我有这段代码可以访问有关“x”和“y”轴上的点的一些信息。此信息稍后用于在屏幕上绘制一些点。这就是代码的工作方式：
//MAX_X_COORD has a value of 169
//MAX_Y_COORD has a value of 55
void RedrawFromDATAtable()
{
COORD pos;
HANDLE tmpbuf = CreateConsoleScreenBuffer(GENERIC_WRITE , NULL, NULL, CONSOLE_TEXTMODE_BUFFER, NULL);
WriteConsoleA(tmpbuf, " ", 1, NULL, NULL);
if(SetConsoleActiveScreenBuffer(tmpbuf)==0)
{MessageBoxA(NULL, "ERROR", "ERROR", 0);return;}
bufferdata_ex * dptr;
//bufferdata_ex * y_dptr;
int * lcol(new int); //Increases speed by reducing function calls - Experienced about twice as fast drawing!
for(short x=0;x<MAX_X_COORD;x++)
{
//y_dptr = bridge->DATA[x];
for(short y=0;y<MAX_Y_COORD;y++)
{
//dptr = (y_dptr+y); //Rewrite to use a constant pointer!
dptr = &(_bridge->DATA[x][y]);
if(dptr->InUse==true)
{
{
pos.X = x;
pos.Y = y;
SetConsoleCursorPosition(output, pos);
//haschanged = false;
}
if(!(*lcol==dptr->color)) //Need for a new color?
{ SetConsoleTextAttribute(output, dptr->color);lcol = &dptr->color;}
char c((char)dptr->sym);
WriteConsoleA(output, &c, 1, NULL, NULL);
lcol = &dptr->color;
}
}
}
SetConsoleTextAttribute(output, bridge->current_color);
SetConsoleCursorPosition(output, last_mouse_position);
SetConsoleActiveScreenBuffer(output);
CloseHandle(tmpbuf);
delete lcol;
}
切入正题！
好吧！所以最近我想到这样访问数组会减慢我的代码速度。据我所知，每当您访问数组中的元素时，处理器都会获取数组的基址，然后将元素的大小乘以用于查找指定元素地址的索引。我的想法是，如果我多次要求处理器执行此操作，而不是仅仅创建一个指向地址的指针，然后使用它来处理我的元素，那么它会减慢我的代码速度。所以我将代码重写为以下内容：
void RedrawFromDATAtable()
{
COORD pos;
HANDLE tmpbuf = CreateConsoleScreenBuffer(GENERIC_WRITE , NULL, NULL, CONSOLE_TEXTMODE_BUFFER, NULL);
WriteConsoleA(tmpbuf, " ", 1, NULL, NULL);
if(SetConsoleActiveScreenBuffer(tmpbuf)==0)
{MessageBoxA(NULL, "ERROR", "ERROR", 0);return;}
bufferdata_ex * dptr;
bufferdata_ex * y_dptr;
int * lcol(new int); //Increases speed by reducing function calls - Experienced about twice as fast drawing!
for(short x=0;x<MAX_X_COORD;x++)
{
y_dptr = _bridge->DATA[x];
for(short y=0;y<MAX_Y_COORD;y++)
{
dptr = (y_dptr+y); //Rewrite to use a constant pointer!
//dptr = &(bridge->DATA[x][y]);
if(dptr->InUse==true)
{
{
pos.X = x;
pos.Y = y;
SetConsoleCursorPosition(output, pos);
//haschanged = false;
}
if(!(*lcol==dptr->color)) //Need for a new color?
{ SetConsoleTextAttribute(output, dptr->color);lcol = &dptr->color;}
char c((char)dptr->sym);
WriteConsoleA(output, &c, 1, NULL, NULL);
lcol = &dptr->color;
}
}
}
SetConsoleTextAttribute(output, bridge->current_color);
SetConsoleCursorPosition(output, last_mouse_position);
SetConsoleActiveScreenBuffer(output);
CloseHandle(tmpbuf);
delete lcol;
}
这个想法对我来说似乎很好，但问题是第一段代码比第二段代码快！所以我的问题是：为什么第一段代码比第二段代码快？
对于不喜欢阅读的人：
为什么第一段代码比另一段快？第一个需要 0.0919 秒才能完成，而第二个需要 0.226 秒。
这也是程序集如何处理指针的副本：
//No pointers
dptr = &(bridge->DATA[x][y]);
001B41C6 mov eax,dword ptr [this]
001B41C9 mov ecx,dword ptr [eax+14h]
001B41CC movsx edx,word ptr [x]
001B41D0 imul edx,edx,370h
001B41D6 lea eax,[ecx+edx+1D4h]
001B41DD movsx ecx,word ptr [y]
001B41E1 shl ecx,4
001B41E4 add eax,ecx
001B41E6 mov dword ptr [dptr],eax
//With pointers
//Pointing to DATA[x]
012C41A5 mov eax,dword ptr [this]
012C41A8 mov ecx,dword ptr [eax+14h]
012C41AB movsx edx,word ptr [x]
012C41AF imul edx,edx,370h
012C41B5 lea eax,[ecx+edx+1D4h]
012C41BC mov dword ptr [y_dptr],eax
//Pointing to DATA[x]+y
012C41E0 movsx eax,word ptr [y]
012C41E4 shl eax,4
012C41E7 add eax,dword ptr [y_dptr]
012C41EA mov dword ptr [dptr],eax
除了这部分代码外，其余部分相同。