Selected block-1 length check
Build xxh3_64_pair_check.c, the current standalone program, as described in README.md. This file describes the default (seed-only, default-secret) mode, which is the caveat model for the seeded interfaces; the scored random-secret mode (./check random-secret 20) is described in the README. Arguments of the default mode: [log2 N (1..40), default 20] [stream salt] [M hex] [Mprime hex]; custom messages must both be 32 bytes.
The selected witness seed 2468b3bc26a44073 produces dd686b61e2f6dc69 for both strings. Seed 0 differs. The default salt is 0x2026091901000477.
For 2^20 samples the Xeon observed:
| Length | Collisions | Interpretation |
|---|---|---|
| 16 | not sampled | identical zero prefixes, not a distinct pair |
| 24 | 0 | no finite empirical cap from this smoke run |
| 32 | 725 | selected pair, L = 4 |
| 128 | 725 | block 1 moves to bytes 112..127; same seeded secret words |
Both event-mismatch counts are zero. Full expected output is the actual Xeon output of the new program, despite the retained expected-file name. xxh3_64_32B_check.c is a compatibility entrypoint including the new selected program; the original base-1143 program is retained as historical_base1143_check.c.
The 128-byte extension has L = 16, so the same rate yields a cap two bits higher. Its observations are correlated with the 32-byte run and are not pooled as fresh samples. The three independent upstream confirmation streams recorded with the article, not this smoke sample, supply 2,264,081/(3·2^30) and the 12.47-bit default-secret cap, which the article reports as a caveat beside the scored random-secret result.