Common hashing algorithms in JS

main.js

export function crc32c(data, n = data.length, poly = 0xEDB88320) {
  let crc = 0xFFFFFFFF

  for (let i = 0; i < n; i += 1) {
    crc = crc ^ data.charCodeAt(i)

    for (let j = 0; j < 8; j += 1) {
      crc = crc & 1 ? (crc >>> 1) ^ poly : crc >>> 1
    }
  }

  return crc ^ 0xFFFFFFFF
}

export const CRC_TABLE = Array.from({ length: 256 }, (_, i) => {
  for (let j = 0; j < 8; j += 1) {
    i = (i & 0x01 ? 0xEDB88320 ^ (i >>> 1) : (i >>> 1))
  }

  return i
})

export function crc32(data = "", n = data.length) {
  const crc = data.split("").slice(0, n).reduce((a, b) => {
    const c = b.charCodeAt(0)

    return CRC_TABLE[(c ^ a) & 0xFF] ^ (a >>> 8)
  }, -1)

  return (-1 ^ crc) >>> 0
}

export function adler32(data = "", n = data.length) {
  const MOD_ADLER = 65521

  let a = 1
  let b = 0

  data.slice(0, n).split("").forEach((c) => {
    a = (a + c.charCodeAt(0)) % MOD_ADLER
    b = (b + a) % MOD_ADLER
  })

  return (b << 16) | a
}

export function fletcher16(data, n = data.length) {
  let a = 0
  let b = 0

  data.slice(0, n).split("").forEach((c) => {
    a = (a + c.charCodeAt(0)) % 255
    b = (b + a) % 255
  })

  return (b << 8) | a
}

export function fletcher32(data = "", l = data.length) {
  const encoder = new TextEncoder("utf-8")

  // Round up buffer length if odd to begin with.
  const m = l % 2 === 0 ? l : l + 1

  const buffer = new ArrayBuffer(m)
  const uint8 = new Uint8Array(buffer)
  const uint16 = new Uint16Array(uint8.buffer)

  encoder.encodeInto(data, uint8)

  let c0 = 0
  let c1 = 0

  uint16.forEach((v) => {
    c0 = (c0 + v) % 65535
    c1 = (c1 + c0) % 65535
  })

  return Uint32Array.from([c1 << 16 | c0]).at(-1)
}

test.js

import { adler32, crc32c, crc32, fletcher16, fletcher32 } from "./main.js"

console.assert(crc32c("The quick brown fox jumps over the lazy dog").toString(16) === "414fa339")
console.assert(crc32("The quick brown fox jumps over the lazy dog").toString(16) === "414fa339")

console.assert(adler32("SheetJS") === 176947863)

// https://stackoverflow.com/questions/21496806/fletcher32-is-the-limit-of-360-in-wikipedia-wrong
console.assert("fletcher32", fletcher32("abcde") === 4031760169)
console.assert("fletcher32", fletcher32("abcdef") === 1448095018)
console.assert("fletcher32", fletcher32("abcdefgh") === 3957429649)

console.assert("fletcher32", fletcher32("abcdefgh").toString(16) === 0xEBE19591)
console.assert("fletcher32", fletcher32("abcdef").toString(16) === 0x56502D2A)
console.assert("fletcher32", fletcher32("abcde").toString(16) === "f04fc729")

console.assert(fletcher16("abcde") === 51440)
console.assert(fletcher16("abcdef") === 8279)
console.assert(fletcher16("abcdefgh") === 1575)

console.assert(fletcher16("abcdefgh").toString(16) === "627")
console.assert(fletcher16("abcdef").toString(16) === "2057")
console.assert(fletcher16("abcde").toString(16) === "c8f0")