在SQL SERVER2005以上版本中，数据页默认开启checksum，标识为m_flagBits & 0x200 == True，其值m_tornBits位于页头0x3C，4字节。
其算法概述如下：

读8KB 进BUF
将BUF头部 CHECKSUM的4字节值清0
uint32 checksum = 0 //初始checksum
for i in range(0,15)://每扇区的初始checksumoverall = 0;for ii in range(0,127)://对当前扇区的每个4字节做累加异或overall = overall ^ BUF[i][ii];//对每扇区的checksum进行移位，方法为向左移位15-i位，//左边移出的15-i位补到最低位。checksum = checksum ^ rol(overall, 15- i);
return checksum; //Gets checksum

c源码如下：

//***CODE***//
#include <stdio.h>
#include <stdlib.h>#define seed 15 //Initial seed(for first sector)
#define CHAR_BIT 8 //***PROTOTYPES***//
unsigned int page_checksum(int page_id, unsigned int *ondisk);
unsigned int rol(unsigned int value, unsigned int rotation);int main(int argc, char *argv[]) {unsigned int computed_checksum; //Var to retrieve calculated checksumunsigned int ondisk_checksum; //Var to retrieve checksum on diskcomputed_checksum = page_checksum(152, &ondisk_checksum); //page_checksum call to retrieve stored and calculated checksum for page 152//***PRINTS***//printf("Calculated checksum: 0x%08x\n", computed_checksum);printf("On disk checksum: 0x%08x\n", ondisk_checksum);}unsigned int page_checksum(int page_id, unsigned int *ondisk)
{FILE *fileptr; unsigned int i; unsigned int j;unsigned int checksum;unsigned int overall;unsigned int *pagebuf[16][128]; //A pointer to describe 2d array [sector][element]fileptr = fopen("C:\\Users\\andre\\Desktop\\teste.mdf", "r+b"); //Open dummy data file for binary readfseek(fileptr, page_id * 8192, SEEK_SET); //Calculate page address on data file and points to itfread(pagebuf, 4, 2048, fileptr); //Read page bufferfclose(fileptr);checksum = 0;overall = 0;*ondisk = pagebuf[0][15]; //This means that torn bits is stored on first sector in 15th element, Internals researches understand thispagebuf[0][15] = 0x00000000; //Fill checksum field with zeroes (this field will be discarded in algorithm)for (i = 0; i < 16; i++) //Loop through sectors{overall = 0; //Reset overall sum for sectorsfor (j = 0; j < 128; j++) //Loop through elements in sector i{overall = overall ^ (unsigned int)pagebuf[i][j]; //XOR operation between sector i elements}checksum = checksum ^ rol(overall, seed - i); //Current checksum is overall for sector i circular shifted by seed (15 - i)}return checksum; //Gets checksum}unsigned int rol(unsigned int value, unsigned int rotation)
{return (value) << (rotation) | (value) >> (sizeof(int) * CHAR_BIT - rotation) & ( (1 << rotation) -1);
}