Trial Division Primality in C#

using System;
// Trial Division Primality in C#
//
// PURPOSE
// A composite integer has a factor no larger than its square root. Trial division checks
// only candidate divisors up to that bound.
//
// METHOD
// Reject values below two, handle two, and reject other even values. Test odd divisors until
// d exceeds n/d, which avoids computing d squared.
//
// COMPLEXITY
// O(sqrt(n)) time and O(1) auxiliary space.
//
// CONTRACT
// Returns 1 for prime, 0 otherwise. This is suitable for small integers, not large
// cryptographic candidates.
// Public APIs infer array lengths except in C, which accepts pointer/length pairs. Vertex
// counts and matrix dimensions remain explicit. Arrays must contain signed 32-bit integers.
// Sorted order, correct tree topology, and caller-owned data-structure invariants are
// preconditions; checking them on every query would change query complexity.
// Scalar and shape checks are included. Value-range checks are included where needed to
// prevent invalid indexing or nontermination. Allocation sizes are capped at 4,000,000
// workspace entries. Arithmetic outside Python raises an error on 32-bit overflow; Python
// uses arbitrary precision. Native allocation failures propagate. In-place outputs may be
// partly updated after arithmetic failure. These are single-threaded, in-memory
// implementations.
//
// LANGUAGE DETAILS
// C# / .NET 10: ReadOnlySpan<int> inputs, Span<int> outputs, primitive workspace arrays,
// Array.BinarySearch for LIS, and checked integer arithmetic. Invalid arguments and overflow
// throw exceptions.
//
// EXAMPLE
// Expected return: 1.
// Run: Use Program.cs in a net10.0 console project; dotnet run.
// Tests for this exact source artifact run before publication. The accompanying source
// archive includes unit cases, runtime results, and source hashes.

class Program {
    static void alg_require(bool valid) { if (!valid) throw new ArgumentException("invalid algorithm input"); }
    static int alg_size(int n) { alg_require(n>=0 && n<=4000000); return n; }

    static int is_prime(int n) {
        checked {
            if ((n < 2)) {
                return 0;
            }
            if ((n == 2)) {
                return 1;
            }
            if (((n % 2) == 0)) {
                return 0;
            }
            int d = 3;
            while ((d <= (n / d))) {
                if (((n % d) == 0)) {
                    return 0;
                }
                d = (d + 2);
            }
            return 1;
        }
    }

    static void Main() {
        int n = 97;
        int result = is_prime(n);
        Console.WriteLine(result);
    }
}