring
• bytes - Alias for binary
• bitstring - Bitstring
• utf8, utf16, utf32 - UTF encoding

Modifiers:

• (size N) - Bit size
• (unit N) - Unit size (for binary/bitstring)
• signed, unsigned - Sign
• big, little, native - Endianness

Parsing

Spec Parser (parse_spec/1 at lines 78-134):

parse_spec([integer|Rest]) ->
    parse_spec(Rest, {integer, default, 1, unsigned, big});
parse_spec([float|Rest]) ->
    parse_spec(Rest, {float, 64, 1, unsigned, big});
parse_spec([(size, N)|Rest], {T, _, U, S, E}) ->
    parse_spec(Rest, {T, N, U, S, E});
parse_spec([signed|Rest], {T, Sz, U, _, E}) ->
    parse_spec(Rest, {T, Sz, U, signed, E});
...

Defaults:

Dependencies

• lists (Erlang stdlib)

Used By

• lfe_eval_bits - Runtime binary operations
• lfe_translate - Compile-time binary translation

Special Considerations

Validation: Ensures specs are valid (e.g., float must be 32 or 64 bits).

Error Reporting: Returns descriptive errors for invalid specs.