Binary operatos

[topnik1]

What is faster :
if(x==y) //numbers are equal
or
if(!x^y) //numbers are equal

?

[MiiNiPaa]

Any sane compiler will optimize both snippets to the same code.

But you should never write code like in your second snippet.

Martin Fowler wrote:

Any fool can write code that a computer can understand. Good programmers write code that humans can understand.

Always code as if the person who ends up maintaining your code is a violent psychopath who knows where you live.

[topnik1]

Good reply.

[MiiNiPaa]

To prove my first statement: decompiled code as on GCC 4.8.1 with -O2 optimizations:

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__attribute__((noinline)) bool f1(int x, int y) { return (x==y); } __attribute__((noinline)) bool f2(int x, int y) { return !(x^y); }

0x00401520 cmp %edx,%ecx 0x00401522 sete %al 0x00401525 retq 0x00401530 cmp %edx,%ecx 0x00401532 sete %al 0x00401535 retq

[Cubbi]

Same here on IBM (compiler xlc 12)

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.f1__FiT1: subf r0,r4,r3 cntlzw r0,r0 rlwinm r3,r0,27,5,31 bclr BO_ALWAYS,CR0_LT

.f2__FiT1: xor r0,r3,r4 # okay, there is a small diff here cntlzw r0,r0 rlwinm r3,r0,27,5,31 bclr BO_ALWAYS,CR0_LT

(with gcc on the same platform, it used xor for both functions)

and on a sparc: (compiler studio 12.3)

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__1cCf16Fii_b_: xor %o0,%o1,%o5 srl %o5,0,%o4 sub %g0,%o4,%o3 srlx %o3,63,%o2 xor %o2,1,%g5 retl ! Result = %o0 and %g5,255,%o0

__1cCf26Fii_b_: xor %o0,%o1,%o5 srl %o5,0,%o4 sub %g0,%o4,%o3 srlx %o3,63,%o2 xor %o2,1,%g5 retl ! Result = %o0 and %g5,255,%o0

[stefke1998]

faster is EXAMPLE:

if(a == b)
{
//Function
}