commit a6c8e56996c63ce7b0f83c7743a393ecb41c77c6
author Ömer Sinan Ağacan <omersa@google.com> Thu May 15 11:33:46 2025 +0200
committer GitHub <noreply@github.com> Thu May 15 10:33:46 2025 +0100
tree e74ca526e93580f7e96cfa2f3c4919a355dc3402
parent 376c9ce480536ad84572e087e35f31ff931627bc

Improve enum decoding -- alternative (#981)

When decoding an enum value, we call a callback in the enum field's `FieldInfo`. The callback then indexes a map mapping enum numbers to Dart values.

When these conditions hold:

- The known enum numbers are all positive. (so that we can use a list and index it with the number)

- The known enum numbers are more than 70% of the large known enum number. (so that the list won't have a lot of `null` entries, wasting heap space)

We now generate a list instead of a map to map enum numbers to Dart values.

Similar to the map, the list is runtime allocated. No new code generated per message or enum type.

AOT benchmarks:

- Before: `protobuf_PackedEnumDecoding(RunTimeRaw): 47585.14 us.`
- After: `protobuf_PackedEnumDecoding(RunTimeRaw): 38974.566666666666 us.`
- Diff: -18%

Wasm benchmarks:

- Before: `protobuf_PackedEnumDecoding(RunTimeRaw): 52225.0 us.`
- After: `protobuf_PackedEnumDecoding(RunTimeRaw): 34283.33333333333 us.`
- Diff: -34%

**Alternatives considered:**

- #980 uses a map always, but eliminates the `valueOf` closure.
- #985 uses a list always, and does binary search in the list when the list is "shallow".
- #987 is the same as #985, but instead of calling the `valueOf` closure it stores an extra field in `FieldInfo`s for whether to binary search or directly index.

These are all slower than the current PR.