Performance of If-else if tree vs. Switch (multiple variables) in C#

Jure

C#If-else if treeIf-else if tree vs. Switch (multiple variables) in C#Switch (multiple variables) in C#

5 Comments

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FireMyst12y ago
This is a good article. I like how you laid out the code, It would be better too if you did benchmark tests against all three constructs like this blog: http://cc.davelozinski.com/c-sharp/what-is-the-fastest-conditional-statement I've personally found the nested switch/case statements slower than their if/else equivalents.
lgsalamon16y ago
try this : static void newswitchtest() { Stopwatch timer; timer = Stopwatch.StartNew(); timer.Stop(); int bin; timer.Start(); for (int i = 0; i < 100000000; ++i) { for (int a = 0; a < 2; ++a) { for (int b = 0; b < 2; ++b) { for (int c = 0; c < 2; ++c) { bin = a + (b << 1) + (c << 2); switch (bin) { case 0: break; case 1: break; case 2: break; case 3: break; case 4: break; case 5: break; case 6: break; case 7: break; } } } } } timer.Stop(); Console.WriteLine(timer.ElapsedMilliseconds.ToString()); } My tests : 9704 ms if/else 8251 ms switch 5817 ms the code above Good article.
- Jure16y agoedited
  Thanks for the reply! The only problem with that is that first you have convert n-choice variable to [0, n-1] interval, then shift the value - which is what conditional operator (?) does in one step without performing any arithmetic or bitwise operations with values, but simply by checking the values against certain criteria. For example, two variables below can't use shift operators: int apples = 12 // number of apples - ternary (few, moderate, a lot) bool mature = false // is eatable? - binary (true, false) int situation = (apples < 5 ? 0 : (apples <= 10 ? 1 : 2)) + (mature ? 3 : 0); switch(situation) { case 0: // few uneatable apples case 1: // moderate number of uneatable apples case 2: // a lot of uneatable apples ---> this get's executed case 3: // few tasty apples case 4: // moderate number of tasty apples case 5: // a lot of tasty apples }
Sam Hobbs16y ago
Another possibility would be to create an array of methods using a delegate type and then instead of using a switch, just index into the array. That could be quite efficient if there are more than 3 conditions, right?
- Jure16y ago
  Good thinking. The performance isn't that good, though, if-tree was quite faster when I tested it. Of course I called the delegate methods in the if-tree too. The reason must be in addition. If-tree checks 3 values, then calls appropriate method, while the array of delegate-methods has to check values and calculate the index too. BIG advantage is far less code, and clarity, also easy to maintain. I will definitely use array of delegates from now on, unless I have to make the program repeat the checking a whole bunch of times, like I did when testing. Thanks for the comment!

Recently I was writing a program with 3 binary values and I had to handle all 8 possible "situations" and switch is said to be faster, because it uses an indexed branch table. However, it accepts only one value, while I had 3 different values to check.

I've come up with a little trick to store all 8 possible situations into one single integer value:

switch ((a == 1 ? 1 : 0) + (b == 1 ? 2 : 0) + (c == 1 ? 4 : 0))
{

case 0: break; //none true
case 1: break; //a true
case 2: break; //b true
case 3: break; //a and b true
case 4: break; //c true
case 5: break; //a and c true
case 6: break; //b and c true
case 7: break; //all true
}

The mathematical formula for each variable:

n: numeral system base [2, ∞]
m: zero-based index of the checked variable [0, ∞]
v: zero-based index of the variable's value [0, n - 1]

result for one variable = nm * v

As an example, 3 ternary variables:

int situation = (a == 0 ? 0 : (a == 1 ? 1 : 2)) + (b == 0 ? 0 : (b == 1 ? 3 : 6)) + (c == 0 ? 0 : (c == 1 ? 9 : 18));

The switch above has to (in every case) get-and-check 4 times (3 times in the calculation, 1 time to match a case). However, it also has to perform the addition.

So, is switch in this case faster? I have tested switch's performance (every single situation 100,000,000 times) against the following if-else if trees:

1. The obvious one:

if (a == 1 && b == 1 && c == 1) ;
else if (a == 1 && b == 1) ;
else if (a == 1 && c == 1) ;
else if (b == 1 && c == 1) ;
else if (a == 1) ;
else if (b == 1) ;
else if (c == 1) ;
else ;

Condition	Num of checks	Check sequence
a & b & c	3	a,b,c
a & b	5	a,b,c,a,b
a & c	6	a,b,a,b,a,c
b & c	5	a,a,a,b,c
a	8	a,b,a,b,a,c,a
b	8	a,a,a,b,c,a,b
c	8	a,a,a,b,a,b,c
none	8	a,a,a,b,a,b,

Average: 6.375 checks

Switch/if-tree ratio:

calculation into a variable first: 9/10
calculation straight into switch: 3/4

Switch is faster.

My testing code:

int counter = 0;
Timer timer = new Timer(1);
timer.Elapsed += (object o, ElapsedEventArgs e) =>
{
++counter;
};

timer.Start();
for (int i = 0; i < 100000000; ++i)
{
for (int a = 0; a < 2; ++a)
{
for (int b = 0; b < 2; ++b)
{
for (int c = 0; c < 2; ++c)
{
if (a == 1 && b == 1 && c == 1) ;
else if (a == 1 && b == 1) ;
else if (a == 1 && c == 1) ;
else if (b == 1 && c == 1) ;
else if (a == 1) ;
else if (b == 1) ;
else if (c == 1) ;
else ;
}
}
}
}
timer.Stop();
Console.WriteLine(counter.ToString());

counter = 0;
timer.Start();
for (int i = 0; i < 100000000; ++i)
{
for (int a = 0; a < 2; ++a)
{
for (int b = 0; b < 2; ++b)
{
for (int c = 0; c < 2; ++c)
{
switch ((a == 1 ? 1 : 0) +
(b == 1 ? 2 : 0) +
(c == 1 ? 4 : 0))
{
case 0: break;
case 1: break;
case 2: break;
case 3: break;
case 4: break;
case 5: break;
case 6: break;
case 7: break;
}
}
}
}
}
timer.Stop();
Console.WriteLine(counter.ToString());

2. Dual-check/single-check:

if (a && b)
{
if (c) ;
else ;
}
else if (a && c) ;
else if (b && c) ;
else if (a) ;
else if (b) ;
else if (c) ;
else ;

Condition	Num of checks	Check sequence
a & b & c	3	a,b,c
a & b	3	a,b,c,
a & c	4	a,b,a,c
b & c	5	a,a,a,b,c
a	6	a,b,a,c,b,a
b	6	a,a,b,c,a,b
c	6	a,a,b,a,b,c
none	6	a,a,b,a,b,c

Average: 4.875 checks

Switch/if-tree ratio:

calculation into a variable first: 18/17
calculation straight into switch: 1/1

Same speed unless you use a separate variable.

3. Single-check:

if (a)
{
if (b)
{
if (c) ;
else ;
}
else if (c) ;
else ;
}
else if (b)
{
if (c) ;
else ;
}
else if (c) ;
else ;

Condition	Num of checks	Check sequence
a	3	a,b,c
a & b	3	a,b,c,
a & b & c	3	a,b,c
a & c	3	a,b,c
b	3	a,b,c
b & c	3	a,b,c
c	3	a,b,c
none	3	a,b,c

Average: 3 checks

Switch/if-tree ratio:

calculation into a variable first: 14/9
calculation straight into switch: 3/2

If-else if tree is quite faster. This is expected, because it makes 3 checks, while switch makes 4.

4. What if we make the switch nested too?

switch (a)
{
case 0:
switch (b)
{
case 0:
switch (c)
{
case 0: break; // none
case 1: break; // c
}
break;
case 1:
switch (c)
{

case 0: break; // b
case 1: break; // b & c
}
break;
}
break;
case 1:
switch (b)
{
case 0:
switch (c)
{
case 0: break; // a
case 1: break; // a & c
}
break;
case 1:
switch (c)
{
case 0: break; // a & b
case 1: break; // a & b & c
}
break;
}
break;
}

Switch/if-tree ratio: 15/14

If-else if tree still slightly faster.

All these ratios were very consistent, average relative mistake was 0.6%.

Conclusion:

If you want to make your code clear, then it's perhaps better to use a switch statement. But don't forget to add comments to each case about which situation it represents.

If clarity is not an issue, use "Single-check" if-else if tree.

Thanks for reading, code safely!