translationSourceHash function

String translationSourceHash(String source)

A short, stable, platform-independent hash of source, rendered as 16 hex characters.

Determinism is the whole point — the value must be identical across app launches, Dart/SDK versions, and platforms (native and web), otherwise the same copy would resolve to different storage keys on different devices. It is therefore computed with plain integer arithmetic kept below 2^53 so it is exact on the web (where int is a JS double) rather than relying on String.hashCode (per-run/unstable) or 64-bit bitwise ops (lossy on web).

Two 31-bit polynomial hashes evaluated at different multipliers are combined for ~62 bits of space. The multipliers must differ — with a shared multiplier and only different seeds, h2 - h1 collapses to a length-only constant, so equal-length strings that collide in one half collide in both and the effective strength drops to ~31 bits. Collisions only matter between differing source strings under the same key, so this is comfortably collision-resistant for the purpose.

Do not change this algorithm. Stored <key>@@<hash> entries in every consumer database are addressed by it; changing it orphans them all. It is pinned by a golden test.

Implementation

String translationSourceHash(String source) {
  final bytes = utf8.encode(source);
  final h1 = _polyHash(bytes, 5381, 1000003);
  final h2 = _polyHash(bytes, 52711, 1000033);
  final s1 = h1.toRadixString(16).padLeft(8, '0');
  final s2 = h2.toRadixString(16).padLeft(8, '0');
  return '$s1$s2';
}