Livt.ML

src/storage/RamLookupTable.lvt

namespace Livt.ML.Storage

using Livt.IO

/**
 * A bounded view of externally owned RAM; no implicit table initialization.
 */
component RamLookupTable<ENTRIES: int, STORAGE: IRam<int>> : ILookupTable
{
	static assert ENTRIES > 0, "table length must be positive"

	// Borrowed word-addressed memory and table base offset.
	storage: STORAGE
	base: int

	/**
	 * Borrows externally initialized word-addressed storage and records the base offset. No
	 * table data is allocated or loaded.
	 */
	new(storage: STORAGE, base: int)
	{
		this.storage = storage
		this.base = base
	}

	/**
	 * Returns ENTRIES when the full word span is addressable, otherwise zero. Assumes a
	 * contiguous memory address range.
	 */
	override fn Length() int
	{
		if (base < 0 || base > 2147483647 - ENTRIES) {
			return 0
		}

		if (!storage.IsValidAddress(base) || !storage.IsValidAddress(base + ENTRIES - 1)) {
			return 0
		}

		return ENTRIES
	}

	/**
	 * Returns the stored integer at the table-relative index, or zero for an invalid index or
	 * unavailable span.
	 */
	override fn Read(index: int) int
	{
		var available = this.Length()

		if (index < 0 || index >= available) {
			return 0
		}

		return storage.Read(base + index)
	}
}