不借助第三个临时数交换两个整数,无外乎进行所谓的数字魔术,或借助寄存器实现,但除此外还有一种“巧妙的”方法:通过 XOR 变换实现——不过论其本质,还是所谓的数字魔术,:-) ... 随手测试了下 数字魔术、借助寄存器(纯 Asm 实现) 及 XOR变换 的效率,耗时显示,纯 Asm 实现 < XOR变换 < 数字魔术——结果当然不出意料,纯Asm实现 比另两者快很多。 Delphi 测试代码:program Project1;{$APPTYPE CONSOLE}uses
SysUtils, Windows;var
I, J, K, M, N: Integer;
begin
// the BASE arithmetic ...
M := 1;
N := 2; K := GetTickCount;
for I := 0 to 5000 do
begin
for J := 0 to 5000 do
begin
M := M + N;
N := M - N;
M := M - N;
end;
end;
K := GetTickCount - K;
Writeln(K, ';', M, ';', N);
ReadLn; // use Registers ...
M := 1;
N := 2; K := GetTickCount;
asm // EAX: 循环计数; ECX: I; EDX: J; EBX: M; EDI: N
PUSH EBX
PUSH EDI
MOV EBX, M
MOV EDI, N MOV EAX, 5000
MOV ECX, 0
@Loop1: CMP ECX, EAX
JA @Loop1End
MOV EDX, 0
@Loop2: CMP EDX, EAX
JA @Loop2End
XCHG EBX, EDI
INC EDX
JMP @Loop2
@Loop2End: INC ECX
JMP @Loop1 @Loop1End: MOV M, EBX
MOV N, EDI
POP EDI
POP EBX
end;
K := GetTickCount - K;
Writeln(K, ';', M, ';', N);
ReadLn; // Now XOR ...
M := 1;
N := 2; K := GetTickCount;
for I := 0 to 5000 do
begin
for J := 0 to 5000 do
begin
M := M xor N;
N := N xor M;
M := M xor N;
end;
end;
K := GetTickCount - K;
Writeln(K, ';', M, ';', N);
ReadLn;
end. P.S:以 VC 6.0 + SP6 测试了同样效果的代码,Release 下其结果明显快于 Delphi 的数字魔术(但仍比 纯Asm实现 慢一些) ...Delphi 优化器确实较差,没办法。VC 测试代码:#include <iostream>
#include <windows.h>void main()
{
int I, J, K, M, N;
M = 1;
N = 2;
K = GetTickCount();
for (I = 0; I <= 5000; I++)
{
for (J = 0; J <= 5000; J++)
{
M = M + N;
N = M - N;
M = M - N;
}
}
K = GetTickCount() - K; printf("%d;%d;%d\n", K, M, N);
}另,关于 Delphi 的优化,盒子里的讨论:
http://bbs.2ccc.com/topic.asp?topicid=336505一句话:Delphi Compiler 的优化太差了。
SysUtils, Windows;var
I, J, K, M, N: Integer;
begin
// the BASE arithmetic ...
M := 1;
N := 2; K := GetTickCount;
for I := 0 to 5000 do
begin
for J := 0 to 5000 do
begin
M := M + N;
N := M - N;
M := M - N;
end;
end;
K := GetTickCount - K;
Writeln(K, ';', M, ';', N);
ReadLn; // use Registers ...
M := 1;
N := 2; K := GetTickCount;
asm // EAX: 循环计数; ECX: I; EDX: J; EBX: M; EDI: N
PUSH EBX
PUSH EDI
MOV EBX, M
MOV EDI, N MOV EAX, 5000
MOV ECX, 0
@Loop1: CMP ECX, EAX
JA @Loop1End
MOV EDX, 0
@Loop2: CMP EDX, EAX
JA @Loop2End
XCHG EBX, EDI
INC EDX
JMP @Loop2
@Loop2End: INC ECX
JMP @Loop1 @Loop1End: MOV M, EBX
MOV N, EDI
POP EDI
POP EBX
end;
K := GetTickCount - K;
Writeln(K, ';', M, ';', N);
ReadLn; // Now XOR ...
M := 1;
N := 2; K := GetTickCount;
for I := 0 to 5000 do
begin
for J := 0 to 5000 do
begin
M := M xor N;
N := N xor M;
M := M xor N;
end;
end;
K := GetTickCount - K;
Writeln(K, ';', M, ';', N);
ReadLn;
end. P.S:以 VC 6.0 + SP6 测试了同样效果的代码,Release 下其结果明显快于 Delphi 的数字魔术(但仍比 纯Asm实现 慢一些) ...Delphi 优化器确实较差,没办法。VC 测试代码:#include <iostream>
#include <windows.h>void main()
{
int I, J, K, M, N;
M = 1;
N = 2;
K = GetTickCount();
for (I = 0; I <= 5000; I++)
{
for (J = 0; J <= 5000; J++)
{
M = M + N;
N = M - N;
M = M - N;
}
}
K = GetTickCount() - K; printf("%d;%d;%d\n", K, M, N);
}另,关于 Delphi 的优化,盒子里的讨论:
http://bbs.2ccc.com/topic.asp?topicid=336505一句话:Delphi Compiler 的优化太差了。
咱甚至反汇编过 Delphi 和 VC 的(都是优化全开后生成的)控制台程序,唉,结果相当让人沮丧,Delphi 的优化器不是一般的差。
大家可以自己试试。
你写个
tmp=a;
a=b;
b=tmp;
他也不知道你是干啥啊你觉得ASM快,可以嵌进去嘛
不是相当简单嘛,数字游戏而已
var
a,b: integer;
t: dword;
begin
t := GetTickCount;
a := 3;
b := 5;
a := a + b;
b := a - b;
a := a - b;
ShowMessage('用时:'+inttostr(GetTickCount - t));
ShowMessage(IntToStr(a));
ShowMessage(IntToStr(b));
end;