// Copyright 2018-2025 the Deno authors. MIT license.
// This module is browser compatible.
import { AssertionError } from "./assertion_error.ts";
/**
* Make an assertion that `actual` and `expected` are almost equal numbers
* through a given tolerance. It can be used to take into account IEEE-754
* double-precision floating-point representation limitations. If the values
* are not almost equal then throw.
*
* The default tolerance is one hundred thousandth of a percent of the
* expected value.
*
* @example Usage
* ```ts ignore
* import { assertAlmostEquals } from "@std/assert";
*
* assertAlmostEquals(0.01, 0.02); // Throws
* assertAlmostEquals(1e-8, 1e-9); // Throws
* assertAlmostEquals(1.000000001e-8, 1.000000002e-8); // Doesn't throw
* assertAlmostEquals(0.01, 0.02, 0.1); // Doesn't throw
* assertAlmostEquals(0.1 + 0.2, 0.3, 1e-16); // Doesn't throw
* assertAlmostEquals(0.1 + 0.2, 0.3, 1e-17); // Throws
* ```
*
* @param actual The actual value to compare.
* @param expected The expected value to compare.
* @param tolerance The tolerance to consider the values almost equal. The
* default is one hundred thousandth of a percent of the expected value.
* @param msg The optional message to include in the error.
*/
export function assertAlmostEquals(
actual: number,
expected: number,
tolerance?: number,
msg?: string,
) {
if (Object.is(actual, expected)) {
return;
}
const delta = Math.abs(expected - actual);
if (tolerance === undefined) {
tolerance = isFinite(expected) ? Math.abs(expected * 1e-7) : 1e-7;
}
if (delta <= tolerance) {
return;
}
const msgSuffix = msg ? `: ${msg}` : ".";
const f = (n: number) => Number.isInteger(n) ? n : n.toExponential();
throw new AssertionError(
`Expected actual: "${f(actual)}" to be close to "${f(expected)}": \
delta "${f(delta)}" is greater than "${f(tolerance)}"${msgSuffix}`,
);
}
|