rssn 0.2.9

A comprehensive scientific computing library for Rust, aiming for feature parity with NumPy and SymPy.
Documentation 
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//! Handle-based FFI API for physics MTM (Multigrid) functions.

use std::ptr;

use crate::physics::physics_mtm;

/// Solves 1D Poisson using Multigrid and returns a flat array of doubles.
///
/// The `out_size` will be set to `n + 2` (including boundaries).
/// The caller is responsible for freeing the memory using `rssn_free_f64_mtm_array`.
///
/// # 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_mtm_solve_poisson_1d(
    n_interior: usize,
    f: *const f64,
    num_cycles: usize,
    out_size: *mut usize,
) -> *mut f64 {
    unsafe {
        if f.is_null() {
            return ptr::null_mut();
        }

        let f_slice = std::slice::from_raw_parts(f, n_interior);

        match physics_mtm::solve_poisson_1d_multigrid(n_interior, f_slice, num_cycles) {
            | Ok(res) => {
                *out_size = res.len();

                let mut res_boxed = res.into_boxed_slice();

                let ptr = res_boxed.as_mut_ptr();

                std::mem::forget(res_boxed);

                ptr
            },
            | Err(_) => {
                *out_size = 0;

                ptr::null_mut()
            },
        }
    }
}

/// Solves 2D Poisson using Multigrid and returns a flat array of doubles.
/// The `out_size` will be set to `n * n`.
///
/// # 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_mtm_solve_poisson_2d(
    n: usize,
    f: *const f64,
    num_cycles: usize,
    out_size: *mut usize,
) -> *mut f64 {
    unsafe {
        if f.is_null() {
            return ptr::null_mut();
        }

        let f_slice = std::slice::from_raw_parts(f, n * n);

        match physics_mtm::solve_poisson_2d_multigrid(n, f_slice, num_cycles) {
            | Ok(res) => {
                *out_size = res.len();

                let mut res_boxed = res.into_boxed_slice();

                let ptr = res_boxed.as_mut_ptr();

                std::mem::forget(res_boxed);

                ptr
            },
            | Err(_) => {
                *out_size = 0;

                ptr::null_mut()
            },
        }
    }
}

/// Frees a float64 array allocated by the MTM FFI.
///
/// # 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_free_f64_mtm_array(
    ptr: *mut f64,
    size: usize,
) {
    unsafe {
        if !ptr.is_null() {
            let _ = Box::from_raw(std::ptr::slice_from_raw_parts_mut(ptr, size));
        }
    }
}