Hash

The save file format never stores field names. Each entry is identified only by a 32-bit hash.

Algorithm

Field names are hashed with Murmur3 x86 32-bit using seed 0 and the UTF-8 encoding of the name.

For reference, the constants the game uses are:

• c1 = 0xCC9E2D51
• c2 = 0x1B873593
• Block rotate 15, mix rotate 13, mix multiplier 5, mix constant 0xE6546B64
• Finalizer multipliers 0x85EBCA6B and 0xC2B2AE35, shift 16 / 13 / 16

TypeScript reference implementation

This is the implementation ltdsave.app uses itself, lifted verbatim from src/lib/sav/hash.ts.

const C1 = 0xcc9e2d51;
const C2 = 0x1b873593;

export function murmur3_x86_32(input: string, seed = 0): number {
  const bytes = new TextEncoder().encode(input);
  return murmur3_x86_32_bytes(bytes, seed);
}

export function murmur3_x86_32_bytes(bytes: Uint8Array, seed = 0): number {
  const len = bytes.length;
  const nBlocks = (len / 4) | 0;
  let h1 = seed >>> 0;

  for (let i = 0; i < nBlocks; i++) {
    const o = i * 4;
    let k1 = (bytes[o] | (bytes[o + 1] << 8) | (bytes[o + 2] << 16) | (bytes[o + 3] << 24)) >>> 0;
    k1 = Math.imul(k1, C1);
    k1 = (k1 << 15) | (k1 >>> 17);
    k1 = Math.imul(k1, C2);

    h1 ^= k1;
    h1 = (h1 << 13) | (h1 >>> 19);
    h1 = (Math.imul(h1, 5) + 0xe6546b64) | 0;
  }

  let k1 = 0;
  const tail = nBlocks * 4;
  switch (len & 3) {
    case 3:
      k1 ^= bytes[tail + 2] << 16;
    // fallthrough
    case 2:
      k1 ^= bytes[tail + 1] << 8;
    // fallthrough
    case 1:
      k1 ^= bytes[tail];
      k1 = Math.imul(k1, C1);
      k1 = (k1 << 15) | (k1 >>> 17);
      k1 = Math.imul(k1, C2);
      h1 ^= k1;
  }

  h1 ^= len;
  h1 ^= h1 >>> 16;
  h1 = Math.imul(h1, 0x85ebca6b);
  h1 ^= h1 >>> 13;
  h1 = Math.imul(h1, 0xc2b2ae35);
  h1 ^= h1 >>> 16;
  return h1 >>> 0;
}

Collisions

Every name in the save schema produces a distinct hash. There are no known collisions.