denoland-deno/std/bytes/mod.ts

// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
import { copyBytes } from "../io/util.ts";

/** Find first index of binary pattern from a. If not found, then return -1 **/
export function findIndex(a: Uint8Array, pat: Uint8Array): number {
  const s = pat[0];
  for (let i = 0; i < a.length; i++) {
    if (a[i] !== s) continue;
    const pin = i;
    let matched = 1,
      j = i;
    while (matched < pat.length) {
      j++;
      if (a[j] !== pat[j - pin]) {
        break;
      }
      matched++;
    }
    if (matched === pat.length) {
      return pin;
    }
  }
  return -1;
}

/** Find last index of binary pattern from a. If not found, then return -1 **/
export function findLastIndex(a: Uint8Array, pat: Uint8Array): number {
  const e = pat[pat.length - 1];
  for (let i = a.length - 1; i >= 0; i--) {
    if (a[i] !== e) continue;
    const pin = i;
    let matched = 1,
      j = i;
    while (matched < pat.length) {
      j--;
      if (a[j] !== pat[pat.length - 1 - (pin - j)]) {
        break;
      }
      matched++;
    }
    if (matched === pat.length) {
      return pin - pat.length + 1;
    }
  }
  return -1;
}

/** Check whether binary arrays are equal to each other **/
export function equal(a: Uint8Array, match: Uint8Array): boolean {
  if (a.length !== match.length) return false;
  for (let i = 0; i < match.length; i++) {
    if (a[i] !== match[i]) return false;
  }
  return true;
}

/** Check whether binary array has binary prefix  **/
export function hasPrefix(a: Uint8Array, prefix: Uint8Array): boolean {
  for (let i = 0, max = prefix.length; i < max; i++) {
    if (a[i] !== prefix[i]) return false;
  }
  return true;
}

/**
 * Repeat bytes. returns a new byte slice consisting of `count` copies of `b`.
 * @param b The origin bytes
 * @param count The count you want to repeat.
 */
export function repeat(b: Uint8Array, count: number): Uint8Array {
  if (count === 0) {
    return new Uint8Array();
  }

  if (count < 0) {
    throw new Error("bytes: negative repeat count");
  } else if ((b.length * count) / count !== b.length) {
    throw new Error("bytes: repeat count causes overflow");
  }

  const int = Math.floor(count);

  if (int !== count) {
    throw new Error("bytes: repeat count must be an integer");
  }

  const nb = new Uint8Array(b.length * count);

  let bp = copyBytes(nb, b);

  for (; bp < nb.length; bp *= 2) {
    copyBytes(nb, nb.slice(0, bp), bp);
  }

  return nb;
}