"%.1f" of 999.99 => "999.0"

[NicholasWMRitchie]

Incorrect rounding of floating point numbers:

sprintf!("%.1f",999.99).unwrap() == "999.0"

should be "1000.0"

[NicholasWMRitchie]

I can't run the tests on Windows but..
I'd add tests for %f and %g:

check_fmt("%.1f",9.99);
check_fmt("%.1e",9.99);

I suspect the problem is the use of n.trunc() rather than n.round() on lines 314 & 332.

[tjol]

Well spotted! I don't think just replacing trunc with round will work (that'll probably turn 1.5 into 1.5 or something), but you're on the right track

[NicholasWMRitchie]

Of course, you are correct. round(...) replacing trunc(...) won't fix it.
Maybe, rounding the number to the correct number of decimal places above trunc(...) might.