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Posted to jira@arrow.apache.org by "Niranda Perera (Jira)" <ji...@apache.org> on 2021/07/12 17:20:00 UTC
[jira] [Updated] (ARROW-13312) [C++] Bitmap::VisitWordAndWrite
epilogue needs to work on Words (not bytes)
[ https://issues.apache.org/jira/browse/ARROW-13312?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Niranda Perera updated ARROW-13312:
-----------------------------------
Description:
In recently added `Bitmap::VisitWordAndWrite` method, translates the `visitor` lambda (that works on a `Word`) to a byte-visitor while handling the epilogue.
This could lead to incorrect results in the client code.
ex:
{code:java}
// code placeholder
// N readers, M writers
int64_t bits_written = 0;
auto visitor = [&](std::array<Word, N> in, std::array<Word, M>* out){
...
bits_written += (sizeof(Word) * 8);
}{code}
At the end of the Visit, bits_written would have an incorrect sum because in the prologue, it adds 64 to bits_written for each trailing byte, whereas it should've been 8.
Possible solution:
Needs to add ReadTrailingWord and WriteTrailingWord functionality to BitmapWordReader and BitmapWordWriter respectively and call visitor with the words in the prologue.
was:
In recently added `Bitmap::VisitWordAndWrite` method, translates the `visitor` lambda (that works on a `Word`) to a byte-visitor while handling the prologue.
This could lead to incorrect results in the client code.
ex:
{code:java}
// code placeholder
// N readers, M writers
int64_t bits_written = 0;
auto visitor = [&](std::array<Word, N> in, std::array<Word, M>* out){
...
bits_written += (sizeof(Word) * 8);
}{code}
At the end of the Visit, bits_written would have an incorrect sum because in the prologue, it adds 64 to bits_written for each trailing byte, whereas it should've been 8.
Possible solution:
Needs to add ReadTrailingWord and WriteTrailingWord functionality to BitmapWordReader and BitmapWordWriter respectively and call visitor with the words in the prologue.
> [C++] Bitmap::VisitWordAndWrite epilogue needs to work on Words (not bytes)
> ---------------------------------------------------------------------------
>
> Key: ARROW-13312
> URL: https://issues.apache.org/jira/browse/ARROW-13312
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C++
> Reporter: Niranda Perera
> Priority: Major
>
> In recently added `Bitmap::VisitWordAndWrite` method, translates the `visitor` lambda (that works on a `Word`) to a byte-visitor while handling the epilogue.
> This could lead to incorrect results in the client code.
> ex:
> {code:java}
> // code placeholder
> // N readers, M writers
> int64_t bits_written = 0;
> auto visitor = [&](std::array<Word, N> in, std::array<Word, M>* out){
> ...
> bits_written += (sizeof(Word) * 8);
> }{code}
> At the end of the Visit, bits_written would have an incorrect sum because in the prologue, it adds 64 to bits_written for each trailing byte, whereas it should've been 8.
>
> Possible solution:
> Needs to add ReadTrailingWord and WriteTrailingWord functionality to BitmapWordReader and BitmapWordWriter respectively and call visitor with the words in the prologue.
>
>
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