[GitHub] [arrow] jorgecarleitao edited a comment on pull request #8645: ARROW-10561: [Rust] Simplified Buffer's `write` and `write_bytes` and fixed undefined behavior

[GitBox <gi...@apache.org>]

jorgecarleitao edited a comment on pull request #8645:
URL: https://github.com/apache/arrow/pull/8645#issuecomment-726510728


   Ok, I confirm that this error is due to a wrong pointer offset on the `set_bits_raw` and that this undefined behavior is already present in `master`:
   
   ```
   Switched to branch 'master'
   Your branch is up to date with 'upstream/master'.
      Compiling arrow v3.0.0-SNAPSHOT (/Users/jorgecarleitao/projects/arrow/rust/arrow)
       Finished bench [optimized] target(s) in 53.79s
        Running /Users/jorgecarleitao/projects/arrow/rust/target/release/deps/builder-65ece1c06584e62c
   Gnuplot not found, using plotters backend
   bench_primitive         time:   [522.83 us 523.58 us 524.34 us]                            
                           thrpt:  [7.4499 GiB/s 7.4607 GiB/s 7.4713 GiB/s]
                    change:
                           time:   [-6.7844% -4.8815% -3.0463%] (p = 0.00 < 0.05)
                           thrpt:  [+3.1420% +5.1320% +7.2782%]
                           Performance has improved.
   Found 9 outliers among 100 measurements (9.00%)
     3 (3.00%) high mild
     6 (6.00%) high severe
   
   Benchmarking bench_bool: Warming up for 3.0000 serror: process didn't exit successfully: `/Users/jorgecarleitao/projects/arrow/rust/target/release/deps/builder-65ece1c06584e62c --bench` (signal: 11, SIGSEGV: invalid memory reference)
   ```
   
   This PR removes now also removes that function altogether and replaces it by a safe counterpart. I suspect that there will be a performance regression, but I do not know enough of bit operations to be able to fix the function (and it is not clear whether we should, as per @vertexclique suggestion of using `bitvec`).


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