[ARROW-16223] BasicDecimal128::ReduceScaleBy with rounding works incorrectly

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 8.0.0
• Component/s: C++
• Labels: pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/20195
• Assignee: Yibo Cai
• Reporter: Renat Valiullin
• Created: 19/Apr/22 01:40
• Updated: 11/Jan/23 11:42
• Resolved: 19/Apr/22 15:18

Description

BasicDecimal128 one(5); // 0.5
one.ReduceScaleBy(1, true); // expected 1, but result is -1 

BasicDecimal128 BasicDecimal128::ReduceScaleBy(int32_t reduce_by, bool round) const {
  ...    
  if (remainder.Abs() >= divisor_half) { 
    if (result > 0) { // should be >=
      result += 1; 
    } 
    else {
      result -= 1;
    } 
  }

 

Issue Links

• links to: GitHub Pull Request #12917