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

use crate::ffi_apis::common::from_json_string;
use crate::ffi_apis::common::to_json_string;
use crate::symbolic::core::Expr;
use crate::symbolic::polynomial::expr_to_sparse_poly;
use crate::symbolic::polynomial::sparse_poly_to_expr;
use crate::symbolic::real_roots::count_real_roots_in_interval;
use crate::symbolic::real_roots::isolate_real_roots;
use crate::symbolic::real_roots::sturm_sequence;

/// Generates the Sturm sequence for a given polynomial (JSON)
#[unsafe(no_mangle)]
pub extern "C" fn rssn_json_sturm_sequence(
    expr_json: *const c_char,
    var_ptr: *const c_char,
) -> *mut c_char {
    let expr: Option<Expr> = from_json_string(expr_json);

    if let Some(e) = expr {
        unsafe {
            if var_ptr.is_null() {
                return std::ptr::null_mut();
            }

            let var_cstr = CStr::from_ptr(var_ptr);

            let var_str = match var_cstr.to_str() {
                | Ok(s) => s,
                | Err(_) => return std::ptr::null_mut(),
            };

            let poly = expr_to_sparse_poly(&e, &[var_str]);

            let seq = sturm_sequence(&poly, var_str);

            let expr_seq: Vec<Expr> = seq.into_iter().map(|p| sparse_poly_to_expr(&p)).collect();

            to_json_string(&expr_seq)
        }
    } else {
        std::ptr::null_mut()
    }
}

/// Counts the number of distinct real roots in an interval (JSON)
#[unsafe(no_mangle)]
pub extern "C" fn rssn_json_count_real_roots_in_interval(
    expr_json: *const c_char,
    var_ptr: *const c_char,
    a: f64,
    b: f64,
) -> i64 {
    let expr: Option<Expr> = from_json_string(expr_json);

    if let Some(e) = expr {
        unsafe {
            if var_ptr.is_null() {
                return -1;
            }

            let var_cstr = CStr::from_ptr(var_ptr);

            let var_str = match var_cstr.to_str() {
                | Ok(s) => s,
                | Err(_) => return -1,
            };

            let poly = expr_to_sparse_poly(&e, &[var_str]);

            match count_real_roots_in_interval(&poly, var_str, a, b) {
                | Ok(count) => count as i64,
                | Err(_) => -1,
            }
        }
    } else {
        -1
    }
}

/// Isolates real roots in an interval (JSON)
#[unsafe(no_mangle)]
pub extern "C" fn rssn_json_isolate_real_roots(
    expr_json: *const c_char,
    var_ptr: *const c_char,
    precision: f64,
) -> *mut c_char {
    let expr: Option<Expr> = from_json_string(expr_json);

    if let Some(e) = expr {
        unsafe {
            if var_ptr.is_null() {
                return std::ptr::null_mut();
            }

            let var_cstr = CStr::from_ptr(var_ptr);

            let var_str = match var_cstr.to_str() {
                | Ok(s) => s,
                | Err(_) => return std::ptr::null_mut(),
            };

            let poly = expr_to_sparse_poly(&e, &[var_str]);

            match isolate_real_roots(&poly, var_str, precision) {
                | Ok(roots) => to_json_string(&roots),
                | Err(_) => std::ptr::null_mut(),
            }
        }
    } else {
        std::ptr::null_mut()
    }
}