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 classical mechanics functions.

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

use crate::symbolic::classical_mechanics;
use crate::symbolic::core::Expr;
use crate::symbolic::vector::Vector;
use crate::symbolic::vector_calculus::ParametricCurve;

/// # 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()
        }
    }
}

/// Calculates kinetic energy: 1/2 * m * v^2.
///
/// # 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_kinetic_energy(
    mass: *const Expr,
    velocity: *const Expr,
) -> *mut Expr {
    unsafe {
        if mass.is_null() || velocity.is_null() {
            return std::ptr::null_mut();
        }

        Box::into_raw(Box::new(classical_mechanics::kinetic_energy(
            &*mass, &*velocity,
        )))
    }
}

/// Calculates Lagrangian: T - V.
///
/// # 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_lagrangian(
    t: *const Expr,
    v: *const Expr,
) -> *mut Expr {
    unsafe {
        if t.is_null() || v.is_null() {
            return std::ptr::null_mut();
        }

        Box::into_raw(Box::new(classical_mechanics::lagrangian(&*t, &*v)))
    }
}

/// Calculates Hamiltonian: T + V.
///
/// # 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_hamiltonian(
    t: *const Expr,
    v: *const Expr,
) -> *mut Expr {
    unsafe {
        if t.is_null() || v.is_null() {
            return std::ptr::null_mut();
        }

        Box::into_raw(Box::new(classical_mechanics::hamiltonian(&*t, &*v)))
    }
}

/// Computes Euler-Lagrange equation.
///
/// # 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_equation(
    lagrangian: *const Expr,
    q: *const c_char,
    q_dot: *const c_char,
    t_var: *const c_char,
) -> *mut Expr {
    unsafe {
        if lagrangian.is_null() || q.is_null() || q_dot.is_null() || t_var.is_null() {
            return std::ptr::null_mut();
        }

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

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

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

        Box::into_raw(Box::new(classical_mechanics::euler_lagrange_equation(
            &*lagrangian,
            q_str,
            q_dot_str,
            t_str,
        )))
    }
}

/// Calculates torque: r x F.
///
/// # 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_torque(
    r: *const Vector,
    force: *const Vector,
) -> *mut Vector {
    unsafe {
        if r.is_null() || force.is_null() {
            return std::ptr::null_mut();
        }

        Box::into_raw(Box::new(classical_mechanics::torque(&*r, &*force)))
    }
}

/// Calculates power: F . v.
///
/// # 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_power(
    force: *const Vector,
    velocity: *const Vector,
) -> *mut Expr {
    unsafe {
        if force.is_null() || velocity.is_null() {
            return std::ptr::null_mut();
        }

        Box::into_raw(Box::new(classical_mechanics::power(&*force, &*velocity)))
    }
}

/// Calculates work done by a variable force field along a path.
///
/// # 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_work_line_integral(
    force_field: *const Vector,
    path: *const ParametricCurve,
) -> *mut Expr {
    unsafe {
        if force_field.is_null() || path.is_null() {
            return std::ptr::null_mut();
        }

        Box::into_raw(Box::new(classical_mechanics::work_line_integral(
            &*force_field,
            &*path,
        )))
    }
}