When duration is around 1E3 or 1E6 micros
printf("%6.2F", 999.995) gives 1000.00 which is 7 digits

So printf rounds float arguments, it looks like we first need to do that rounding before we know how many digits there are, so we can choose the correct unit.

I imagine printing a float value with sprintf and reading it back with sscanf should do the trick, though there may be more modern solutions.

I imagine printing a float value with sprintf and reading it back with sscanf should do the trick, though there may be more modern solutions.

snprintf with size 0 string would return the number of characters needed for the print.
That is snprintf(0, 0, "%6.2F", 999.995) => 7; snprintf(0, 0, "%6.2F", 999.994) => 6.

I implement it as a check for (>= 1000 and >= 999995) because get_unit takes int64_t, and in master, the only values that trigger the %6.2F overflow are

• 1000, 1000000 (because of the use of > instead of >=)
• 999995 to 999999 (because of rounding)

There isn't a 1000.00 secs problem because we switch to 15.00 mins after 900.00 secs.

Nice I didn't know that about snprintf.

I can see now why this is sufficient, merged with thanks!