ISDIGIT算法问题：两次比较与表查找比较谁更快

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;//4056026MSVCR100.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;

}