First of all, ||
and &&
are short-circuit. Which mean that in:
if(a || b || c)
DoSomething();
if a
is true, b
and c
will not be evaluated.
Secondly, your implementation of the ||
is false:
if(a)
DoSomething();
if(b)
DoSomething();
if(c)
DoSomething();
DoSomething()
will be called up to 3 times.
It should be:
if(a)
DoSomething();
else if(b)
DoSomething();
else if(c)
DoSomething();
To finish, if you want performance prefer shorter call first in your conditions:
if(aShortFunctionToExecute() || aVeryVeryLongFunctionToExecute())
DoSomething();
Will be faster than
if(aVeryVeryLongFunctionToExecute() || aShortFunctionToExecute())
DoSomething();
Because of lazy-evaluation
If you disassemble the code of:
private static void Main()
{
if (a() && b() && c())
{
Console.WriteLine("DoSomething");
}
}
bool a(){
return true;
}
bool b(){
return 3 % 2 == 1;
}
bool c(){
return (3 % 2) / 1 == 1;
}
You'll get:
if (a() && b() && c())
00000022 call FFFFFFFFFFEE8D90
00000027 mov byte ptr [rbp+20h],al
0000002a movzx eax,byte ptr [rbp+20h]
0000002e test eax,eax
00000030 je 000000000000005A
00000032 call FFFFFFFFFFEE8D98
00000037 mov byte ptr [rbp+21h],al
0000003a movzx eax,byte ptr [rbp+21h]
0000003e test eax,eax
00000040 je 000000000000005A
00000042 call FFFFFFFFFFEE8DA0
00000047 mov byte ptr [rbp+22h],al
0000004a movzx ecx,byte ptr [rbp+22h]
0000004e xor eax,eax
00000050 test ecx,ecx
00000052 sete al
00000055 mov dword ptr [rbp+24h],eax
00000058 jmp 0000000000000062
0000005a nop
0000005b mov dword ptr [rbp+24h],1
00000062 nop
00000063 movzx eax,byte ptr [rbp+24h]
00000067 mov byte ptr [rbp+2Fh],al
0000006a movzx eax,byte ptr [rbp+2Fh]
0000006e test eax,eax
00000070 jne 0000000000000087
{
00000072 nop
Console.WriteLine("DoSomething");
00000073 mov rcx,12603398h
0000007d mov rcx,qword ptr [rcx]
00000080 call 00000000577A82A0
00000085 nop
}
and for the code:
private static void Main()
{
if (a())
if(b())
if(c())
Console.WriteLine("DoSomething");
}
static bool a(){
return true;
}
static bool b(){
return 3 % 2 == 1;
}
static bool c(){
return (3 % 2) / 1 == 1;
}
You'll get:
if (a())
00000022 call FFFFFFFFFFEE8D90
00000027 mov byte ptr [rbp+20h],al
0000002a movzx ecx,byte ptr [rbp+20h]
0000002e xor eax,eax
00000030 test ecx,ecx
00000032 sete al
00000035 mov dword ptr [rbp+24h],eax
00000038 movzx eax,byte ptr [rbp+24h]
0000003c mov byte ptr [rbp+3Fh],al
0000003f movzx eax,byte ptr [rbp+3Fh]
00000043 test eax,eax
00000045 jne 00000000000000A4
if(b())
00000047 call FFFFFFFFFFEE8D98
0000004c mov byte ptr [rbp+28h],al
0000004f movzx ecx,byte ptr [rbp+28h]
00000053 xor eax,eax
00000055 test ecx,ecx
00000057 sete al
0000005a mov dword ptr [rbp+2Ch],eax
0000005d movzx eax,byte ptr [rbp+2Ch]
00000061 mov byte ptr [rbp+3Fh],al
00000064 movzx eax,byte ptr [rbp+3Fh]
00000068 test eax,eax
0000006a jne 00000000000000A4
if(c())
0000006c call FFFFFFFFFFEE8DA0
00000071 mov byte ptr [rbp+30h],al
00000074 movzx ecx,byte ptr [rbp+30h]
00000078 xor eax,eax
0000007a test ecx,ecx
0000007c sete al
0000007f mov dword ptr [rbp+34h],eax
00000082 movzx eax,byte ptr [rbp+34h]
00000086 mov byte ptr [rbp+3Fh],al
00000089 movzx eax,byte ptr [rbp+3Fh]
0000008d test eax,eax
0000008f jne 00000000000000A4
Console.WriteLine("DoSomething");
00000091 mov rcx,125D3398h
0000009b mov rcx,qword ptr [rcx]
0000009e call 00000000577B82A0
000000a3 nop
Which is a bit longer: it takes 40 instructions instead of 31.
As pointed out by thanosqr, the performance also depend of the probability for your condition to be true. To take his example:
If a
fails 99% of the time and take 1 sec to run and if b
succeed 99% of the time and take 10 sec to run, over 100 tries you'll be faster putting b
first:
if(b || a) => 10s 99% ==> 100 runs will take 99*10+11 = 1001s
if(b || a) => 11s 1%
if(a || b) => 11s 99% ==> 100 runs will take 99*11+1 = 1090s
if(a || b) => 1s 1%
Also, I suggest you this reading " Why is it faster to process a sorted array than an unsorted array? " which is quite interesting!