mapleFU commented on code in PR #36183:
URL: https://github.com/apache/arrow/pull/36183#discussion_r1236910039
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cpp/src/parquet/encoding.cc:
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@@ -2189,7 +2193,13 @@ void DeltaBitPackEncoder<DType>::Put(const T* src, int
num_values) {
// making subtraction operations well-defined and correct even in case of
overflow.
// Encoded integers will wrap back around on decoding.
// See http://en.wikipedia.org/wiki/Modular_arithmetic#Integers_modulo_n
- deltas_[values_current_block_] = value - current_value_;
+ UT delta = value - current_value_;
+ //update blocks minimum delta
+ if(delta < min_delta_) min_delta_ = delta;
+ //calculate which block a maximum delta belongs to -> whole number division
+ const uint32_t
miniblock_index{values_current_block_/values_per_mini_block_};
+ if(delta > max_deltas_[miniblock_index])max_deltas_[miniblock_index] =
delta;
Review Comment:
After that `FlushBlock` is called, should `max_deltas_` being set to 0?
Seems that previous block's max will be bring into next block?
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cpp/src/parquet/encoding.cc:
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@@ -2163,6 +2164,8 @@ class DeltaBitPackEncoder : public EncoderImpl, virtual
public TypedEncoder<DTyp
uint32_t total_value_count_{0};
UT first_value_{0};
UT current_value_{0};
+ UT min_delta_;
Review Comment:
should it default as UT::max ?
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