Update to non-avx builds

poulpy-cpu-avx/README.md

@@ -1,8 +1,51 @@
-# 🐙 Poulpy-CPU-REF
+# 🐙 Poulpy-CPU-AVX
 
-**Poulpy-Backend-CPU-AVX** is a Rust crate that provides an AVX accelerated CPU implementation of **`poulpy-hal`**. This crate is used to instantiate projects implemented with **`poulpy-hal`**, **`poulpy-core`** and/or **`poulpy-schemes`**.
+**Poulpy-CPU-AVX** is a Rust crate that provides an **AVX2 + FMA accelerated CPU backend for Poulpy**.
 
-## Example
+This backend implements the Poulpy HAL extension traits and can be used by:
+
+- [`poulpy-hal`](https://github.com/phantomzone-org/poulpy/tree/main/poulpy-hal)
+- [`poulpy-core`](https://github.com/phantomzone-org/poulpy/tree/main/poulpy-core)
+- [`poulpy-schemes`](https://github.com/phantomzone-org/poulpy/tree/main/poulpy-schemes)
+
+## 🚩 Safety and Requirements
+
+To avoid illegal hardware instructions (SIGILL) on unsupported CPUs, this backend is **opt-in** and **only builds when explicitly requested**.
+
+| Requirement | Status |
+|------------|--------|
+| Cargo feature flag | `--features enable-avx` **must be enabled** |
+| CPU architecture | `x86_64` |
+| CPU target features | `AVX2` + `FMA` |
+
+If `enable-avx` is enabled but the target does not provide these capabilities, the build **fails immediately with a clear error message**, rather than generating invalid binaries.
+
+When `enable-avx` is **not** enabled, this crate is simply skipped and Poulpy automatically falls back to the portable `poulpy-cpu-ref` backend. This ensure that Poulpy's workspace remains portable (e.g. for macOS ARM).
+
+## ⚙️ Building with the AVX backend enabled
+
+Because the compiler must generate AVX2 + FMA instructions, both the Cargo feature and CPU target flags must be specified:
+
+```bash
+RUSTFLAGS="-C target-feature=+avx2,+fma" \
+cargo build --features enable-avx
+````
+
+### Running an example
+
+```bash
+RUSTFLAGS="-C target-feature=+avx2,+fma" \
+cargo run --example <name> --features enable-avx
+```
+
+### Running benchmarks
+
+```bash
+RUSTFLAGS="-C target-feature=+avx2,+fma" \
+cargo bench --features enable-avx
+```
+
+## Basic Usage
 
 ```rust
 use poulpy_backend_cpu_avx::FFT64Avx;
@@ -12,7 +55,24 @@ let log_n: usize = 10;
 let module = Module<FFT64Avx> = Module<FFT64Avx>::new(1<<log_n);
 ```
 
-## Contributors
+Once compiled with `enable-avx`, the backend is usable transparently anywhere Poulpy expects a backend type (`poulpy-hal`, `poulpy-core`, `poulpy-schemes`).
 
-To add your own backend, implement the open extension traits from **`poulpy-hal/oep`** for a struct that implements the `Backend` trait.  
-This will automatically make your backend compatible with the API of **`poulpy-hal`**, **`poulpy-core`** and **`poulpy-schemes`**.
+## 🤝 Contributors
+
+To implement your own Poulpy backend (SIMD or accelerator):
+
+1. Define a backend struct
+2. Implement the open extension traits from `poulpy-hal/oep`
+3. Implement the `Backend` trait
+
+Your backend will automatically integrate with:
+
+* `poulpy-hal`
+* `poulpy-core`
+* `poulpy-schemes`
+
+No modifications to those crates are required — the HAL provides the extension points.
+
+---
+
+For questions or guidance, feel free to open an issue or discussion in the repository.