有效地找到最小和最大

Question

I have two integer parameters a and b . And two integer variables max and min . I want to assign to max the maximum of a and b and to min the minimum of the two. I need to do this operation millions of times and so I want to optimize it. I am currently doing the following:

min = a < b ? a : b;
max = a > b ? a : b;

The problem with this is that it requires two if statements. I am wondering if there is a better way to do this.

Answer 1

std::tie(min, max) = std::minmax(a, b);

Answer 2

if (a < b)
{
    min = a; max = b;
}
else
{
    min = b; max = a;
}

Answer 3

You're probably optimizing prematurely. See what the compiler makes of it.

For a version with just one conditional, this is straightforward:-

if (a < b)
{
  min = a;
  max = b;
}
else
{
  min = b;
  max = a;
}

Answer 4

Or you might want to use some maths:

int absdiff = abs (a-b);
int sum = a+b;
max = (sum+absdiff)/2;
min = (sum-absdiff)/2;

You can trust compilers to optimize all that depending on the base type, you get rid of the branch and get a constant execution time (does not rely on predictors).

Edit:

sample abs integer function on Intel processors :

cdq 
xor eax, edx 
sub eax, edx 

Answer 5

 min=a;max=b;
 if(a>b) {
   max=a;
   min=b;
 } //Here you don't even need an else statement, i don't know how much time does else take but if it does then you have saved it.