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GH-48216: [C++][Parquet] Fix Util Byte Stream Split Internal logic to enable Parquet DB support on s390x #48217

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GH-48216: [C++][Parquet] Fix Util Byte Stream Split Internal logic to enable Parquet DB support on s390x #48217

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67 changes: 40 additions & 27 deletions cpp/src/arrow/util/byte_stream_split_internal.h
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Original file line number Diff line number Diff line change
Expand Up @@ -330,15 +330,20 @@ inline void DoSplitStreams(const uint8_t* src, int width, int64_t nvalues,
while (nvalues >= kBlockSize) {
for (int stream = 0; stream < width; ++stream) {
uint8_t* dest = dest_streams[stream];
#if !ARROW_LITTLE_ENDIAN
const int src_stream = width - 1 - stream;
#else
const int src_stream = stream;
#endif
Comment on lines +333 to +337
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@kou kou Nov 22, 2025

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Could you use

#if ARROW_LITTLE_ENDIAN
  little endian code
#else
  big endian code
#endif

instead of

#if !ARROW_LITTLE_ENDIAN
  big endian code
#else
  little endian code
#endif

for readability. In general, less ! is easier to read.

for (int i = 0; i < kBlockSize; i += 8) {
uint64_t a = src[stream + i * width];
uint64_t b = src[stream + (i + 1) * width];
uint64_t c = src[stream + (i + 2) * width];
uint64_t d = src[stream + (i + 3) * width];
uint64_t e = src[stream + (i + 4) * width];
uint64_t f = src[stream + (i + 5) * width];
uint64_t g = src[stream + (i + 6) * width];
uint64_t h = src[stream + (i + 7) * width];
uint64_t a = src[src_stream + i * width];
uint64_t b = src[src_stream + (i + 1) * width];
uint64_t c = src[src_stream + (i + 2) * width];
uint64_t d = src[src_stream + (i + 3) * width];
uint64_t e = src[src_stream + (i + 4) * width];
uint64_t f = src[src_stream + (i + 5) * width];
uint64_t g = src[src_stream + (i + 6) * width];
uint64_t h = src[src_stream + (i + 7) * width];
#if ARROW_LITTLE_ENDIAN
uint64_t r = a | (b << 8) | (c << 16) | (d << 24) | (e << 32) | (f << 40) |
(g << 48) | (h << 56);
Expand All @@ -357,8 +362,14 @@ inline void DoSplitStreams(const uint8_t* src, int width, int64_t nvalues,
// Epilog
for (int stream = 0; stream < width; ++stream) {
uint8_t* dest = dest_streams[stream];
#if !ARROW_LITTLE_ENDIAN
// On big-endian, reverse byte order: stream 0 gets LSB (at highest address)
const int src_stream = width - 1 - stream;
#else
const int src_stream = stream;
#endif
for (int64_t i = 0; i < nvalues; ++i) {
dest[i] = src[stream + i * width];
dest[i] = src[src_stream + i * width];
}
}
}
Expand All @@ -375,25 +386,22 @@ inline void DoMergeStreams(const uint8_t** src_streams, int width, int64_t nvalu
const uint8_t* src = src_streams[stream];
for (int i = 0; i < kBlockSize; i += 8) {
uint64_t v = arrow::util::SafeLoadAs<uint64_t>(&src[i]);
#if ARROW_LITTLE_ENDIAN
dest[stream + i * width] = static_cast<uint8_t>(v);
dest[stream + (i + 1) * width] = static_cast<uint8_t>(v >> 8);
dest[stream + (i + 2) * width] = static_cast<uint8_t>(v >> 16);
dest[stream + (i + 3) * width] = static_cast<uint8_t>(v >> 24);
dest[stream + (i + 4) * width] = static_cast<uint8_t>(v >> 32);
dest[stream + (i + 5) * width] = static_cast<uint8_t>(v >> 40);
dest[stream + (i + 6) * width] = static_cast<uint8_t>(v >> 48);
dest[stream + (i + 7) * width] = static_cast<uint8_t>(v >> 56);
#if !ARROW_LITTLE_ENDIAN
// Byte-stream-split format stores bytes in little-endian order.
// On big-endian, byteswap after loading and write to reversed stream position.
v = ::arrow::bit_util::ByteSwap(v);
const int dest_stream = width - 1 - stream;
#else
dest[stream + i * width] = static_cast<uint8_t>(v >> 56);
dest[stream + (i + 1) * width] = static_cast<uint8_t>(v >> 48);
dest[stream + (i + 2) * width] = static_cast<uint8_t>(v >> 40);
dest[stream + (i + 3) * width] = static_cast<uint8_t>(v >> 32);
dest[stream + (i + 4) * width] = static_cast<uint8_t>(v >> 24);
dest[stream + (i + 5) * width] = static_cast<uint8_t>(v >> 16);
dest[stream + (i + 6) * width] = static_cast<uint8_t>(v >> 8);
dest[stream + (i + 7) * width] = static_cast<uint8_t>(v);
const int dest_stream = stream;
#endif
dest[dest_stream + i * width] = static_cast<uint8_t>(v);
dest[dest_stream + (i + 1) * width] = static_cast<uint8_t>(v >> 8);
dest[dest_stream + (i + 2) * width] = static_cast<uint8_t>(v >> 16);
dest[dest_stream + (i + 3) * width] = static_cast<uint8_t>(v >> 24);
dest[dest_stream + (i + 4) * width] = static_cast<uint8_t>(v >> 32);
dest[dest_stream + (i + 5) * width] = static_cast<uint8_t>(v >> 40);
dest[dest_stream + (i + 6) * width] = static_cast<uint8_t>(v >> 48);
dest[dest_stream + (i + 7) * width] = static_cast<uint8_t>(v >> 56);
}
src_streams[stream] += kBlockSize;
}
Expand All @@ -404,8 +412,13 @@ inline void DoMergeStreams(const uint8_t** src_streams, int width, int64_t nvalu
// Epilog
for (int stream = 0; stream < width; ++stream) {
const uint8_t* src = src_streams[stream];
#if !ARROW_LITTLE_ENDIAN
const int dest_stream = width - 1 - stream;
#else
const int dest_stream = stream;
#endif
for (int64_t i = 0; i < nvalues; ++i) {
dest[stream + i * width] = src[i];
dest[dest_stream + i * width] = src[i];
}
}
}
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