# `ToonEx.Decode.Codegen`
[🔗](https://github.com/ohhi-vn/toon_ex/blob/v1.1.0/lib/toon_ex/decode/codegen.ex#L1)

Compile-time code generation utilities for the TOON decoder.

Inspired by `Jason.Codegen`, this module provides macros for generating
efficient byte-level dispatch tables at compile time. This replaces runtime
regex checks and `String.contains?` calls with O(1) binary pattern matching.

## How it works

The `bytecase/2` macro generates a `case` expression on a binary where each
clause matches a specific leading byte. This is more efficient than calling
`String.starts_with?/2` or regex matching because:

1. The BEAM compiler optimizes binary pattern matching into a jump table
2. No intermediate string allocations
3. The dispatch is O(1) regardless of the number of clauses

## Example

    bytecase data do
      _ in ~c'0123456789', rest ->
        parse_number(rest)
      _ in ~c'"', rest ->
        parse_string(rest)
      _, rest ->
        error(rest)
    end

Generates:

    case data do
      <<48, rest::bits>> -> parse_number(rest)
      <<49, rest::bits>> -> parse_number(rest)
      ...
      <<34, rest::bits>> -> parse_string(rest)
      <<byte, rest::bits>> -> error(rest)
    end

# `bytecase`
*macro* 

Generates a `case` expression that dispatches on the first byte of a binary.

## Clause syntax

    bytecase var do
      _ in ~c'abc', rest ->
        # matches bytes 97, 98, 99
        handle_abc(rest)

      _ in 0..31, rest ->
        # matches bytes 0-31
        handle_control(rest)

      _, rest ->
        # default clause
        handle_other(rest)
    end

The `_` in patterns is the byte variable (unused but required for syntax).
The second element `rest` captures the remaining binary.

# `bytecase`
*macro* 

Like `bytecase/2` but with an explicit max byte value for the jump table.
Useful when you want to cover all bytes up to a certain value.

# `jump_table`

Builds a compile-time jump table from byte ranges.

Returns a list of `{byte_value, action}` tuples suitable for generating
case clauses.

# `jump_table`

---

*Consult [api-reference.md](api-reference.md) for complete listing*