perf: fast-path small candid numbers#709
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Encode and decode Nat and Int values through native LEB128 when they fit in machine integers so common small numbers avoid bigint work.
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Mirror the u64-accumulation fast path already added to Nat::decode. Accumulate bits into a u64 with the same overflow guard, then sign-extend at the last byte to produce an i64. Values that fit in i64 skip BigInt allocation entirely; values in [2^63, 2^64-1] (valid Int but not i64) still use BigInt correctly. The BigInt fallback for truly large numbers mirrors the structure of Nat::decode's fallback. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Cover the exact values where the u64 fast path hands off to BigInt: - Nat: u64::MAX (last fast-path value) and u64::MAX+1 (first BigInt), plus a sweep of values near the boundary. - Int: i64::MAX and i64::MAX+1 (positive overflow branch), i64::MIN (sign-extension fast path) and i64::MIN-1 (BigInt negative branch). Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Add inline comments explaining why the `shift < 64` branch must be tested before evaluating `1u64 << (64 - shift)`: the expression would panic in debug mode if shift were >= 64, so the else-false arm acts as both the panic guard and the BigInt-fallback trigger. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
The identical 7-line fits_u64 guard existed verbatim in both Nat::decode and Int::decode. Extract it into a shared inline helper function. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
lwshang
approved these changes
Mar 15, 2026
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Overview
Performance improvement
Requirements
Preserve existing wire compatibility and keep record decoding behavior unchanged.
Solution
Encode and decode Nat and Int values through native LEB128 when they fit in machine integers so common small numbers avoid bigint work.
Considerations
I expect performance improvement and full forward and backward compatibility
Ref. #710