riverdelta/std/rt.nil

// Start the heap at 1024. In practice this could probably be as low as we want.
// TODO: The compiler should set this global to whatever it has calculated the heap
// start to be. But well, 1024 ought to be enough for now. lol.
global HEAD_PTR: I32 = 1024_I32;

// Every struct has a header of an I32 as a refcount.

// Allocate a new item. We do not deallocate anything yet.
// lol.
function allocateItem(objSize: I32, align: I32): I32 = (
    if align < 4_I32 then std.abort("invalid alignment");

    // Include the refcount header.
    let actualSize = 4_I32 + objSize;

    // Let's see whether we can fit the refcount into the align bits.
    // I happen to know that everything will always be at least 4 bytes aligned.
    let alignedPtr = std.alignUp(HEAD_PTR, align);
    let actualObjPtr = if (alignedPtr - HEAD_PTR) > align then (
        alignedPtr - 4_I32
    ) else (
        // Take up the next spot.
        alignedPtr + align - 4_I32
    );

    let newHeadPtr = actualObjPtr + actualSize;

    if newHeadPtr > __memory_size() then (
        // 16 pages, very arbitrary.
        let result = __memory_grow(16_I32);
        // If allocation failed we get -1. We don't have negative numbers yet, lol.
        if result > 4294967295_I32 then (
            std.abort("failed to grow memory");
        );
    );

    actualObjPtr
);