c++ - 为什么 CRC 和 C++ 代码版本的 CRC 计算不同？

Question

我有一些 C++ 代码，我正在将其移植到 C。当我在 C 代码中计算 CRC 时，出于某种原因，它返回错误的 CRC 值，而 C++ 代码运行良好。我是 C++ 的新手。我需要一些帮助来理解我在返回错误 CRC 值的 C 代码中做错了什么。

我创建了两个单独的文件，一个用于 C，一个用于 C++，试图在两者中实现相同的结果。

/* C++ */

#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

// Calculate crc32 checksum the way CC2538 and CC2650 does it.
int calcCrcLikeChip(const unsigned char *pData, unsigned long ulByteCount)
{
    unsigned long d, ind;
    unsigned long acc = 0xFFFFFFFF;
    const unsigned long ulCrcRand32Lut[] =
    {
        0x00000000, 0x1DB71064, 0x3B6E20C8, 0x26D930AC, 
        0x76DC4190, 0x6B6B51F4, 0x4DB26158, 0x5005713C, 
        0xEDB88320, 0xF00F9344, 0xD6D6A3E8, 0xCB61B38C, 
        0x9B64C2B0, 0x86D3D2D4, 0xA00AE278, 0xBDBDF21C
    };

    while ( ulByteCount-- )
    {
        d = *pData++;
        ind = (acc & 0x0F) ^ (d & 0x0F);
        acc = (acc >> 4) ^ ulCrcRand32Lut[ind];
        ind = (acc & 0x0F) ^ (d >> 4);
        acc = (acc >> 4) ^ ulCrcRand32Lut[ind];
    }

    return (acc ^ 0xFFFFFFFF);
}

std::string fileName;           // File name
int main ()
{
 uint32_t byteCount = 0;            // File size in bytes
 static std::vector<char> pvWrite(1);// Vector to application firmware in.
 static std::ifstream file;     // File stream
 uint32_t fileCrc;
 fileName = "multi_role.bin";
 file.open(fileName.c_str(), std::ios::binary);
 if(file.is_open())
    {
        //
        // Get file size:
        //
        file.seekg(0, std::ios::end);
        byteCount = (uint32_t)file.tellg();
        printf("%u\r\n", byteCount);
        file.seekg(0, std::ios::beg);

        //
        // Read data
        //
        pvWrite.resize(byteCount);
        file.read((char*) &pvWrite[0], byteCount);
    }
    else   
    {
        cout << "Unable to open file " << fileName.c_str();
    }

  fileCrc = calcCrcLikeChip((unsigned char *)&pvWrite[0], byteCount);
  printf("%u\r\n", fileCrc);
}

/* C */

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <stdio.h>

const char *filename = "multi_role.bin";

int calcCrcLikeChip(const unsigned char *pData, unsigned long ulByteCount)
{
    unsigned long d, ind;
    unsigned long acc = 0xFFFFFFFF;
    const unsigned long ulCrcRand32Lut[] =
    {
     0x00000000, 0x1DB71064, 0x3B6E20C8, 0x26D930AC,
     0x76DC4190, 0x6B6B51F4, 0x4DB26158, 0x5005713C,
     0xEDB88320, 0xF00F9344, 0xD6D6A3E8, 0xCB61B38C,
     0x9B64C2B0, 0x86D3D2D4, 0xA00AE278, 0xBDBDF21C
    };

    while (ulByteCount--)
    {
        d = *pData++;
        ind = (acc & 0x0F) ^ (d & 0x0F);
        acc = (acc >> 4) ^ ulCrcRand32Lut[ind];
        ind = (acc & 0x0F) ^ (d >> 4);
        acc = (acc >> 4) ^ ulCrcRand32Lut[ind];
    }

    return (acc ^ 0xFFFFFFFF);
}

/****************************************************************
 * Function Name : openFile
 * Description   : Opens the file
 * Returns       : NULL on failure
 * Params        @file: Path to the file to be opened
 ****************************************************************/
FILE *openFile(const char *file)
{
    FILE *fp = fopen(file, "rb");
    return(fp);
}

/****************************************************************
 * Function Name : getFileSize
 * Description   : Gets the size of the file to be read
 * Returns       : 0 on failure
 * Params        @fp: File descriptor
 ****************************************************************/
long int getFileSize(FILE *fp)
{
    /* Go to end of file */
    if(fseek(fp, 0L, SEEK_END))
        return (0);

    /* Get the size */
    long int sz = ftell(fp);

    /* Put the curser back to 0 */
    if(fseek(fp,0L,SEEK_SET))
        return (0);
    return sz;
}


int main()
{
 static FILE *fPtr = NULL;
 unsigned char *memPtr = NULL;       /* Ptr to hold read data */
 unsigned long fileCrc;
 long fileSz = 0; 

 fPtr = openFile(filename);
 fileSz = getFileSize(fPtr);
 printf("%lu\n", fileSz);
 memPtr = (unsigned char*)calloc(fileSz, sizeof(unsigned char));
 fread((char*)memPtr,1 , fileSz, fPtr);
 fileCrc = calcCrcLikeChip((const unsigned char*)memPtr, fileSz);
 printf("fileCrc: %lu\n", fileCrc);
}

CRC 的预期结果 = 2637331102(适用于 C++)C中的错误结果=18446744072051915422

Answer 1

这几乎肯定是 32 位与 64 位编译器的问题。或者至少 sizeof(long)两种编译器模式之间似乎有所不同。

证明:

C++:              2637331102 == ‭         9D327A9E
C  :    18446744072051915422 == FFFFFFFF 9D327A9E

请注意，“C”结果的后半部分确实与 C++ 结果匹配。只是“C”结果是一个 64 位数字。据推测，9D327A9E 已从 32 位值符号扩展为 64 位有符号值。

将两个实现中的所有这些声明显式更改为 32 位:

来自这里:

unsigned long d, ind;
unsigned long acc = 0xFFFFFFFF;
const unsigned long ulCrcRand32Lut[] =

对此:

uint32_t d, ind;
uint32_t acc = 0xFFFFFFFF;
const uint32_t ulCrcRand32Lut[] =

您可以 #include <stdint.h>得到uint32_t类型。

按照下面评论中的建议，将函数的返回类型更改为 uint32_t以及。更好:

uint32_t calcCrcLikeChip(const unsigned char *pData, unsigned long ulByteCount)
{
    uint32_t d, ind;
    uint32_t acc = 0xFFFFFFFF;
    const uint32_t ulCrcRand32Lut[] =
    {
        0x00000000, 0x1DB71064, 0x3B6E20C8, 0x26D930AC, 
        0x76DC4190, 0x6B6B51F4, 0x4DB26158, 0x5005713C, 
        0xEDB88320, 0xF00F9344, 0xD6D6A3E8, 0xCB61B38C, 
        0x9B64C2B0, 0x86D3D2D4, 0xA00AE278, 0xBDBDF21C
    };

    while ( ulByteCount > 0 )
    {
        ulByteCount--;
        d = *pData++;
        ind = (acc & 0x0F) ^ (d & 0x0F);
        acc = (acc >> 4) ^ ulCrcRand32Lut[ind];
        ind = (acc & 0x0F) ^ (d >> 4);
        acc = (acc >> 4) ^ ulCrcRand32Lut[ind];
    }

    return (acc ^ 0xFFFFFFFF);
}