wgtmac commented on code in PR #49960:
URL: https://github.com/apache/arrow/pull/49960#discussion_r3224845392
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cpp/src/arrow/util/byte_stream_split_internal.h:
##########
@@ -421,14 +421,28 @@ void ByteStreamSplitEncodeScalar(const uint8_t*
raw_values, int width,
DoSplitStreams(raw_values, kNumStreams, num_values, dest_streams.data());
}
+// If changing this value, please check that TestByteStreamSplitLargeWidth
still
+// exercises the slow path.
+constexpr inline int kByteStreamSplitMaxTemporaryAlloc = 8192;
+
inline void ByteStreamSplitEncodeScalarDynamic(const uint8_t* raw_values, int
width,
const int64_t num_values,
uint8_t* out) {
- ::arrow::internal::SmallVector<uint8_t*, 16> dest_streams;
- dest_streams.resize(width);
- for (int stream = 0; stream < width; ++stream) {
- dest_streams[stream] = &out[stream * num_values];
+ if (ARROW_PREDICT_TRUE(width < kByteStreamSplitMaxTemporaryAlloc / 8)) {
+ ::arrow::internal::SmallVector<uint8_t*, 32> dest_streams;
Review Comment:
Why the small vector size is changed to 32 here but
ByteStreamSplitDecodeScalarDynamic still uses 16?
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