oxifft-codegen-impl

Version: 0.3.1

Internal codelet generation logic for OxiFFT.

This crate provides the core symbolic computation and codelet-generation engine used by oxifft-codegen (the procedural macro crate) and by oxifft-bench (for benchmarking codelet generation throughput). It is not a proc-macro crate — it is a regular library that oxifft-codegen depends on to work around the proc-macro crate limitation that prevents exposing non-macro public APIs.

Overview

Symbolic DFT engine — represents FFT butterfly operations symbolically as expression trees, enabling algebraic simplification and strength reduction before code generation.
Codelet generators — emit Rust token streams for radix-2/4/8 and mixed-radix NOTW (no-twiddle) kernels, RDFT codelets, and SIMD-specialized variants for x86-64 (AVX2/SSE2) and AArch64 (NEON/SVE).
Optimization passes — dead-code elimination, constant folding, common sub-expression elimination, and strength reduction (mul-by-1 → identity, mul-by-0 → zero).
Universal dispatcher — gen_any module classifies any FFT size and routes it to the optimal codelet path (hardcoded, MixedRadix, Rader, or Bluestein).

Usage

This crate is an implementation detail of oxifft-codegen. Users of OxiFFT should depend on oxifft directly; oxifft-codegen-impl is re-exported through the proc-macro interface automatically.

# In your Cargo.toml — depend on oxifft, not on this crate directly
[dependencies]
oxifft = "0.3"

If you are building tooling that needs access to the codelet generation internals (e.g. a custom benchmark harness or a code-generation analysis tool), you may depend on this crate directly:

[dev-dependencies]
oxifft-codegen-impl = "0.3"

Modules

Module	Description
`emit`	Core token-stream emitters for NOTW, twiddle, RDFT, and SIMD codelets
`gen_any`	Universal dispatcher — classifies `N` and selects the optimal path
`gen_mixed_radix`	MixedRadix runtime-wrapper generator for smooth-7 composite sizes
`optimize`	DCE, constant folding, CSE, and strength-reduction passes
`symbolic`	Expression DAG for symbolic FFT butterfly operations

Public API

`classify(n: usize) -> SizeClass`

Classifies an FFT size into the appropriate generation strategy:

use oxifft_codegen_impl::classify;

match classify(13) {
    SizeClass::Hardcoded  => { /* direct codelet */ }
    SizeClass::MixedRadix => { /* smooth-7 composite */ }
    SizeClass::Rader      => { /* prime ≤ 1021 */ }
    SizeClass::Bluestein  => { /* general fallback */ }
}

`SizeClass` enum

SizeClass::Hardcoded   — N ∈ {2,3,4,5,7,8,11,13,16,32,64}
SizeClass::MixedRadix  — N smooth-7 composite not in the hardcoded set
SizeClass::Rader       — N prime, 1021 ≥ N > 64 and not hardcoded
SizeClass::Bluestein   — all other N

`CodeletBuilder`

Programmatic API for constructing a single codelet:

use oxifft_codegen_impl::{CodeletBuilder, Precision, Direction};

let tokens = CodeletBuilder::new(16)
    .precision(Precision::F64)
    .direction(Direction::Forward)
    .build();

Test Count

213 tests in oxifft-codegen-impl + 56 tests in oxifft-codegen = 269 total.

License

Apache-2.0. See LICENSE.

oxifft-codegen-impl 0.3.1