With a high level of confidence, I would agree that this is a Sinhalese mahout knife. I have/had two examples for comparison. An early variation and a much later one, both from Mandarin Mansion. Peter does a very good job of the breakdown of these so I will include his link as well for reference.
https://www.the-mansfield-collection...a-mahout-knife
https://www.the-mansfield-collection...a-mahout-knife
https://www.mandarinmansion.com/item...-kirichchiya-0
Geoffrey