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CRCUtil.cpp
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/*
* CRCUtil.cpp
*
* Created on: 31 Jul 2019
* Author: Michael Neuweiler
*/
#include "CRCUtil.h"
char16_t CRCUtil::crc_tb[] = { 0, 4129, 8258, 12387, 16516, 20645, 24774, 28903, 33032, 37161, 41290, 45419, 49548, 53677, 57806, 61935, 4657, 528,
12915, 8786, 21173, 17044, 29431, 25302, 37689, 33560, 45947, 41818, 54205, 50076, 62463, 58334, 9314, 13379, 1056, 5121, 25830, 29895, 17572,
21637, 42346, 46411, 34088, 38153, 58862, 62927, 50604, 54669, 13907, 9842, 5649, 1584, 30423, 26358, 22165, 18100, 46939, 42874, 38681,
34616, 63455, 59390, 55197, 51132, 18628, 22757, 26758, 30887, 2112, 6241, 10242, 14371, 51660, 55789, 59790, 63919, 35144, 39273, 43274,
47403, 23285, 19156, 31415, 27286, 6769, 2640, 14899, 10770, 56317, 52188, 64447, 60318, 39801, 35672, 47931, 43802, 27814, 31879, 19684,
23749, 11298, 15363, 3168, 7233, 60846, 64911, 52716, 56781, 44330, 48395, 36200, 40265, 32407, 28342, 24277, 20212, 15891, 11826, 7761, 3696,
65439, 61374, 57309, 53244, 48923, 44858, 40793, 36728, 37256, 33193, 45514, 41451, 53516, 49453, 61774, 57711, 4224, 161, 12482, 8419, 20484,
16421, 28742, 24679, 33721, 37784, 41979, 46042, 49981, 54044, 58239, 62302, 689, 4752, 8947, 13010, 16949, 21012, 25207, 29270, 46570, 42443,
38312, 34185, 62830, 58703, 54572, 50445, 13538, 9411, 5280, 1153, 29798, 25671, 21540, 17413, 42971, 47098, 34713, 38840, 59231, 63358,
50973, 55100, 9939, 14066, 1681, 5808, 26199, 30326, 17941, 22068, 55628, 51565, 63758, 59695, 39368, 35305, 47498, 43435, 22596, 18533,
30726, 26663, 6336, 2273, 14466, 10403, 52093, 56156, 60223, 64286, 35833, 39896, 43963, 48026, 19061, 23124, 27191, 31254, 2801, 6864, 10931,
14994, 64814, 60687, 56684, 52557, 48554, 44427, 40424, 36297, 31782, 27655, 23652, 19525, 15522, 11395, 7392, 3265, 61215, 65342, 53085,
57212, 44955, 49082, 36825, 40952, 28183, 32310, 20053, 24180, 11923, 16050, 3793, 7920 };
byte CRCUtil::byteBuf[] = { 0, 0, 0 };
CRCUtil::CRCUtil()
{
}
bool CRCUtil::checkCRC(String data)
{
if (data.length() < 3) {
return false;
}
String firstValue = data.substring(0, data.length() - 2);
String lastValue = data.substring(data.length() - 2);
int crcCalculated = calcCRC(firstValue);
int crcReceived = strtol(toHexString(lastValue).c_str(), NULL, 16);
return (crcReceived == crcCalculated);
}
byte* CRCUtil::getCRCByte(String data)
{
int crcint = calcCRC(data);
int crclow = crcint & 255;
int crchigh = crcint >> 8 & 255;
byteBuf[0] = crchigh;
byteBuf[1] = crclow;
return byteBuf;
}
String CRCUtil::getCRC(String data)
{
byte *b = getCRCByte(data);
b[3] = 0;
return String(reinterpret_cast<const char*>(b));
}
String CRCUtil::toHexString(String data)
{
String str = "";
for (unsigned int i = 0; i < data.length(); ++i) {
short ch = (short) data.charAt(i);
if (ch < 0) {
ch = (short) (ch + 256);
}
String s4 = String(ch, HEX);
if (s4.length() < 2) {
s4 = "0" + s4;
}
str += s4;
}
return str;
}
int CRCUtil::calcCRC(String data)
{
int len = data.length();
int i = 0;
int crc = 0;
while (len-- != 0) {
int da = 255 & (255 & crc >> 8) >> 4;
crc <<= 4;
da = 255 & (255 & (crc ^= crc_tb[255 & (da ^ data.charAt(i) >> 4)]) >> 8) >> 4;
crc <<= 4;
int temp = 255 & (da ^ (data.charAt(i) & 15));
crc ^= crc_tb[temp];
++i;
}
int bCRCLow = 255 & crc;
int bCRCHign = 255 & crc >> 8;
if (bCRCLow == 40 || bCRCLow == 13 || bCRCLow == 10)
++bCRCLow;
if (bCRCHign == 40 || bCRCHign == 13 || bCRCHign == 10)
++bCRCHign;
crc = (255 & bCRCHign) << 8;
return crc += bCRCLow;
}