~bigbes/tarantool-protobuf: 6d0ec7bf

wire: decode wins — utf8.len validator + fast paths + FFI cast

Five focused decode optimizations, all in wire.lua, landing a 3.9-6.6x
speedup on bench/bench.lua decode and matching wins on lazy / shapes
benches. Per-helper numbers from bench/wire_bench.lua:

  is_valid_utf8(32B ASCII):  545 ns -> 36 ns  (15x)
  is_valid_utf8(1KB ASCII): 16329 ns -> 539 ns (30x)
  decode_string(32B):         140 ns -> 80 ns  (1.75x)
  decode_double:              299 ns -> 226 ns (1.32x)
  decode_fixed64:             196 ns -> 184 ns (1.07x)

1. utf8.len swap. Pure-Lua RFC 3629 validator replaced by
   `utf8.len(s) ~= nil` (ICU U8_NEXT-backed at src/lua/utf8.c:165).
   Source-verified to reject every proto3 case: stray continuation,
   overlong, surrogates, truncated, > U+10FFFF, 5-byte+ sequences.
   Conformance suite still at 1478/1478 expected passes.

2. decode_string / decode_bytes 1-byte LEN fast path. Strings <=127
   bytes (the RPC common case) skip two function-call layers
   (decode_string -> decode_len -> decode_varint).

3. decode_float / decode_double via ffi.cast(uint8_t*, buf) instead
   of buf:sub. Eliminates the per-call string-slice allocation.

4. decode_double Inf/NaN check via a uint32[2] union split. Bit ops
   on Lua numbers don't allocate; the previous uint64 cdata path
   produced 3+ intermediates per call.

5. decode_fixed64 reads via the new pb_u64_u_t union (ffi.copy +
   read .u). Replaces UINT64(lo) + bit.lshift(UINT64(hi), 32) which
   allocated 2-3 cdata per call.

All FFI cdef/union locals hoisted to the top of the file so the
fixed-width decoders all reference the same scratch buffers.

497/497 luatest pass.  19/19 jit-trace gates pass.  Conformance
(binary + text) shows zero unexpected failures.

Eugene Blikh <bigbes@gmail.com> — 2026-05-16 14:43:24 UTC

Commit 6d0ec7bf3b4e1a051bc75efee59c9cd3d5ed3f04 — view raw patch

Parent(s): e53089dd

1 changed file(s)

FileStatus+−
runtime/pb/wire.lua M +79 -69