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[jira] [Created] (ARROW-2622) [C++] Array methods IsNull and IsValid are not complementary


Thomas Buhrmann created ARROW-2622:
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             Summary: [C++] Array methods IsNull and IsValid are not complementary
                 Key: ARROW-2622
                 URL: https://issues.apache.org/jira/browse/ARROW-2622
             Project: Apache Arrow
          Issue Type: Bug
          Components: C++
    Affects Versions: 0.9.0
            Reporter: Thomas Buhrmann


Hi, not sure if this is a bug or if I misinterpret the spec. According to the latter, "Arrays having a 0 null count may choose to not allocate the null bitmap". From this I'd infer that the statement also holds in the other direction, i.e. non-allocated bitmaps imply a 0 null count. This would mean that if a bitmap is not allocated, IsValid() should always return true. But at the moment it's doing this:
{code:java}
bool IsNull(int64_t i) const {
  return null_bitmap_data_ != NULLPTR &&
    BitUtil::BitNotSet(null_bitmap_data_, i + data_->offset);
}

bool IsValid(int64_t i) const {
  return null_bitmap_data_ != NULLPTR &&
    BitUtil::GetBit(null_bitmap_data_, i + data_->offset);
}
{code}
Which leads to a situation where in the case of non-allocated bitmaps values are neither Null nor Valid. Shouldn't it rather be:
{code:java}
bool IsValid(int64_t i) const {
  return null_bitmap_data_ == NULLPTR ||
    BitUtil::GetBit(null_bitmap_data_, i + data_->offset);
}{code}
?



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