crc16.c

这是一个冗余校验的程序

包含三种方法的计算 CRC16 校验（查表、计算、查表＋计算）- -
                                       


附件 RTX51中容易混淆的几个问题.doc：http://blog.blogchina.com/upload/2004-11-17/200411170906168061.doc/////////////////////////////////////////////////////
//文件: crc.c                                      //
//功能: 计算 CRC16 校验                            //
//作者: 邵子扬 [e-mail]                  //
//时间: 2004-Fer-26                                //
//版本: 1.0                                        //
//说明: 这是针对PIC的版本，对于Keil51需要将下面数组//
//      中的const换成code                          //
//-------------------------------------------------//
//修改:                                            //
//  版本: 1.2                                      //
//  作者:邵子扬                                    //
//  时间:2004-Oct-12                               //
//  原因:程序优化，计算花费的时间更短。经过模拟仿真//
//       ，计算100个数据的速度提高27%              //
//-------------------------------------------------//
//  版本: 1.4                                      //
//  作者:邵子扬                                    //
//  时间:2004-Oct-20                               //
//  原因:将三种计算方法合在一个文件中，根据实际需要//
//       选择，用宏定义区分，默认查表法            //
//       Method_Calc         计算法                //
//       Method_TableCalc    计算＋查表            //
//       Method_Table        查表                  //
//           __      __                            //
//  by      (  / _   _/ '(__/_   _                 //
//  2004   __)/)(/()/__/  / (//)(/  @126.com       //
//                             _/                  //
/////////////////////////////////////////////////////

//#define Method_Calc
//#define Method_TableCalc

#if !defined(Method_Table) && \
    !defined(Method_Calc) && \
    !defined(Method_TableCalc)
#define Method_Table
#endif

void crc16(unsigned char *buf,unsigned char n,unsigned char *h,unsigned char *l);

#if defined(Method_Table)
//查表
const unsigned char crctableh[256]={
  0x00, 0x10, 0x20, 0x30, 0x40, 0x50, 0x60, 0x70,
  0x81, 0x91, 0xA1, 0xB1, 0xC1, 0xD1, 0xE1, 0xF1,
  0x12, 0x02, 0x32, 0x22, 0x52, 0x42, 0x72, 0x62,
  0x93, 0x83, 0xB3, 0xA3, 0xD3, 0xC3, 0xF3, 0xE3,
  0x24, 0x34, 0x04, 0x14, 0x64, 0x74, 0x44, 0x54,
  0xA5, 0xB5, 0x85, 0x95, 0xE5, 0xF5, 0xC5, 0xD5,
  0x36, 0x26, 0x16, 0x06, 0x76, 0x66, 0x56, 0x46,
  0xB7, 0xA7, 0x97, 0x87, 0xF7, 0xE7, 0xD7, 0xC7,
  0x48, 0x58, 0x68, 0x78, 0x08, 0x18, 0x28, 0x38,
  0xC9, 0xD9, 0xE9, 0xF9, 0x89, 0x99, 0xA9, 0xB9,
  0x5A, 0x4A, 0x7A, 0x6A, 0x1A, 0x0A, 0x3A, 0x2A,
  0xDB, 0xCB, 0xFB, 0xEB, 0x9B, 0x8B, 0xBB, 0xAB,
  0x6C, 0x7C, 0x4C, 0x5C, 0x2C, 0x3C, 0x0C, 0x1C,
  0xED, 0xFD, 0xCD, 0xDD, 0xAD, 0xBD, 0x8D, 0x9D,
  0x7E, 0x6E, 0x5E, 0x4E, 0x3E, 0x2E, 0x1E, 0x0E,
  0xFF, 0xEF, 0xDF, 0xCF, 0xBF, 0xAF, 0x9F, 0x8F,
  0x91, 0x81, 0xB1, 0xA1, 0xD1, 0xC1, 0xF1, 0xE1,
  0x10, 0x00, 0x30, 0x20, 0x50, 0x40, 0x70, 0x60,
  0x83, 0x93, 0xA3, 0xB3, 0xC3, 0xD3, 0xE3, 0xF3,
  0x02, 0x12, 0x22, 0x32, 0x42, 0x52, 0x62, 0x72,
  0xB5, 0xA5, 0x95, 0x85, 0xF5, 0xE5, 0xD5, 0xC5,
  0x34, 0x24, 0x14, 0x04, 0x74, 0x64, 0x54, 0x44,
  0xA7, 0xB7, 0x87, 0x97, 0xE7, 0xF7, 0xC7, 0xD7,
  0x26, 0x36, 0x06, 0x16, 0x66, 0x76, 0x46, 0x56,
  0xD9, 0xC9, 0xF9, 0xE9, 0x99, 0x89, 0xB9, 0xA9,
  0x58, 0x48, 0x78, 0x68, 0x18, 0x08, 0x38, 0x28,
  0xCB, 0xDB, 0xEB, 0xFB, 0x8B, 0x9B, 0xAB, 0xBB,
  0x4A, 0x5A, 0x6A, 0x7A, 0x0A, 0x1A, 0x2A, 0x3A,
  0xFD, 0xED, 0xDD, 0xCD, 0xBD, 0xAD, 0x9D, 0x8D,
  0x7C, 0x6C, 0x5C, 0x4C, 0x3C, 0x2C, 0x1C, 0x0C,
  0xEF, 0xFF, 0xCF, 0xDF, 0xAF, 0xBF, 0x8F, 0x9F,
  0x6E, 0x7E, 0x4E, 0x5E, 0x2E, 0x3E, 0x0E, 0x1E,
};
const unsigned char crctablel[256]={
  0x00, 0x21, 0x42, 0x63, 0x84, 0xA5, 0xC6, 0xE7,
  0x08, 0x29, 0x4A, 0x6B, 0x8C, 0xAD, 0xCE, 0xEF,
  0x31, 0x10, 0x73, 0x52, 0xB5, 0x94, 0xF7, 0xD6,
  0x39, 0x18, 0x7B, 0x5A, 0xBD, 0x9C, 0xFF, 0xDE,
  0x62, 0x43, 0x20, 0x01, 0xE6, 0xC7, 0xA4, 0x85,
  0x6A, 0x4B, 0x28, 0x09, 0xEE, 0xCF, 0xAC, 0x8D,
  0x53, 0x72, 0x11, 0x30, 0xD7, 0xF6, 0x95, 0xB4,
  0x5B, 0x7A, 0x19, 0x38, 0xDF, 0xFE, 0x9D, 0xBC,
  0xC4, 0xE5, 0x86, 0xA7, 0x40, 0x61, 0x02, 0x23,
  0xCC, 0xED, 0x8E, 0xAF, 0x48, 0x69, 0x0A, 0x2B,
  0xF5, 0xD4, 0xB7, 0x96, 0x71, 0x50, 0x33, 0x12,
  0xFD, 0xDC, 0xBF, 0x9E, 0x79, 0x58, 0x3B, 0x1A,
  0xA6, 0x87, 0xE4, 0xC5, 0x22, 0x03, 0x60, 0x41,
  0xAE, 0x8F, 0xEC, 0xCD, 0x2A, 0x0B, 0x68, 0x49,
  0x97, 0xB6, 0xD5, 0xF4, 0x13, 0x32, 0x51, 0x70,
  0x9F, 0xBE, 0xDD, 0xFC, 0x1B, 0x3A, 0x59, 0x78,
  0x88, 0xA9, 0xCA, 0xEB, 0x0C, 0x2D, 0x4E, 0x6F,
  0x80, 0xA1, 0xC2, 0xE3, 0x04, 0x25, 0x46, 0x67,
  0xB9, 0x98, 0xFB, 0xDA, 0x3D, 0x1C, 0x7F, 0x5E,
  0xB1, 0x90, 0xF3, 0xD2, 0x35, 0x14, 0x77, 0x56,
  0xEA, 0xCB, 0xA8, 0x89, 0x6E, 0x4F, 0x2C, 0x0D,
  0xE2, 0xC3, 0xA0, 0x81, 0x66, 0x47, 0x24, 0x05,
  0xDB, 0xFA, 0x99, 0xB8, 0x5F, 0x7E, 0x1D, 0x3C,
  0xD3, 0xF2, 0x91, 0xB0, 0x57, 0x76, 0x15, 0x34,
  0x4C, 0x6D, 0x0E, 0x2F, 0xC8, 0xE9, 0x8A, 0xAB,
  0x44, 0x65, 0x06, 0x27, 0xC0, 0xE1, 0x82, 0xA3,
  0x7D, 0x5C, 0x3F, 0x1E, 0xF9, 0xD8, 0xBB, 0x9A,
  0x75, 0x54, 0x37, 0x16, 0xF1, 0xD0, 0xB3, 0x92,
  0x2E, 0x0F, 0x6C, 0x4D, 0xAA, 0x8B, 0xE8, 0xC9,
  0x26, 0x07, 0x64, 0x45, 0xA2, 0x83, 0xE0, 0xC1,
  0x1F, 0x3E, 0x5D, 0x7C, 0x9B, 0xBA, 0xD9, 0xF8,
  0x17, 0x36, 0x55, 0x74, 0x93, 0xB2, 0xD1, 0xF0,
};

void crc16(unsigned char *buf,unsigned char n,unsigned char *h,unsigned char *l)
{
 unsigned char i,t,a,b;

 a = b = 0;
/* while(n != 0)
 {
  t = a ^ *buf;
  a = b ^ crctableh[t];
  b = crctablel[t];
  n --;
  buf ++;
 }*/
 for(i=0;i {
  t = a ^ buf[i];
  a = b ^ crctableh[t];
  b = crctablel[t];   
 }
 *h = a;
 *l = b;
}
#elif defined(Method_Calc)
//计算
void crc16(unsigned char *buf,unsigned char n,unsigned char *h,unsigned char *l)
{
 unsigned char i,t;
 union
 {
  unsigned char c[2];
  unsigned int x;
 }crc;

 crc.x = 0;
 while(n > 0)
 {
  crc.c[0] ^= *buf;
  for(i = 8;i > 0;i --)
  {
   t = crc.c[0];
   crc.x <<= 1;
   if( t & 0x80)crc.x ^= 0x1021;
  }
  buf ++;
  n --;
 }
 *h = crc.c[0];
 *l = crc.c[1];
}
#elif defined(Method_TableCalc)
//查表＋计算
void crc16(unsigned char *buf,unsigned char n,unsigned char *h,unsigned char *l)
{
 unsigned char t;
 const unsigned int crch[16]=  // CRC余式表
 {
  0x00,0x10,0x20,0x30,0x40,0x50,0x60,0x70,
  0x81,0x91,0xa1,0xb1,0xc1,0xd1,0xe1,0xf1,
 };
 const unsigned int crcl[16]=  // CRC余式表
 {
  0x00,0x21,0x42,0x63,0x84,0xa5,0xc6,0xe7,
  0x08,0x29,0x4a,0x6b,0x8c,0xad,0xce,0xef,
 };
 union
 {
  unsigned char c[2];
  unsigned int x;
 }crc;

 crc.x=0;
 while( n -- != 0)
 {
  t = (crc.c[0] / 16) ^ (*buf / 16);
  crc.x <<= 4;
  crc.c[0] ^= crch[t];
  crc.c[1] ^= crcl[t];
  t = (crc.c[0] / 16) ^ (*buf % 16);
  crc.x <<= 4;
  crc.c[0] ^= crch[t];
  crc.c[1] ^= crcl[t];
  buf ++;
 }
 *h = crc.c[0];
 *l = crc.c[1];
}
#endif