Rounding

Version 0.33: This article is up to date for the latest stable release of Dungeon Crawl Stone Soup.

Crawl uses several types of rounding:

• Always round up: Numbers are rounded up.
• Always round down (truncate): Numbers are rounded down, thus ignoring the decimal place. By default, C++ truncates numbers, so if there's no other indication in the code, it'll be rounded down.
• Round half up: 0.5 and up are rounded up, else round down. This may be used for ranges and other numbers that can't feasibly be randomised.
• Weighted rounding (rounded in a weighted manner): The number is tracked, typically to the hundredths place. The decimal place remainder is the % chance to round up. This is very commonly used to avoid hard breakpoints, e.g., spell damage, shield encumbrance, time used to take actions, AC/EV all use weighted rounding.
  • For example, if you would take 4.30 aut to move, you instead have a 30% chance to move at 5 aut, and a (100%-30%=) 70% chance to move at 4 aut.
  • If you have 35.5 AC, for each hit, there is a 50% chance for your AC to be treated as 35, and a 50% chance for your AC to be treated as 36.

History

In general, as the versions progressed, more and more things started to use random rounding. For example, AC and EV weren't randomly rounded until 0.32.