tonyroberts commented on code in PR #50843:
URL: https://github.com/apache/arrow/pull/50843#discussion_r3756971368
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cpp/src/arrow/type.h:
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@@ -196,6 +197,22 @@ class ARROW_EXPORT DataType : public
std::enable_shared_from_this<DataType>,
/// subclasses of FixedWidthType
virtual int bit_width() const { return -1; }
+ /// \brief Returns the number of bytes needed to store `num_elements`
+ /// values of this fixed-width type, rounding up for bit-packed types
+ /// (e.g. boolean) that use less than one byte per value. Returns -1
+ /// for non-fixed-width types, and should only be used for subclasses
+ /// of FixedWidthType
+ virtual int64_t bytes_required(int64_t num_elements) const {
Review Comment:
I just found `util::internal::PreallocateFixedWidthArrayData`, that seems
like the right thing to use here, and avoids adding a new method or doing
`bit_util::BytesForBits(length * bit_width)`.
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