CRC 16程序來計算校驗和

我目前正在寫一個CRC16程序，它使用CRC 16多項式計算CRC字符X^16 + X^15 + X^2 + 1。程序應該從標準輸入讀取數據，並以十六進制輸出16位CRC。儘管如此，當我執行程序時，我得到了錯誤的輸出值。CRC 16程序來計算校驗和

這裏是我的代碼：

#include <stdint.h> 

#define CRC16 0x8005 

unsigned short crc(unsigned char msg[], int len) 
{ 
    unsigned short out = 0; 
    int bits = 0, t_flag; 
    int x = 0; 

    /* Sanity check: */ 
    if(msg == NULL) 
     return 0; 

    while(len > x) 
    { 
     unsigned short data = msg[x]; 
     t_flag = out >> 15; 

     /* Get next bit: */ 
     out <<= 1; 
     out |= (data >> bits) & 1; // item a) work from the least significant bits 

     /* Increment bit counter: */ 
     bits++; 
     if(bits > 7) 
     { 
      bits = 0; 
      data++; 
      len--; 
     } 

     /* Cycle check: */ 
     if(t_flag) 
      out ^= CRC16; 

    } 

    // item b) "push out" the last 16 bits 
    int i; 
    for (i = 0; i < 16; ++i) { 
     t_flag = out >> 15; 
     out <<= 1; 
     if(t_flag) 
      out ^= CRC16; 
    } 

    // item c) reverse the bits 
    unsigned short crc1 = 0; 
    i = 0x8000; 
    int j = 0x0001; 
    for (; i != 0; i >>=1, j <<= 1) { 
     if (i & out) crc1 |= j; 
    } 

    return crc1; 
} 
int main (int argc, char *argv[]) { 
//if (argv[1] == "trace") { 

//printf(argv[1]); 
//} 
char ARGV; 


if(argc < 1) { 

    printf("Must have atleast one arguments\n"); 
     return 1; 

} 
char buf[256]; 
int c , r; 
int count = -1; 

while((c = getchar())!=EOF) { 
    buf[count++] = putchar(c); 
} 

r = crc(buf, count); 

//printf("%s\n",argv[1]); 

printf("%04hx\n", r); 
//print("%x\n", argv[1]); 
return (0); 
//printf(" %4x\n", crc(argv[1], 16)); 

}

輸出：

（我讀123456789我的txt文件）

./crc1 < testfile.txt 
123456789 
7bda

它應該是BB3D，但我得到7bda。有人能幫我弄清楚我做錯了什麼嗎？

來源

2014-02-21 zer0

在'的buf [計數++] =的putchar（C）'，第一個字節是在'BUF [-1] ' –

測試'if（argc <1）'是無用的，因爲在所有（託管）系統中，'argc'至少是'1'。 –

所以我應該從0開始buf – zer0

#include<stdio.h> 
#include<stdint.h> 

#define CRC16 0x8005 

uint16_t gen_crc16(const uint8_t *data, uint16_t size) 
{ 
    uint16_t out = 0; 
    int bits_read = 0, bit_flag; 


    // test 
    printf("buffer in function %s\n", data); 

    /* Sanity check: */ 
    if(data == NULL) 
     return 0; 

    while(size > 0) 
    { 
     bit_flag = out >> 15; 

     /* Get next bit: */ 
     out <<= 1; 
     out |= (*data >> bits_read) & 1; // item a) work from the least significant bits 

     /* Increment bit counter: */ 
     bits_read++; 
     if(bits_read > 7) 
     { 
      bits_read = 0; 
      data++; 
      size--; 
     } 

     /* Cycle check: */ 
     if(bit_flag) 
      out ^= CRC16; 

    } 

    // item b) "push out" the last 16 bits 
    int i; 
    for (i = 0; i < 16; ++i) { 
     bit_flag = out >> 15; 
     out <<= 1; 
     if(bit_flag) 
      out ^= CRC16; 
    } 

    // item c) reverse the bits 
    uint16_t crc = 0; 
    i = 0x8000; 
    int j = 0x0001; 
    for (; i != 0; i >>=1, j <<= 1) { 
     if (i & out) crc |= j; 
    } 

    return crc; 
} 

int main() 
{ 
    char buf[]="123456789"; 
    int c , r; 
    printf ("the buf has %s", buf); 
    r = gen_crc16(buf,sizeof(buf)-1); 
    printf("%04hx\n", r); 

    return (0); 
}

來源

2015-05-06 09:34:54 manjunath

太棒了，我建議使用size_t而不是uint16_t作爲size參數。 – Maghis

mmmmm，爲什麼不嘗試先使用一些已經實現的實現？是你的多項式正確嗎？ X^16 + X^2 + X^0？也許是X^16 + X^15 + X^2 + X^0

uint16_t Crc16WordCalc(const uint16_t *DataIn, uint32_t DataLen, uint16_t InitVal) 
{ 
    uint32_t i; 
    uint16_t CRCSum; 
    uint8_t tempData; 

    CRCSum = InitVal; 
    for(i = 0; i < DataLen; i++) 
    { 
     tempData = (uint8_t)((DataIn[i] >> 8) & 0xFF); 
     CRCSum = (CRCSum<<8)^CRC16Lut[((CRCSum>>8)&0xFF)^tempData]; 

     tempData = (uint8_t)(DataIn[i] & 0xFF); 
     CRCSum = (CRCSum<<8)^CRC16Lut[((CRCSum>>8)&0xFF)^tempData]; 
    } 

    return CRCSum; 
} 


// LOOK UP TABLE for CRC16 generation 
// Polynomial X^16+X^15+X^2+1 
0x0000, 0x8005, 0x800F, 0x000A, 0x801B, 0x001E, 0x0014, 0x8011, 
0x8033, 0x0036, 0x003C, 0x8039, 0x0028, 0x802D, 0x8027, 0x0022, 
0x8063, 0x0066, 0x006C, 0x8069, 0x0078, 0x807D, 0x8077, 0x0072, 
0x0050, 0x8055, 0x805F, 0x005A, 0x804B, 0x004E, 0x0044, 0x8041, 
0x80C3, 0x00C6, 0x00CC, 0x80C9, 0x00D8, 0x80DD, 0x80D7, 0x00D2, 
0x00F0, 0x80F5, 0x80FF, 0x00FA, 0x80EB, 0x00EE, 0x00E4, 0x80E1, 
0x00A0, 0x80A5, 0x80AF, 0x00AA, 0x80BB, 0x00BE, 0x00B4, 0x80B1, 
0x8093, 0x0096, 0x009C, 0x8099, 0x0088, 0x808D, 0x8087, 0x0082, 
0x8183, 0x0186, 0x018C, 0x8189, 0x0198, 0x819D, 0x8197, 0x0192, 
0x01B0, 0x81B5, 0x81BF, 0x01BA, 0x81AB, 0x01AE, 0x01A4, 0x81A1, 
0x01E0, 0x81E5, 0x81EF, 0x01EA, 0x81FB, 0x01FE, 0x01F4, 0x81F1, 
0x81D3, 0x01D6, 0x01DC, 0x81D9, 0x01C8, 0x81CD, 0x81C7, 0x01C2, 
0x0140, 0x8145, 0x814F, 0x014A, 0x815B, 0x015E, 0x0154, 0x8151, 
0x8173, 0x0176, 0x017C, 0x8179, 0x0168, 0x816D, 0x8167, 0x0162, 
0x8123, 0x0126, 0x012C, 0x8129, 0x0138, 0x813D, 0x8137, 0x0132, 
0x0110, 0x8115, 0x811F, 0x011A, 0x810B, 0x010E, 0x0104, 0x8101, 
0x8303, 0x0306, 0x030C, 0x8309, 0x0318, 0x831D, 0x8317, 0x0312, 
0x0330, 0x8335, 0x833F, 0x033A, 0x832B, 0x032E, 0x0324, 0x8321, 
0x0360, 0x8365, 0x836F, 0x036A, 0x837B, 0x037E, 0x0374, 0x8371, 
0x8353, 0x0356, 0x035C, 0x8359, 0x0348, 0x834D, 0x8347, 0x0342, 
0x03C0, 0x83C5, 0x83CF, 0x03CA, 0x83DB, 0x03DE, 0x03D4, 0x83D1, 
0x83F3, 0x03F6, 0x03FC, 0x83F9, 0x03E8, 0x83ED, 0x83E7, 0x03E2, 
0x83A3, 0x03A6, 0x03AC, 0x83A9, 0x03B8, 0x83BD, 0x83B7, 0x03B2, 
0x0390, 0x8395, 0x839F, 0x039A, 0x838B, 0x038E, 0x0384, 0x8381, 
0x0280, 0x8285, 0x828F, 0x028A, 0x829B, 0x029E, 0x0294, 0x8291, 
0x82B3, 0x02B6, 0x02BC, 0x82B9, 0x02A8, 0x82AD, 0x82A7, 0x02A2, 
0x82E3, 0x02E6, 0x02EC, 0x82E9, 0x02F8, 0x82FD, 0x82F7, 0x02F2, 
0x02D0, 0x82D5, 0x82DF, 0x02DA, 0x82CB, 0x02CE, 0x02C4, 0x82C1, 
0x8243, 0x0246, 0x024C, 0x8249, 0x0258, 0x825D, 0x8257, 0x0252, 
0x0270, 0x8275, 0x827F, 0x027A, 0x826B, 0x026E, 0x0264, 0x8261, 
0x0220, 0x8225, 0x822F, 0x022A, 0x823B, 0x023E, 0x0234, 0x8231, 
0x8213, 0x0216, 0x021C, 0x8219, 0x0208, 0x820D, 0x8207, 0x0202

來源

2014-02-21 16:18:16

是的對不起，我打算把X^16 + X^15 + X^2 + X^0，但對於我的類項目，它必須使用unsigned short crc（unsigned char msg []，int len）並且沒有查找表 – zer0

CRC 16程序來計算校驗和

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