Round numbers to any decimal place

[sergeevabc]

Let's say there is a file, it takes up 12 350 976 bytes, I want to see how much it is in megabytes (or, I guess, you call it mebibytes now), but at the same time round it to the nearest tenths or hundredths.

$ qalc 12 350 976/1024/1024
(12350976 / 1024) / 1024 = approx. 11.77880859

$ qalc some_magic_command(12 350 976/1024/1024)
11.8

[hanna-kn]

$ qalc "round(12 350 976/1024/1024, 1)"
round((12350976 / 1024) / 1024, 1) = 59/5 = 11 + 4/5 = 11.8

$ qalc -s "maxdeci 1" 12 350 976/1024/1024
(12350976 / 1024) / 1024 ≈ 11.8

$ qalc -s "maxdeci 1" 12 350 976B to MiB
12350976 bytes ≈ 11.8 MiB

$ qalc "round(12 350 976/mebi, 1)"
round((12350976 / 1024) / 1024, 1) = 59/5 = 11 + 4/5 = 11.8

[sergeevabc]

Here's a weird case when looking for the difference between dates in days.

$ ver && qalc --version
Microsoft Windows [Version 6.1.7601]
5.5.2

$ qalc -t days(now, 2022-12-22T13:54)
906.6906192   <-- days are usually integers, not fractions

$ qalc -t -s maxdeci 0 days(now, 2022-12-22T13:54)
0   <-- aggrrhh

$ qalc -t -s 'maxdeci 0' days(now, 2022-12-22T13:54)
Did you mean "maxdeci" (max decimals)?   <-- yes!

$ qalc -t -s "maxdeci 0" days(now, 2022-12-22T13:54)
907   <-- what?! 906 is expected

[hanna-kn]

The failure when using single quotes is an anomaly of the command prompt (it works in PowerShell).

Why should the days be rounded downwards? The number of days between 2022-12-22 and 2025-06-16 is exactly 907.

If you want to use a different rounding method than the default (round towards nearest integer), either use the rounding option (e.g. qalc -t -s "rounding down; maxdeci 0" "days(now, 2022-12-22T13:54)") or one of the rounding functions (e.g. qalc -t "floor(days(now, 2022-12-22T13:54))").

[sergeevabc]

Why should the days be rounded downwards?

Are days really the kind of value that people tend to round one way or the other? We can say that the day has just begun (morning), half of it has passed (lunch), or most of it has passed (evening), but it is still the same day. And only at midnight, as in the Cinderella tale, we are free to say the day is over.

There are indeed 907 days between 2022-12-22 00:00 and 2025-06-16 00:00, but it was no accident that I used now instead of today for the first date and specified the exact time for the second date. That's why qalc said 906.6906192, not 907. That is, the specified period did not reach the end of the day. So I used the -s "maxdeci 0" to remove everything after the point, but it turned out to not only truncate, but also round, although it's not that obvious from its name.