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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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65 changes: 39 additions & 26 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 = stream;
#else
const int src_stream = width - 1 - stream;
#endif
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
const int src_stream = stream;
#else
// On big-endian, reverse byte order: stream 0 gets LSB (at highest address)
const int src_stream = width - 1 - 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 @@ -376,24 +387,21 @@ inline void DoMergeStreams(const uint8_t** src_streams, int width, int64_t nvalu
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);
const int dest_stream = stream;
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@kiszk kiszk Nov 27, 2025

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Is it better to move const int ... for both endians to line 387? While a compiler may move it in the current code, it is sure to move it in the source code.

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@Vishwanatha-HD Vishwanatha-HD Nov 29, 2025 •
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@kiszk If I move this const int to line 387, then I wont be able to assign the value to this variable. Basically we wont be able to modify the value of the const variable once again.. The declaration and assignment should happen together & only once for const variables..

error: assignment of read-only variable ‘dst_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);
// 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;
#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 = stream;
#else
const int dest_stream = width - 1 - 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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