The fastest two-digit exchange in C Language

Self carrying: http://hi.baidu.com/evergreen19/blog/item/dbc1d5f13241c3a5a50f5245.html

Recently started writing, RC4, because a lot of swap is required, so the swapAlgorithmEfficiency has a significant impact on the overall speed of RC4, so we have summarized some good exchange algorithms to share with you.

Int A = 5, B = 7;

Method 1: inline assembly, using the stack zone --Swapping containers

_ ASM {

Push

Push B

Pop

Pop B

}

Method 2: Use the exclusive or operation

A = a ^ B;

B = a ^ B;

A = a ^ B;

Or written:

A ^ = B;

B ^ =;

A ^ = B;

Method 3: Addition Switching

A = A + B;

B = A-B;

A = A-B;

Method 2 and 3 are the same:

Using the nature of inverse functions, functionsC = f (a, B), There must be an inverse function,A = g (C, B );

In this way, you can use

A = f (a, B );

B = g (A, B );

A = g (A, B );

Three-Step exchange of two numbers

Method 4: UseXchgCommand---Use special commands (Dedicated instructions)

_ ASM {

MoV eax,

Xchg eax, B

MoV A, eax

}

However, the Register size must be used, for example:

1,16BitCPUThe data registers include:(Ax,BX,CXAndDX)

2,32BitCPUThe data registers include:(Eax,EBX,ECXAndEDX)