Finding absolute value of a number without using Math abs

Question

Is there any way to find the absolute value of a number without using the Math abs   method in java

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Although this shouldn t be a bottle neck as branching issues on modern processors isn t normally a problem  but in the case of integers you could go for a branch-less solution as outlined here  http   graphics stanford edu  seander bithacks html IntegerAbs    x    x  gt  gt  31      x  gt  gt  31     This does fail in the obvious case of Integer MIN VALUE however  so this is a use at your own risk solution

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If you look inside Math abs you can probably find the best answer    Eg  for floats                 Returns the absolute value of a   code float  value         If the argument is not negative  the argument is returned         If the argument is negative  the negation of the argument is returned         Special cases          lt ul gt  lt li gt If the argument is positive zero or negative zero  the        result is positive zero          lt li gt If the argument is infinite  the result is positive infinity          lt li gt If the argument is NaN  the result is NaN  lt  ul gt         In other words  the result is the same as the value of the expression          lt p gt   code Float intBitsToFloat 0x7fffffff  amp  Float floatToIntBits a                   param   a   the argument whose absolute value is to be determined         return  the absolute value of the argument              public static float abs float a            return  a  lt   0 0F    0 0F - a   a

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Since Java is a statically typed language  I would expect that a abs-method which takes an int returns an int  if it expects a float returns a float  for a Double  return a Double  Maybe it could return always the boxed or unboxed type for doubles and Doubles and so on    So you need one method per type  but now you have a new problem  For byte  short  int  long the range for negative values is 1 bigger than for positive values    So what should be returned for the method   byte abs  byte in           todo     If the user calls abs on -128  You could always return the next bigger type so that the range is guaranteed to fit to all possible input values  This will lead to problems for long  where no normal bigger type exists  and make the user always cast the value down after testing - maybe a hassle    The second option is to throw an arithmetic exception  This will prevent casting and checking the return type for situations where the input is known to be limited  such that X MIN VALUE can t happen  Think of MONTH  represented as int    byte abs  byte in  throws ArithmeticException      if  in    Byte MIN VALUE  throw new ArithmeticException   abs called on Byte MIN VALUE        return  in  lt  0     byte  -in   in       The  let s ignore the rare cases of MIN VALUE  habit is not an option  First make the code work - then make it fast  If the user needs a faster  but buggy solution  he should write it himself   The simplest solution that might work means  simple  but not too simple   Since the code doesn t rely on state  the method can and should be made static  This allows for a quick test    public static void main  String args           System out println  abs new Byte    7          System out println  abs new Byte   -7          System out println  abs  byte   7        System out println  abs  byte  -7        System out println  abs new Byte    127          try               System out println  abs new Byte   -128                catch  ArithmeticException ae                System out println   Integer      Math abs  new Integer   -128                System out println  abs  byte   127        System out println  abs  byte  -128        I catch the first exception and let it run into the second  just for demonstration   There is a bad habit in programming  which is that programmers care much more for fast than for correct code  What a pity     If you re curious why there is one more negative than positive value  I have a diagram for you

User · Answer

In case of the absolute value of an integer x without using Math abs    conditions or bit-wise operations  below could be a possible solution in Java     int    long x x - 1   double x   1     Because Java treats a b as a - a b   b  the sign of the result will be same as  a  no matter what sign of  b  is   x x-1  x will equal abs x -1  type casting of  long  is to prevent overflow and double allows dividing by zero   Again  x   Integer MIN VALUE will cause overflow due to subtracting 1

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Use the class Math  Math abs num

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Like this   if  number  lt  0        number    -1

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-num  will equal to num for  Integer MIN VALUE  as   Integer MIN VALUE    Integer MIN VALUE   -1

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You can use    abs num    num  lt  0    -num   num

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Yes   abs number    number  lt  0    -number   number    For integers  this works fine  except for Integer MIN VALUE  whose absolute value cannot be represented as an int    For floating-point numbers  things are more subtle  For example  this method -- and all other methods posted thus far -- won t handle the negative zero correctly   To avoid having to deal with such subtleties yourself  my advice would be to stick to Math abs

User · Answer

Here is a one-line solution that will return the absolute value of a number   abs number    num  lt  0    -num   num

[java] Finding absolute value of a number without using Math.abs()

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