109 lines
3.3 KiB
C
109 lines
3.3 KiB
C
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#include "hamming.h"
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/**
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* @brief 计算一个字节中1的个数
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* @param byte 输入字节
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* @return 返回字节中1的个数
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*/
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static inline int countOnes(unsigned char byte) {
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static const unsigned char ones[16] = {0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4};
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return ones[byte & 0x0F] + ones[byte >> 4];
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}
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/**
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* @brief 计算汉明码的校验位
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* @param data 输入数据数组
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* @param size 数据大小
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* @param parity 输出的校验位数组（3字节）
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* @note 校验位计算包括：
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* - 对每个数据位进行异或运算生成校验位
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* - 最后一个校验字节的最高位用于总体奇偶校验
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*/
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void calculateParity(const unsigned char *data, int size, unsigned char *parity) {
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// 初始化校验位数组
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memset(parity, 0, PARITY_BYTES);
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int totalOnes = 0;
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// 对每个数据字节
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for(int i = 0; i < size; i++) {
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unsigned char byte = data[i];
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totalOnes += countOnes(byte);
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// 对字节中的每一位
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for(int j = 0; j < 8; j++) {
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if(byte & (1 << j)) {
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// 计算该位在整个数据中的位置
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int bitPos = i * 8 + j;
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// 更新相应的校验位
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for(int k = 0; k < 20; k++) {
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if(bitPos & (1 << k)) {
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if(k < 8)
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parity[0] ^= (1 << k);
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else if(k < 16)
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parity[1] ^= (1 << (k - 8));
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else
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parity[2] ^= (1 << (k - 16));
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}
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}
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}
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}
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}
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// 添加总体奇偶校验
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if(totalOnes % 2) {
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parity[2] |= 0x08; // 设置最高位
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}
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}
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/**
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* @brief 检测并纠正数据中的错误
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* @param data 需要检查的数据
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* @param size 数据大小
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* @param parity 原始校验位
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* @return 返回检测结果：
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* 0 - 无错误
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* 1 - 检测到并纠正了单比特错误
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* -1 - 校验位错误
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* -2 - 检测到多位错误
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*/
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int detectAndCorrect(unsigned char *data, int size, const unsigned char *parity) {
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unsigned char currentParity[PARITY_BYTES];
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calculateParity(data, size, currentParity);
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// printf("parity: %02X %02X %02X\n", parity[2], parity[1], parity[0]);
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// printf("currentParity: %02X %02X %02X\n", currentParity[2], currentParity[1], currentParity[0]);
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// 计算syndrome
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unsigned int syndrome = 0;
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syndrome |= (currentParity[0] ^ parity[0]);
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syndrome |= (currentParity[1] ^ parity[1]) << 8;
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syndrome |= ((currentParity[2] ^ parity[2]) & 0x07) << 16;
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// 检查总体奇偶校验
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int parityError = ((currentParity[2] ^ parity[2]) & 0x08) ? 1 : 0;
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if(syndrome == 0) {
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if(parityError) {
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return -2; // 检测到多位错误
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}
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return 0; // 无错误
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}
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if(!parityError) {
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return -1; // 校验位错误（syndrome不为0但奇偶校验正确）
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}
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// 单比特错误
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int bitPos = syndrome;
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int bytePos = bitPos / 8;
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int bitInByte = bitPos % 8;
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if(bytePos < size) {
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data[bytePos] ^= (1 << bitInByte);
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// printf("纠正位置：字节 %d，位 %d\n", bytePos, bitInByte);
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return 1;
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}
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return -2; // 检测到多位错误
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}
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