rssn 0.2.9

A comprehensive scientific computing library for Rust, aiming for feature parity with NumPy and SymPy.
Documentation 
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use std::collections::HashMap;
use std::ffi::CStr;
use std::os::raw::c_char;
use std::os::raw::c_int;

use crate::symbolic::core::Expr;
use crate::symbolic::optimize::CriticalPoint;
use crate::symbolic::optimize::find_constrained_extrema;
use crate::symbolic::optimize::find_extrema;
use crate::symbolic::optimize::hessian_matrix;

/// # 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 parse_c_str_array(
    arr: *const *const c_char,
    len: usize,
) -> Option<Vec<String>> {
    unsafe {
        if arr.is_null() {
            return None;
        }

        let mut vars = Vec::with_capacity(len);

        for i in 0..len {
            let ptr = *arr.add(i);

            if ptr.is_null() {
                return None;
            }

            let c_str = CStr::from_ptr(ptr);

            match c_str.to_str() {
                | Ok(s) => {
                    vars.push(s.to_string());
                },
                | Err(_) => {
                    return None;
                },
            }
        }

        Some(vars)
    }
}

/// Finds extrema of a function (Handle)
#[unsafe(no_mangle)]
pub extern "C" fn rssn_find_extrema_handle(
    expr_ptr: *const Expr,
    vars_ptr: *const *const c_char,
    vars_len: c_int,
) -> *mut Vec<CriticalPoint> {
    if expr_ptr.is_null() {
        return std::ptr::null_mut();
    }

    unsafe {
        let expr = &*expr_ptr;

        let vars_strings =
            match parse_c_str_array(vars_ptr, i64::from(vars_len).try_into().unwrap_or(0)) {
                | Some(v) => v,
                | None => return std::ptr::null_mut(),
            };

        let vars_refs: Vec<&str> = vars_strings
            .iter()
            .map(std::string::String::as_str)
            .collect();

        match find_extrema(expr, &vars_refs) {
            | Ok(points) => Box::into_raw(Box::new(points)),
            | Err(_) => std::ptr::null_mut(),
        }
    }
}

/// Computes Hessian matrix (Handle)
#[unsafe(no_mangle)]
pub extern "C" fn rssn_hessian_matrix_handle(
    expr_ptr: *const Expr,
    vars_ptr: *const *const c_char,
    vars_len: c_int,
) -> *mut Expr {
    if expr_ptr.is_null() {
        return std::ptr::null_mut();
    }

    unsafe {
        let expr = &*expr_ptr;

        let vars_strings =
            match parse_c_str_array(vars_ptr, i64::from(vars_len).try_into().unwrap_or(0)) {
                | Some(v) => v,
                | None => return std::ptr::null_mut(),
            };

        let vars_refs: Vec<&str> = vars_strings
            .iter()
            .map(std::string::String::as_str)
            .collect();

        let hessian = hessian_matrix(expr, &vars_refs);

        Box::into_raw(Box::new(hessian))
    }
}

/// Finds constrained extrema (Handle)
#[unsafe(no_mangle)]
pub extern "C" fn rssn_find_constrained_extrema_handle(
    expr_ptr: *const Expr,
    constraints_ptr: *const Vec<Expr>,
    vars_ptr: *const *const c_char,
    vars_len: c_int,
) -> *mut Vec<HashMap<Expr, Expr>> {
    if expr_ptr.is_null() || constraints_ptr.is_null() {
        return std::ptr::null_mut();
    }

    unsafe {
        let expr = &*expr_ptr;

        let constraints = &*constraints_ptr;

        let vars_strings =
            match parse_c_str_array(vars_ptr, i64::from(vars_len).try_into().unwrap_or(0)) {
                | Some(v) => v,
                | None => return std::ptr::null_mut(),
            };

        let vars_refs: Vec<&str> = vars_strings
            .iter()
            .map(std::string::String::as_str)
            .collect();

        match find_constrained_extrema(expr, constraints, &vars_refs) {
            | Ok(solutions) => Box::into_raw(Box::new(solutions)),
            | Err(_) => std::ptr::null_mut(),
        }
    }
}

/// Frees a Vec`<CriticalPoint>` handle
#[unsafe(no_mangle)]
pub extern "C" fn rssn_free_critical_point_vec_handle(ptr: *mut Vec<CriticalPoint>) {
    if !ptr.is_null() {
        unsafe {
            let _ = Box::from_raw(ptr);
        }
    }
}

/// Frees a Vec<`HashMap`<Expr, Expr>> handle
#[unsafe(no_mangle)]
#[allow(clippy::implicit_hasher)]
pub extern "C" fn rssn_free_solution_vec_handle(ptr: *mut Vec<HashMap<Expr, Expr>>) {
    if !ptr.is_null() {
        unsafe {
            let _ = Box::from_raw(ptr);
        }
    }
}