Update to non-avx builds

poulpy-cpu-ref/README.md

@@ -1,18 +1,93 @@
-# 🐙 Poulpy-CPU-AVX
+# 🐙 Poulpy-CPU-REF
 
-**Poulpy-Backend-CPU-AVX** is a Rust crate that provides the reference CPU implementation of **`poulpy-hal`**. This crate is used to instantiate projects implemented with **`poulpy-hal`**, **`poulpy-core`** and/or **`poulpy-schemes`**.
+**Poulpy-CPU-REF** is the **reference (portable) CPU backend for Poulpy**.
 
-## Example
+It implements the Poulpy HAL extension traits without requiring SIMD or specialized CPU instructions, making it suitable for:
+
+- all CPU architectures (`x86_64`, `aarch64`, `arm`, `riscv64`, …)
+- development machines and CI runners
+- environments without AVX or other advanced SIMD support
+
+This backend integrates transparently with:
+
+- `poulpy-hal`
+- `poulpy-core`
+- `poulpy-schemes`
+
+---
+
+## When is this backend used?
+
+`poulpy-cpu-ref` is always available and requires **no compilation flags and no CPU features**.
+
+It is automatically selected when:
+
+- the project does not request an optimized backend, or
+- the target CPU does not support the requested SIMD backend (e.g., AVX), or
+- portability and reproducibility are more important than raw performance.
+
+No additional configuration is required to use it.
+
+---
+
+## 🧪 Basic Usage
 
 ```rust
-use poulpy_backend_cpu_ref::FFT64Ref;
+use poulpy_cpu_ref::FFT64Ref;
 use poulpy_hal::{api::ModuleNew, layouts::Module};
 
 let log_n: usize = 10;
-let module = Module<FFT64Ref> = Module<FFT64Ref>::new(1<<log_n);
+let module: Module<FFT64Ref> = Module::<FFT64Ref>::new(1 << log_n);
 ```
 
-## Contributors
+This works on **all supported platforms and architectures**.
 
-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`**.
+---
+
+## Performance Notes
+
+`poulpy-cpu-ref` prioritizes:
+
+* portability
+* correctness
+* ease of debugging
+
+For maximum performance on x86_64 CPUs with AVX2 + FMA support, consider enabling the optional optimized backend:
+
+```
+poulpy-cpu-avx (feature: enable-avx)
+```
+
+Benchmarks and applications can freely switch between backends without changing source code — backend selection can be handled with feature flags, for example
+
+```rust
+#[cfg(all(feature = "enable-avx", target_arch = "x86_64", target_feature = "avx2", target_feature = "fma"))]
+use poulpy_cpu_avx::FFT64Avx as BackendImpl;
+
+#[cfg(not(all(feature = "enable-avx", target_arch = "x86_64", target_feature = "avx2", target_feature = "fma")))]
+use poulpy_cpu_ref::FFT64Ref as BackendImpl;
+```
+
+---
+
+## 🤝 Contributors
+
+To implement your own 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 necessary — the HAL provides the extension points.
+
+---
+
+For questions or guidance, feel free to open an issue or discussion in the repository.
+
+```