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 0.33.