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 calculus of variations functions.

use std::ffi::CStr;
use std::os::raw::c_char;

use crate::symbolic::calculus_of_variations;
use crate::symbolic::core::Expr;

/// # 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 fn c_str_to_str<'a>(s: *const c_char) -> Option<&'a str> {
    unsafe {
        if s.is_null() {
            None
        } else {
            CStr::from_ptr(s).to_str().ok()
        }
    }
}

/// Computes the Euler-Lagrange equation for a given Lagrangian.
///
/// # Safety
/// The caller must ensure `lagrangian` is a valid Expr pointer, and `func` and `var` are valid C strings.
///
/// # 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_euler_lagrange(
    lagrangian: *const Expr,
    func: *const c_char,
    var: *const c_char,
) -> *mut Expr {
    unsafe {
        if lagrangian.is_null() || func.is_null() || var.is_null() {
            return std::ptr::null_mut();
        }

        let lagrangian_ref = &*lagrangian;

        let func_str = match c_str_to_str(func) {
            | Some(s) => s,
            | None => return std::ptr::null_mut(),
        };

        let var_str = match c_str_to_str(var) {
            | Some(s) => s,
            | None => return std::ptr::null_mut(),
        };

        Box::into_raw(Box::new(calculus_of_variations::euler_lagrange(
            lagrangian_ref,
            func_str,
            var_str,
        )))
    }
}

/// Generates and attempts to solve the Euler-Lagrange equation.
///
/// # Safety
/// The caller must ensure `lagrangian` is a valid Expr pointer, and `func` and `var` are valid C strings.
///
/// # 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_solve_euler_lagrange(
    lagrangian: *const Expr,
    func: *const c_char,
    var: *const c_char,
) -> *mut Expr {
    unsafe {
        if lagrangian.is_null() || func.is_null() || var.is_null() {
            return std::ptr::null_mut();
        }

        let lagrangian_ref = &*lagrangian;

        let func_str = match c_str_to_str(func) {
            | Some(s) => s,
            | None => return std::ptr::null_mut(),
        };

        let var_str = match c_str_to_str(var) {
            | Some(s) => s,
            | None => return std::ptr::null_mut(),
        };

        Box::into_raw(Box::new(calculus_of_variations::solve_euler_lagrange(
            lagrangian_ref,
            func_str,
            var_str,
        )))
    }
}

/// Applies Hamilton's Principle to derive the equations of motion.
///
/// # Safety
/// The caller must ensure `lagrangian` is a valid Expr pointer, and `func` and `var` are valid C strings.
///
/// # 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_hamiltons_principle(
    lagrangian: *const Expr,
    func: *const c_char,
    var: *const c_char,
) -> *mut Expr {
    unsafe {
        if lagrangian.is_null() || func.is_null() || var.is_null() {
            return std::ptr::null_mut();
        }

        let lagrangian_ref = &*lagrangian;

        let func_str = match c_str_to_str(func) {
            | Some(s) => s,
            | None => return std::ptr::null_mut(),
        };

        let var_str = match c_str_to_str(var) {
            | Some(s) => s,
            | None => return std::ptr::null_mut(),
        };

        Box::into_raw(Box::new(calculus_of_variations::hamiltons_principle(
            lagrangian_ref,
            func_str,
            var_str,
        )))
    }
}