fluxengine/lib/crc.cc

#include "globals.h"
#include "bytes.h"
#include "crc.h"

template <class T>
T reflect(T bin, unsigned width = sizeof(T)*8)
{
	T bout = 0;
	while (width--)
	{
		bout <<= 1;
		bout |= (bin & 1);
		bin >>= 1;
	}
	return bout;
}

uint64_t generic_crc(const struct crcspec& spec, const Bytes& bytes)
{
	uint64_t crc = spec.init;
	uint64_t top = 1LL << (spec.width-1);
	uint64_t mask = (top<<1) - 1;

	for (uint8_t b : bytes)
	{
		if (spec.refin)
			b = reflect(b);

		for (uint8_t i = 0x80; i != 0; i >>= 1)
		{
			uint64_t bit = crc & top;
			crc <<= 1;
			if (b & i)
				bit ^= top;
			if (bit)
				crc ^= spec.poly;
		}
	}

	if (spec.refout)
		crc = reflect(crc, spec.width);
	crc ^= spec.xorout;
	return crc & mask;
}

uint16_t sumBytes(const Bytes& bytes)
{
	ByteReader br(bytes);

	uint16_t i = 0;
	while (!br.eof())
		i += br.read_8();
	return i;
}

uint8_t xorBytes(const Bytes& bytes)
{
	ByteReader br(bytes);

	uint8_t i = 0;
	while (!br.eof())
		i ^= br.read_8();
	return i;
}

uint16_t crc16(uint16_t poly, uint16_t crc, const Bytes& bytes)
{
	ByteReader br(bytes);

	while (!br.eof())
	{
		crc ^= br.read_8() << 8;
		for (int i=0; i<8; i++)
			crc = (crc & 0x8000) ? ((crc<<1)^poly) : (crc<<1);
	}

	return crc;
}

uint16_t crc16ref(uint16_t poly, uint16_t crc, const Bytes& bytes)
{
	ByteReader br(bytes);

	while (!br.eof())
	{
		crc ^= br.read_8();
		for (int i=0; i<8; i++)
			crc = (crc & 0x0001) ? ((crc>>1)^poly) : (crc>>1);
	}

	return crc;
}

/* Thanks to user202729 on StackOverflow for miraculously reverse engineering
 * this. */
uint32_t crcbrother(const Bytes& bytes)
{
	ByteReader br(bytes);

	uint32_t crc = br.read_8();
	while (!br.eof())
	{
		for (int i=0; i<8; i++)
			crc = (crc & 0x800000) ? ((crc<<1)^BROTHER_POLY) : (crc<<1);
		crc ^= br.read_8();
	}

	return crc & 0xFFFFFF;
}