rssn 0.2.9

A comprehensive scientific computing library for Rust, aiming for feature parity with NumPy and SymPy.
Documentation 
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//! Bincode-based FFI API for physics EM functions.

use serde::Deserialize;

use crate::ffi_apis::common::BincodeBuffer;
use crate::ffi_apis::common::from_bincode_buffer;
use crate::ffi_apis::common::to_bincode_buffer;
use crate::ffi_apis::ffi_api::FfiResult;
use crate::physics::physics_em;
use crate::physics::physics_rkm::DampedOscillatorSystem;
use crate::physics::physics_rkm::LorenzSystem;

#[derive(Deserialize)]
struct EulerInput {
    system_type: String,
    params_bincode: Vec<u8>,
    y0: Vec<f64>,
    t_span: (f64, f64),
    dt: f64,
    method: String,
}

/// Solves ODE systems using Euler methods (forward, midpoint, or Heun) via bincode serialization.
///
/// Supports various dynamical systems including Lorenz attractor and damped oscillators,
/// using explicit Euler integration methods.
///
/// # Arguments
///
/// * `buffer` - A bincode-encoded buffer containing `EulerInput` with:
///   - `system_type`: System identifier ("lorenz", "oscillator")
///   - `params_bincode`: System parameters encoded with bincode
///   - `y0`: Initial state vector
///   - `t_span`: Time interval (`t_start`, `t_end`)
///   - `dt`: Time step size
///   - `method`: Integration method ("forward", "midpoint", "heun")
///
/// # Returns
///
/// A bincode-encoded buffer containing `FfiResult<Vec<(f64, Vec<f64>)>, String>` with either:
/// - `ok`: Trajectory as (time, state) pairs
/// - `err`: Error message if computation failed
///
/// # Safety
///
/// This function is unsafe because it receives a raw bincode buffer that must be
/// valid and properly encoded.
///
/// # Safety
///
/// This function is unsafe because it dereferences raw pointers as part of the FFI boundary.
/// The caller must ensure:
/// 1. All pointer arguments are valid and point to initialized memory.
/// 2. The memory layout of passed structures matches the expected C-ABI layout.
/// 3. Any pointers returned by this function are managed according to the API's ownership rules.
#[unsafe(no_mangle)]
pub unsafe extern "C" fn rssn_physics_em_solve_bincode(buffer: BincodeBuffer) -> BincodeBuffer {
    let input: EulerInput = match from_bincode_buffer(&buffer) {
        | Some(i) => i,
        | None => {
            return to_bincode_buffer(&FfiResult::<Vec<(f64, Vec<f64>)>, String>::err(
                "Invalid Bincode".to_string(),
            ));
        },
    };

    let res = match input.system_type.as_str() {
        | "lorenz" => {
            let (sys, _): (LorenzSystem, usize) = match bincode_next::serde::decode_from_slice(
                &input.params_bincode,
                bincode_next::config::standard(),
            ) {
                | Ok(s) => s,
                | Err(e) => {
                    return to_bincode_buffer(&FfiResult::<Vec<(f64, Vec<f64>)>, String>::err(
                        e.to_string(),
                    ));
                },
            };

            solve_with_method(&sys, &input.y0, input.t_span, input.dt, &input.method)
        },
        | "oscillator" => {
            let (sys, _): (DampedOscillatorSystem, usize) =
                match bincode_next::serde::decode_from_slice(
                    &input.params_bincode,
                    bincode_next::config::standard(),
                ) {
                    | Ok(s) => s,
                    | Err(e) => {
                        return to_bincode_buffer(&FfiResult::<Vec<(f64, Vec<f64>)>, String>::err(
                            e.to_string(),
                        ));
                    },
                };

            solve_with_method(&sys, &input.y0, input.t_span, input.dt, &input.method)
        },
        | _ => {
            return to_bincode_buffer(&FfiResult::<Vec<(f64, Vec<f64>)>, String>::err(
                "Unknown system \
                     type"
                    .to_string(),
            ));
        },
    };

    to_bincode_buffer(&FfiResult::<Vec<(f64, Vec<f64>)>, String>::ok(res))
}

pub(crate) fn solve_with_method<S: crate::physics::physics_rkm::OdeSystem>(
    sys: &S,
    y0: &[f64],
    t_span: (f64, f64),
    dt: f64,
    method: &str,
) -> Vec<(f64, Vec<f64>)> {
    match method {
        | "midpoint" => physics_em::solve_midpoint_euler(sys, y0, t_span, dt),
        | "heun" => physics_em::solve_heun_euler(sys, y0, t_span, dt),
        | _ => physics_em::solve_forward_euler(sys, y0, t_span, dt),
    }
}