How to round up integer division and have int result in Java

Question

I just wrote a tiny method to count the number of pages for cell phone SMS  I didn t have the option to round up using Math ceil  and honestly it seems to be very ugly   Here is my code   public class Main            param args the command line arguments     public static void main String   args       String message    today we stumbled upon a huge performance leak while optimizing a raycasting algorithm  Much to our surprise  the Math floor   method took almost half of the calculation time  3 floor operations took the same amount of time as one trilinear interpolation  Since we could not belive that the floor-method could produce such a enourmous overhead  we wrote a small test program that reproduce       System out printf  COunt is  d    int messagePageCount message          public static double messagePageCount String message       if message trim   isEmpty      message trim   length      0           return 0        else          if message length    lt   160               return 1            else               return Math ceil  double message length   153                       I don t really like this piece of code and I m looking for a more elegant way of doing this  With this  I m expecting 3 and not 3 0000000  Any ideas

User · Accepted Answer

To round up an integer division you can use

import static java.lang.Math.abs;

public static long roundUp(long num, long divisor) {
    int sign = (num > 0 ? 1 : -1) * (divisor > 0 ? 1 : -1);
    return sign * (abs(num) + abs(divisor) - 1) / abs(divisor);
}

or if both numbers are positive

public static long roundUp(long num, long divisor) {
    return (num + divisor - 1) / divisor;
}

User · Answer

If you want to calculate a divided by b rounded up you can use  a  -a b   b

User · Answer

message length     152    153   This will give a  rounded up  integer

User · Answer

Use Math ceil   and cast the result to int    This is still faster than to avoid doubles by using abs    The result is correct when working with negatives  because -0 999 will be rounded UP to 0   Example     int  Math ceil  double divident   divisor

User · Answer

long numberOfPages   new BigDecimal resultsSize  divide new BigDecimal pageSize   RoundingMode UP  longValue

User · Answer

Google s Guava library handles this in the IntMath class   IntMath divide numerator  divisor  RoundingMode CEILING     Unlike many answers here  it handles negative numbers    It also throws an appropriate exception when attempting to divide by zero

User · Answer

Expanding on Peter s solution  this is what I ve found works for me to always round  towards positive infinity    public static long divideAndRoundUp long num  long divisor        if  num    0    divisor    0    return 0         int sign    num  gt  0   1   -1     divisor  gt  0   1   -1        if  sign  gt  0            return  num   divisor - 1    divisor            else           return  num   divisor

User · Answer

Another one-liner that is not too complicated   private int countNumberOfPages int numberOfObjects  int pageSize        return numberOfObjects   pageSize    numberOfObjects   pageSize    0   0   1       Could use long instead of int  just change the parameter types and return type

User · Answer

this might be helpfull   Subtract the remainder to the legnth and make it a divisible number and then divide it with 153  int r message length   153          Calculate the remainder by  153 return  message length  -r  153      find the pages by adding the remainder and                                      then divide by 153

[java] How to round up integer division and have int result in Java?

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