Hacker News Reader

It's done in JavaScript because there is not integer type. (Ok, ok, nowadays there is bigint, but historically.) So you do all int like calculations with number (which is IEEE double), but be sure to only do arithmetic where the result is still an integer. That's why you end up using a double as a numeric key. And I think a double can basically hold a 53 bit integer exactly.

View on HN

This is definitely not my area of expertise, but my understanding was that the mantissa was actually the source of inexactness in floats? I know the power bits (10 bits?) are pretty close to actual twos complement ints, and you could always do things in a C-like union, but I wasn't aware you could directly treat the mantissa like an int

Ok, that's different then. Using integers as keys should not be a problem, even if they are stored as floats. Problems start if you use non-integers or IEEE special values as keys.

Reply on news.ycombinator.com