[ARROW-2622] [C++] Array methods IsNull and IsValid are not complementary

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.9.0
• Fix Version/s: 0.10.0
• Component/s: C++
• External issue URL: https://github.com/apache/arrow/issues/15721
• Assignee: Antoine Pitrou
• Reporter: Thomas Buhrmann
• Created: 21/May/18 17:03
• Updated: 11/Jan/23 07:22
• Resolved: 06/Feb/19 14:48

Description

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:

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);
}

Which leads to a situation where in the case of non-allocated bitmaps values are neither Null nor Valid. Shouldn't it rather be:

bool IsValid(int64_t i) const {
  return null_bitmap_data_ == NULLPTR ||
    BitUtil::GetBit(null_bitmap_data_, i + data_->offset);
}

?

Issue Links

• is superceded by: ARROW-2641 [C++] Investigate spurious memset() calls