std/bytes/index_of_needle.ts

// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.

/** Returns the index of the first occurrence of the needle array in the source
 * array, or -1 if it is not present.
 *
 * A start index can be specified as the third argument that begins the search
 * at that given index. The start index defaults to the start of the array.
 *
 * The complexity of this function is O(source.length * needle.length).
 *
 * ```ts
 * import { indexOfNeedle } from "https://deno.land/std@$STD_VERSION/bytes/index_of_needle.ts";
 * const source = new Uint8Array([0, 1, 2, 1, 2, 1, 2, 3]);
 * const needle = new Uint8Array([1, 2]);
 * console.log(indexOfNeedle(source, needle)); // 1
 * console.log(indexOfNeedle(source, needle, 2)); // 3
 * ```
 */
export function indexOfNeedle(
  source: Uint8Array,
  needle: Uint8Array,
  start = 0,
): number {
  if (start >= source.length) {
    return -1;
  }
  if (start < 0) {
    start = Math.max(0, source.length + start);
  }
  const s = needle[0];
  for (let i = start; i < source.length; i++) {
    if (source[i] !== s) continue;
    const pin = i;
    let matched = 1;
    let j = i;
    while (matched < needle.length) {
      j++;
      if (source[j] !== needle[j - pin]) {
        break;
      }
      matched++;
    }
    if (matched === needle.length) {
      return pin;
    }
  }
  return -1;
}