perf(de): inline LEB128 and add map fast paths#722
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Four decode-side optimizations, all behavior-preserving: 1. Nat/Int deserialization bypass: for values fitting u64/i64, read LEB128 directly and call visitor.visit_u64/i64, avoiding the BigUint/BigInt → bytes → BigUint round-trip (saves 3 allocations per value). 2. BigNum vector fast path: batch cost tracking and skip per-element type cloning/checking for Vec<Nat>, Vec<Int>, and Vec<Int> with Nat wire type, mirroring the existing primitive vec fast path. 3. PrimitiveVecAccess with IntoDeserializer: on LE platforms, decode primitive vectors via a lightweight SeqAccess that reads directly from the input byte slice using serde's IntoDeserializer, bypassing the full Deserializer and Cursor overhead. 4. Borrowed string deserialization: use visit_borrowed_str instead of copying bytes, enabling zero-copy for &str targets. Benchmark improvements (decode, vs previous optimized baseline): vec_nat: 910M → 300M (-67%) vec_nat32: 406M → 247M (-39%) vec_nat64: 411M → 255M (-38%) vec_int16: 411M → 251M (-39%) btreemap: 13.3B → 11.2B (-16%) option_list: 23M → 18M (-20%) variant_list: 21M → 17M (-21%) Made-with: Cursor
### Motivation - Remove external `binary_parser` dependency for hot deserialization paths. ### Solution - Inline LEB128 u64/i64, length, and bool reading directly in `Deserializer`. - Add `text_fast_path` flag to skip type checks when key types are known during map deserialization. - Apply fast path to map keys/values and bignum handling. ### Meta - Removed unused `BoolValue` import.
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…st paths Introduce `try_read_leb_u64` and `try_read_leb_i64` returning `Ok(None)` on overflow and `Err` on genuine I/O errors (e.g. unexpected EOF). The bignum fallback callers in `deserialize_int` and `deserialize_nat` now use these, so a truncated input correctly surfaces an error rather than silently falling through to a secondary bignum decode failure. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
- Keep inlined LEB128/bool/len readers and map fast paths from PR - Keep try_read_leb_* error-propagation fix - Take master's deserialize_string -> deserialize_str delegation - Take master's PrimitiveVecAccess cursor fix (advance by access.offset) - Take master's SeqAccess expect/wire_type assignment and if !is_fast restructure Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
lwshang
approved these changes
Mar 18, 2026
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Motivation
binary_parserdependency for hot deserialization paths.Solution
Deserializer.text_fast_pathflag to skip type checks when key types are known during map deserialization.Meta
BoolValueimport.