A little toy hash function that maybe works somewhat

hash-ish.js

/* IMPORT */

const crypto = require ( 'crypto' );

/* MAIN */

// const hash = str => {
//   const PRIMEn = 115792089237316195423570985008687907853269984665640564039457584007913129639349n; // 2**256-587 - https://primes.utm.edu/lists/2small/200bit.html
//   const SEEDn = 340282366920938463463374607431768211099n; // 2**128-357 - https://primes.utm.edu/lists/2small/100bit.html

//   const K_BYTES = 16;
//   const K_BITS = K_BYTES * 8;
//   const W_BYTES = K_BYTES * 2;
//   const W_BITS = W_BYTES * 8;

//   const K_BITSn = BigInt ( K_BITS );
//   const W_BITSn = BigInt ( W_BITS );
//   const K_MAXn = ( 2n ** K_BITSn ) - 1n;
//   const W_MAXn = ( 2n ** W_BITSn ) - 1n;
//   const KW_DELTA_BITSn = W_BITSn - K_BITSn;

//   const encoder = new TextEncoder ();
//   const bytes = encoder.encode ( str );
//   const bytesLength = bytes.length;

//   let hash = SEEDn & K_MAXn;

//   for ( let ci = 0, cl = Math.ceil ( bytesLength / K_BYTES ); ci < cl; ci++ ) {
//     let chunk = 0n;
//     for ( let bi = ci * K_BYTES, bl = bi + K_BYTES; bi < bl && bi < bytesLength; bi++ ) {
//       chunk = ( chunk << 8n ) | BigInt ( bytes[bi] );
//     }
//     let input = ( chunk << K_BITSn ) | hash;
//     hash = ( ( input * PRIMEn ) & W_MAXn ) >> KW_DELTA_BITSn;
//   }

//   return hash;
// };






// const hash = str => {
//   const PRIMEn = 18446744073709551437n // 2**64-179 - https://primes.utm.edu/lists/2small/0bit.html
//   const SEEDn = 0n;

//   const K_BYTES = 8;
//   const K_BITS = K_BYTES * 8;
//   const W_BYTES = K_BYTES * 2;
//   const W_BITS = W_BYTES * 8;

//   const K_BITSn = BigInt ( K_BITS );
//   const W_BITSn = BigInt ( W_BITS );
//   const K_MAXn = ( 2n ** K_BITSn ) - 1n;
//   const W_MAXn = ( 2n ** W_BITSn ) - 1n;
//   const KW_DELTA_BITSn = W_BITSn - K_BITSn;

//   const encoder = new TextEncoder ();


//   let bytes = encoder.encode ( str );
//   const bytesLengthAligned = bytes.length + ( ( 8 - ( bytes.length % 8 ) ) % 8 );
//   if ( bytes.length !== bytesLengthAligned ) {
//     const a = new ArrayBuffer ( bytesLengthAligned );
//     const bytes2 = new Uint8Array ( a );
//     bytes2.set ( bytes );
//     bytes = bytes2;
//   }
//   const bytesBigInt = new BigUint64Array ( bytes.buffer );
//   const bytesLength = bytesBigInt.length;

//   let hash = SEEDn & K_MAXn;

//   for ( let bi = 0, bl = bytesLength; bi < bl; bi++ ) {
//     const chunk = bytesBigInt[bi];
//     const input = ( chunk << K_BITSn ) | hash;
//     hash = ( ( input * PRIMEn ) & W_MAXn ) >> KW_DELTA_BITSn;
//   }

//   return hash;
// };









const hash = str => {

  const PRIME = 251; // 2**8-5 - https://primes.utm.edu/lists/2small/0bit.html
  const SEED = 0;

  const K_BYTES = 1;
  const K_BITS = K_BYTES * 8;
  const K_MAX = ( 2 ** K_BITS ) - 1;
  const W_BYTES = K_BYTES * 2;
  const W_BITS = W_BYTES * 8;
  const W_MAX = ( 2 ** W_BITS ) - 1;
  const KW_DELTA_BITS = W_BITS - K_BITS;

  const encoder = new TextEncoder ();

  let bytes = encoder.encode ( str );
  let bytesLength = bytes.length;

  // const bytesLengthAligned = bytes.length + ( ( 8 - ( bytes.length % 8 ) ) % 8 );
  // if ( bytes.length !== bytesLengthAligned ) {
  //   const a = new ArrayBuffer ( bytesLengthAligned );
  //   const bytes2 = new Uint8Array ( a );
  //   bytes2.set ( bytes );
  //   bytes = bytes2;
  // }
  // const bytesBigInt = new BigUint64Array ( bytes.buffer );
  // const bytesLength = bytesBigInt.length;

  let hash = SEED & K_MAX;

  for ( let bi = 0, bl = bytesLength; bi < bl; bi++ ) {
    const chunk = bytes[bi];
    const input = ( chunk << K_BITS ) | hash;
    hash = ( ( input * PRIME ) & W_MAX ) >> KW_DELTA_BITS;
  }

  return hash;
};












/* BENCHMARK */

{ // Hash
  console.time('hash.small');
  const buckets = {};
  const bucketsSize = 1_000_000;
  for ( let i = 0; i < bucketsSize; i++ ) {
    const h = hash ( i.toString ( 32 ) );
    buckets[h] = ( buckets[h] || 0 ) + 1;
  }
  console.log ( `Collisions: ${bucketsSize - Object.values ( buckets ).length}` );
  console.timeEnd('hash.small');
  const big = 'a'.repeat ( 1000000 );
  console.time('hash.big');
  hash ( big );
  console.timeEnd('hash.big');
}

{ // Sha1
  const sha1 = str => crypto.createHash ( 'sha1' ).update ( str ).digest ( 'hex' );
  console.time('sha1');
  const buckets = {};
  const bucketsSize = 1_000_000;
  for ( let i = 0; i < bucketsSize; i++ ) {
    const h = sha1 ( i.toString ( 32 ) );
    buckets[h] = ( buckets[h] || 0 ) + 1;
  }
  console.log ( `Collisions: ${bucketsSize - Object.values ( buckets ).length}` );
  console.timeEnd('sha1');
  const big = 'a'.repeat ( 1000000 );
  console.time('sha1.big');
  sha1 ( big );
  console.timeEnd('sha1.big');
}