integer division, rounding

Question

There is integer variable, voltage in millivolts.

signed int voltage_mv = 134; //134mV

I have 2-segment display and I want to display hundredths of volts.

How can I convert milivolts to hundredths volts in one operation? Without IF statement, without function?

134 => 13
135 => 14

A short if statement can be made into a ternary operation, ?:. — Alexander Rafferty, Nov 03 '10 at 08:38
134 mV is 0.134 V, not 13 V. What are you trying to do, exactly ? — Paul R, Nov 03 '10 at 08:45
if you want to display a millivolt value in volts, you have to dividie it by 1000. Unless your value is than 1000 mV, the result will be 0 represented as an integer. Are you sure you want to display in Volts? — erelender, Nov 03 '10 at 08:47
sorry about wrong description, I want to display hundredths of volts — Meloun, Nov 03 '10 at 08:52

score 9 · Accepted Answer · answered Nov 03 '10 at 08:33

9

How about simple rounding:

int millivoltToDisplay (int millivolts)
{
  return (millivolts+5)/10;
}

(written as a function for clarity)

answered Nov 03 '10 at 08:33

Nils Pipenbrinck

6

What if the input value is negative ? For correct rounding you need to test for this and subtract 5 rather than add 5, i.e. `return mv >= 0 ? (mv + 5) / 10 : (mv - 5) / 10;` – Paul R Nov 03 '10 at 08:45
to Paul R. - great, thats it! – Meloun Nov 03 '10 at 08:59

score 4 · Answer 2 · edited Jan 31 '20 at 22:29

4

For the same of completeness, if the denominator is odd, then instead of doing:

return (millivolts+denominator/2)/denominator;

you can just have

return (2*millivolts+denominator)/(2*denominator);

and get the correct rounding.

edited Jan 31 '20 at 22:29

Jonathan Leffler

answered Nov 03 '10 at 18:11

Jean-Marc Valin

2 Answers2