hhr293 commented on code in PR #12299:
URL: https://github.com/apache/gluten/pull/12299#discussion_r3412251359
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cpp/core/utils/tac/ffor.hpp:
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@@ -335,15 +343,55 @@ inline constexpr size_t compress64Bound(size_t num) {
return (nBlocks + 1) * kHeaderSize + num * sizeof(uint64_t);
}
+// Encode one block: write header + bit-packed payload into `out`.
+// Returns the number of bytes written. `out` must be 8-byte aligned;
+// callers whose output buffer is unaligned stage through a local scratch.
+// Shared by the 64-bit and 128-bit codecs.
+inline size_t encodeBlock(const uint64_t* src, size_t blockVals, uint64_t*
out) {
+ uint64_t base;
+ unsigned bw;
+ analyze(src, blockVals, base, bw);
+ writeHeader(reinterpret_cast<uint8_t*>(out), static_cast<uint8_t>(bw),
+ static_cast<uint8_t>(blockVals / kLanes), base);
Review Comment:
kMaxValuesPerBlock is 256 and kLanes is 4, so blockVals / kLanes is at most
64 —
well within uint8_t range. All callers cap blockVals to kMaxValuesPerBlock
before calling encodeBlock; this is an invariant enforced by the compress
loop.
No overflow is possible here.
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