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fix: req_sketch truncated k to 8 bits - #552
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Thanks, i fixed failure of ci. Can you rebase?
The constructor computed k_ with std::max<uint8_t>, so any k of 256 or more wrapped around: req_sketch<float>(256).get_k() returned 4 and req_sketch<float>(500).get_k() returned 244. k is a uint16_t everywhere else (the parameter, the member and the serialized format), and the documented range is [4, 1024], so use std::max<uint16_t>. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Validate the original constructor argument before allocating compactors so k = 1025 cannot round down into the supported range. Preserve existing lower-bound clamping and odd-k rounding, and document the constructor behavior. Cover both accuracy modes, the upper boundary, values above the limit, and the maximum uint16_t value. Verified the new regression fails before the fix and all 17 CTest targets pass on the EC2 ARM64 host with GCC 14.2.1.
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req_sketch's constructor computesk_withstd::max<uint8_t>, so anykof 256 or more wraps around:Everything else already treats
kas 16 bits: the constructor parameter, thek_member and the serialized format. The documented range (and the Java implementation's check) is [4, 1024]. This changes the onestd::max<uint8_t>tostd::max<uint16_t>; odd values still round down.Added a test,
req sketch: k above 255. It checks k of 256, 500 and 1024, an odd k (1001 → 1000), and that k = 1024 survives serialization in estimation mode. Without the fix it fails with4 == 256. With it, all REQ tests pass.We found this through the DuckDB DataSketches extension, where users asking for K = 1024 were silently getting K = 4.
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