CRC32 几个参数 附带源码
作者：互联网
标准 CRC32 参数如下：
非标准 CRC32:
多项式的值：0x04C11DB7 ,
初始值：0xFFFFFFFF，
结果异或值： 0x0，
数据输入反转 关闭，
数据输出反转 关闭。
源码是非标准CRC32, 可以更改里面的参数 变成 标准 CRC32;
/**********************************************************************
*
* Filename: crc32.c
*
* Description: Slow and fast implementations of the CRC32 standards.
*
* Notes: The parameters for each supported CRC standard are
* defined in the header file crc.h. The implementations
* here should stand up to further additions to that list.
*
*
* Copyright (c) 2000 by Michael Barr. This software is placed into
* the public domain and may be used for any purpose. However, this
* notice must not be changed or removed and no warranty is either
* expressed or implied by its publication or distribution.
**********************************************************************/
/**
* @file crc32.c
* @brief Implementation of crc32.h
*/
#include "crc32.h"
#define FALSE 0
#define TRUE !FALSE
typedef unsigned long crc;
#define CRC_NAME "CRC-32"
// 多项式
#define POLYNOMIAL 0x04C11DB7
//#define POLYNOMIAL 0xEDB88320
//#define POLYNOMIAL 0xDB710641
//#define POLYNOMIAL 0x82608ED8
// 初始值
#define INITIAL_REMAINDER 0xFFFFFFFF
// 结果异或值
#define FINAL_XOR_VALUE 0x0UL
// 输入反转 关闭
#define REFLECT_DATA FALSE
// 输出反转 关闭
#define REFLECT_REMAINDER FALSE
/*
* Derive parameters from the standard-specific parameters in crc32.h.
*/
#define WIDTH (8 * sizeof(crc))
#define TOPBIT (1U << (WIDTH - 1))
#if (REFLECT_DATA == TRUE)
#undef REFLECT_DATA
#define REFLECT_DATA(X) ((unsigned char) reflect((X), 8))
#else
#undef REFLECT_DATA
#define REFLECT_DATA(X) (X)
#endif
#if (REFLECT_REMAINDER == TRUE)
#undef REFLECT_REMAINDER
#define REFLECT_REMAINDER(X) ((crc) reflect((X), WIDTH))
#else
#undef REFLECT_REMAINDER
#define REFLECT_REMAINDER(X) (X)
#endif
/*********************************************************************
*
* Function: reflect()
*
* Description: Reorder the bits of a binary sequence, by reflecting
* them about the middle position.
*
* Notes: No checking is done that nBits <= 32.
*
* Returns: The reflection of the original data.
*
*********************************************************************/
static unsigned long
reflect(unsigned long data, unsigned char nBits)
{
unsigned long reflection = 0x00000000;
unsigned char bit;
/*
* Reflect the data about the center bit.
*/
for (bit = 0; bit < nBits; ++bit) {
/*
* If the LSB bit is set, set the reflection of it.
*/
if (data & 0x01) {
reflection |= (1 << ((nBits - 1) - bit));
}
data = (data >> 1);
}
return (reflection);
} /* reflect() */
/*********************************************************************
*
* Function: crc32()
*
* Description: Compute the CRC of a given message.
*
* Notes:
*
* Returns: The CRC of the message.
*
*********************************************************************/
uint32_t crc32(const void *data, int nBytes)
{
crc remainder = INITIAL_REMAINDER;
int byte;
unsigned char bit;
unsigned char const *message = data;
/*
* Perform modulo-2 division, a byte at a time.
*/
for (byte = 0; byte < nBytes; ++byte) {
/*
* Bring the next byte into the remainder.
*/
remainder ^= (REFLECT_DATA(message[byte]) << (WIDTH - 8));
/*
* Perform modulo-2 division, a bit at a time.
*/
for (bit = 8; bit > 0; --bit) {
/*
* Try to divide the current data bit.
*/
if (remainder & TOPBIT) {
remainder = (remainder << 1) ^ POLYNOMIAL;
} else {
remainder = (remainder << 1);
}
}
}
/*
* The final remainder is the CRC result.
*/
return (REFLECT_REMAINDER(remainder) ^ FINAL_XOR_VALUE);
} /* crc32() */
/*********************************************************************
*
* Function: crc32_continue()
*
* Description: Compute the CRC of a given message.
*
* Notes:
*
* Returns: The CRC of the message.
*
*********************************************************************/
uint32_t crc32_continue(uint32_t prev_crc, const void *data, int nBytes)
{
crc remainder = REFLECT_REMAINDER(prev_crc ^ FINAL_XOR_VALUE);
int byte;
unsigned char bit;
unsigned char const *message = data;
/*
* Perform modulo-2 division, a byte at a time.
*/
for (byte = 0; byte < nBytes; ++byte) {
/*
* Bring the next byte into the remainder.
*/
remainder ^= (REFLECT_DATA(message[byte]) << (WIDTH - 8));
/*
* Perform modulo-2 division, a bit at a time.
*/
for (bit = 8; bit > 0; --bit) {
/*
* Try to divide the current data bit.
*/
if (remainder & TOPBIT) {
remainder = (remainder << 1) ^ POLYNOMIAL;
} else {
remainder = (remainder << 1);
}
}
}
/*
* The final remainder is the CRC result.
*/
return (REFLECT_REMAINDER(remainder) ^ FINAL_XOR_VALUE);
} /* crc32_continue() */
/**************************************************************************************************
* @fn crc16
*
* @brief Run the CRC16 Polynomial calculation over the byte parameter.
*
* input parameters
*
* @param crc - Running CRC calculated so far.
* @param val - Value on which to run the CRC16.
*
* output parameters
*
* None.
*
* @return crc - Updated for the run.
**************************************************************************************************
*/
uint16_t crc16(uint16_t crc, uint8_t val)
{
const uint16_t poly = 0x1021;
uint8_t cnt;
for (cnt = 0; cnt < 8; cnt++, val <<= 1)
{
uint8_t msb = (crc & 0x8000) ? 1 : 0;
crc <<= 1;
if (val & 0x80) crc |= 0x0001;
if (msb) crc ^= poly;
}
return crc;
}
/**********************************************************************
*
* Filename: crc.h
*
* Description: A header file describing the various CRC standards.
*
* Notes:
*
*
* Copyright (c) 2000 by Michael Barr. This software is placed into
* the public domain and may be used for any purpose. However, this
* notice must not be changed or removed and no warranty is either
* expressed or implied by its publication or distribution.
**********************************************************************/
/**
* @file crc.h
* @brief CRC functions
*/
#ifndef _crc_h
#define _crc_h
#include "stdint.h"
#ifdef __cplusplus
extern "C" {
#endif
uint32_t crc32(const void *data, int nBytes);
uint32_t crc32_continue(uint32_t prev_crc, const void *data, int nBytes);
uint16_t crc16(uint16_t crc, uint8_t val);
#ifdef __cplusplus
}
#endif
#endif
标签：CRC,附带,remainder,crc,源码,CRC32,byte,crc32,define 来源： https://www.cnblogs.com/suozhang/p/15789208.html