Rounding to significant digits doesn't work as expected

[hniksic]

Let's say I want to round the number to three significant digits, rounding away from zero:

fn round3up(d: Decimal) -> Decimal {
    d.round_sf_with_strategy(3, RoundingStrategy::AwayFromZero).unwrap()
}

I would expect the following assertions to hold:

assert_eq!("12400", round3up("12301".parse().unwrap()).to_string());
assert_eq!("124", round3up("123.01".parse().unwrap()).to_string());
assert_eq!("1.24", round3up("1.2301".parse().unwrap()).to_string());
assert_eq!("0.124", round3up("0.12301".parse().unwrap()).to_string());

However, only the last assertion actually passes. round3up("12301") results in 12310, round3up("123.01") in 123.1, and round3up("1.2301") in 1.231. If I reduce the first argument of round_sf_with_strategy() to 2, then the first three assertions pass, but the last one doesn't, resulting in (correct) 0.13.

Am I misunderstanding the meaning of "significant digits" in the context of round_sf_with_strategy()? How would one implement consistent rounding to three significant digits?

[paupino]

You're correct in thinking something doesn't look right. I'm in transit the next couple of days but will attempt to dig into this issue this weekend to see what's going on. Will keep you posted.