import { expect, test } from "vitest";
import { lerp, lerpPrecice } from "./lerp.ts";

test("lerp", () => {
	const a = 0;
	const b = 0.1;

	expect(lerp(a, b, 0.2)).toBe(0.020000000000000004);
	expect(lerp(a, b, 0.5)).toBe(0.05);
});

test("lerpPrecice", () => {
	const a = 0;
	const b = 0.1;

	expect(lerpPrecice(a, b, 0.2)).toBe(0.020000000000000004);
	expect(lerpPrecice(a, b, 0.5)).toBe(0.05);
});

test("lerp vs lerpPrecice", () => {
	// a and b with very different magnitudes expose
	// catastrophic cancellation in lerp's `(b - a)` term
	const a = 1e16;
	const b = 1;

	// lerp loses b at t = 1
	expect(lerp(a, b, 1)).toBe(0);

	// lerpPrecice keeps b at t = 1
	expect(lerpPrecice(a, b, 1)).toBe(b);

	expect(lerp(a, b, 0)).toBe(a);
	expect(lerpPrecice(a, b, 0)).toBe(a);
});