(简单问题)ISDIGIT算法问题：两次比较与取地址表查找比较谁更快

[GKatHere]

在《C++实践之路》[美]Barotsz Milewski书3.5.5中说，表查找比两次比较更快，实测不然，表查找略为更慢一些??

#define ISDIGIT2(c) ( ((c) >= '0') )   		// 124800
#define ISDIGIT(c) ( ((c) >= '0') && ((c) <= '9') )	//1404000
if (bDig[UCHAR(n)]) isd+=2;     		//1560010 表查找
if (isdigit(UCHAR(n))) isd+=2;    		//4056026 MSVCR100.isdigit

全例如下：

int _tmain(int argc, _TCHAR* argv[])
{
	srand(::GetTickCount());
BOOL bDig[0xff] ={0};

	WCHAR szw[MAX_PATH];
	CHAR sza[MAX_PATH];


	 

	FILETIME lpCreationTime,  lpExitTime,   lpKernelTime, lpUserTime;
	FILETIME lpCreationTime2,  lpExitTime2,   lpKernelTime2, lpUserTime2;
	int isd=0;

	::GetThreadTimes(::GetCurrentThread(), &lpCreationTime,  &lpExitTime,   &lpKernelTime, &lpUserTime);
	isd=0;
#define ISDIGIT2(c) ( ((c) >= '0') )			//	124800
	for (ULONG_PTR n=0; n <0x3ffffff; n++)
	{
		if (ISDIGIT2(UCHAR(n))) isd+=2;
	}
	::GetThreadTimes(::GetCurrentThread(), &lpCreationTime2,  &lpExitTime2,   &lpKernelTime2, &lpUserTime2);
	swprintf(szw, __FUNCTIONW__ L" %d,\t%d, \n", isd, 
		lpKernelTime2.dwLowDateTime -lpKernelTime.dwLowDateTime + 
		(lpUserTime2.dwLowDateTime -lpUserTime.dwLowDateTime )
		);
	wprintf(szw);

	::GetThreadTimes(::GetCurrentThread(), &lpCreationTime,  &lpExitTime,   &lpKernelTime, &lpUserTime);
	isd=0;
#define ISDIGIT(c) ( ((c) >= '0') && ((c) <= '9') )//1404000	
	for (ULONG_PTR n=0; n <0x3ffffff; n++)
	{
		if (ISDIGIT(UCHAR(n))) isd+=2;
	}
	::GetThreadTimes(::GetCurrentThread(), &lpCreationTime2,  &lpExitTime2,   &lpKernelTime2, &lpUserTime2);
	swprintf(szw, __FUNCTIONW__ L" %d,\t%d, \n", isd, 
		lpKernelTime2.dwLowDateTime -lpKernelTime.dwLowDateTime + 
		(lpUserTime2.dwLowDateTime -lpUserTime.dwLowDateTime )
		);
	wprintf(szw);


	::GetThreadTimes(::GetCurrentThread(), &lpCreationTime,  &lpExitTime,   &lpKernelTime, &lpUserTime);
	isd=0;
	for (ULONG_PTR n=0; n <0x3ffffff; n++)
		if (bDig[UCHAR(n)]) isd+=2;					//1560010
	::GetThreadTimes(::GetCurrentThread(), &lpCreationTime2,  &lpExitTime2,   &lpKernelTime2, &lpUserTime2);
	swprintf(szw, __FUNCTIONW__ L" %d,\t%d, \n",  isd, 
		lpKernelTime2.dwLowDateTime -lpKernelTime.dwLowDateTime + 
		(lpUserTime2.dwLowDateTime -lpUserTime.dwLowDateTime )
		);
	wprintf(szw);

	::GetThreadTimes(::GetCurrentThread(), &lpCreationTime,  &lpExitTime,   &lpKernelTime, &lpUserTime);
	isd=0;
	for (ULONG_PTR n=0; n <0x3ffffff; n++)
		if (isdigit(UCHAR(n))) isd+=2;				//4056026	MSVCR100.isdigit 
	::GetThreadTimes(::GetCurrentThread(), &lpCreationTime2,  &lpExitTime2,   &lpKernelTime2, &lpUserTime2);
	swprintf(szw, __FUNCTIONW__ L" %d,\t%d, \n", isd, 
		lpKernelTime2.dwLowDateTime -lpKernelTime.dwLowDateTime + 
		(lpUserTime2.dwLowDateTime -lpUserTime.dwLowDateTime )
		);
	wprintf(szw);


	getchar();
	return 0;}