prtkgaur commented on code in PR #48345:
URL: https://github.com/apache/arrow/pull/48345#discussion_r3921390201
##########
cpp/src/parquet/decoder.cc:
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@@ -2372,6 +2375,130 @@ class ByteStreamSplitDecoder<FLBAType> : public
ByteStreamSplitDecoderBase<FLBAT
}
};
+// ----------------------------------------------------------------------
+// ALP decoder (Adaptive Lossless floating-Point)
+
+template <typename DType>
+class AlpDecoder : public TypedDecoderImpl<DType> {
+ public:
+ using Base = TypedDecoderImpl<DType>;
+ using T = typename DType::c_type;
+
+ // TODO: support incremental decode. Partial reads currently decode the
entire
Review Comment:
Agreed, and done. `VectorReader` validates the header and the whole offset
chain once in `Open` and then decodes any single vector on demand, so `Decode`
is `Open` plus a loop and both paths share one validator instead of having one
each — a few lines longer than the whole-page version rather than shorter.
A vector entered at its first value and read to its end decodes straight
into the caller's buffer; anything else goes through one vector of scratch. So
the decoder holds 4 or 8 KB rather than a page, pool-backed and allocated on
first use — which also answers your scratch-buffer comment.
`TestAlpEncoding.BatchedDecode` covers six batch plans over a 2000-value page.
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