how to generate minecraft hex digests

test.js

var crypto = require('crypto');
var assert = require('assert');

function mcHexDigest(str) {
  var hash = new Buffer(crypto.createHash('sha1').update(str).digest(), 'binary');
  // check for negative hashes
  var negative = hash.readInt8(0) < 0;
  if (negative) performTwosCompliment(hash);
  var digest = hash.toString('hex');
  // trim leading zeroes
  digest = digest.replace(/^0+/g, '');
  if (negative) digest = '-' + digest;
  return digest;

}

function performTwosCompliment(buffer) {
  var carry = true;
  var i, newByte, value;
  for (i = buffer.length - 1; i >= 0; --i) {
    value = buffer.readUInt8(i);
    newByte = ~value & 0xff;
    if (carry) {
      carry = newByte === 0xff;
      buffer.writeUInt8(newByte + 1, i);
    } else {
      buffer.writeUInt8(newByte, i);
    }
  }
}

assert.strictEqual(mcHexDigest('Notch'), "4ed1f46bbe04bc756bcb17c0c7ce3e4632f06a48");
assert.strictEqual(mcHexDigest('jeb_'), "-7c9d5b0044c130109a5d7b5fb5c317c02b4e28c1");
assert.strictEqual(mcHexDigest('simon'), "88e16a1019277b15d58faf0541e11910eb756f6");

This is much simpler using modern javascript:

function hexDigest(text) {
  const hash = crypto.createHash("sha1")
    .update(text)
    .digest()

  return BigInt.asIntN( // performs two's compliment
    160,           // hash size in bits
    hash.reduce(   // convert buffer to bigint using reduce
      (a, x) =>
        a << 8n |  // bit-shift the accumulator 8 bits (one byte) to the left
        BigInt(x), // fill lower byte just freed up by bit-shifting using bitwise or-operator
      0n           // start with accumulator value of 0
    )
  ).toString(16)   // display the result with base 16 (hex)
}