oxifft-codegen

Procedural macro crate for OxiFFT codelet generation.

Overview

This crate replaces FFTW's OCaml-based genfft code generator with Rust procedural macros. It generates highly optimized FFT kernels (codelets) at compile time.

Features

• Compile-time code generation: Zero runtime overhead
• Optimized kernels: Common subexpression elimination, strength reduction
• Multiple sizes: Support for sizes 2, 4, 8, 16, 32, 64
• Twiddle variants: Both non-twiddle (base case) and twiddle codelets
• SIMD-aware: Can generate SIMD-specific code patterns

Codelet Types

Non-Twiddle Codelets (notw)

Base case FFT kernels that don't require twiddle factors. Used at the leaves of the FFT recursion.

use oxifft_codegen::gen_notw_codelet;

// Generates codelet_notw_8 function
gen_notw_codelet!(8);

Twiddle Codelets

FFT kernels that apply twiddle factors as part of the Cooley-Tukey recursion.

use oxifft_codegen::gen_twiddle_codelet;

// Generates codelet_twiddle_4 function
gen_twiddle_codelet!(4);

SIMD Codelets

Architecture-specific SIMD-optimized kernels.

use oxifft_codegen::gen_simd_codelet;

// Generates SIMD-optimized size-8 codelet
gen_simd_codelet!(8);

Code Generation Strategy

The codelet generator follows FFTW's approach:

1. Symbolic representation: Build a DAG of FFT operations
2. Optimization passes:
   • Common subexpression elimination (CSE)
   • Strength reduction (replace multiplications with additions where possible)
   • Dead code elimination
3. Code emission: Generate Rust code with optimal instruction ordering

Supported Sizes

Implementation Notes

• Uses proc-macro2, quote, and syn for macro implementation
• Generated code is generic over the Float trait (f32/f64)
• Follows FFTW's codelet naming conventions for compatibility

License

Same as the parent OxiFFT project.