// Copyright 2018-2025 the Deno authors. MIT license.
// This module is browser compatible.
/**
* Returns the index of the last occurrence of the needle array in the source
* array, or -1 if it is not present.
*
* The complexity of this function is `O(source.length * needle.length)`.
*
* @param source Source array to check.
* @param needle Needle array to check for.
* @param start Start index in the source array to begin the search. Defaults to
* `source.length - 1`.
* @returns Index of the last occurrence of the needle array in the source
* array, or -1 if it is not present.
*
* @example Basic usage
* ```ts
* import { lastIndexOfNeedle } from "@std/bytes/last-index-of-needle";
* import { assertEquals } from "@std/assert";
*
* const source = new Uint8Array([0, 1, 2, 1, 2, 1, 2, 3]);
* const needle = new Uint8Array([1, 2]);
* const notNeedle = new Uint8Array([5, 0]);
*
* assertEquals(lastIndexOfNeedle(source, needle), 5);
* assertEquals(lastIndexOfNeedle(source, notNeedle), -1);
* ```
*
* @example Start index
* ```ts
* import { lastIndexOfNeedle } from "@std/bytes/last-index-of-needle";
* import { assertEquals } from "@std/assert";
*
* const source = new Uint8Array([0, 1, 2, 1, 2, 1, 2, 3]);
* const needle = new Uint8Array([1, 2]);
*
* assertEquals(lastIndexOfNeedle(source, needle, 2), 1);
* assertEquals(lastIndexOfNeedle(source, needle, 6), 5);
* ```
* Defining a start index will begin the search at the specified index in the
* source array.
*/
export function lastIndexOfNeedle(
source: Uint8Array,
needle: Uint8Array,
start: number = source.length - 1,
): number {
if (start < 0) {
return -1;
}
if (start >= source.length) {
start = source.length - 1;
}
const e = needle[needle.length - 1];
for (let i = start; i >= 0; i--) {
if (source[i] !== e) continue;
let matched = 1;
let j = i;
while (
matched < needle.length &&
source[--j] === needle[needle.length - 1 - (i - j)]
) {
matched++;
}
if (matched === needle.length) {
return i - needle.length + 1;
}
}
return -1;
}
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