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COMMON: Remove the need for most reflecting when initing reflected table

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Instead reflect the polynomial and change the shifts. Also removes the
need for explicit init.

This makes our crc more similar to its standard implementation
This commit is contained in:
Vladimir Serbinenko 2022-11-27 17:38:05 +01:00 committed by Eugene Sandulenko
parent 35bac4e58c
commit 05f1a0df51
5 changed files with 49 additions and 51 deletions
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93
common/crc.h
View File

@ -45,7 +45,6 @@ template <typename T, bool need_reflect>
class CRCCommon {
public:
CRCCommon(T poly, T init_remainder, T final_xor);
T init(void);
T finalize(T remainder) const;
T crcSlow(byte const message[], int nBytes) const;
T getInitRemainder() const { return reflectRemainder(_init_remainder); }
@ -58,10 +57,6 @@ protected:
const int _width;
const int _topbit;
T _crcTable[256];
bool _inited;
template<typename R>
static R reflect(R data);
@ -72,19 +67,25 @@ protected:
template <typename T>
class CRCNormal : public CRCCommon<T, false> {
public:
CRCNormal(T poly, T init_remainder, T final_xor) : CRCCommon<T, false>(poly, init_remainder, final_xor) {}
CRCNormal(T poly, T init_remainder, T final_xor);
T crcFast(byte const message[], int nBytes) const;
T processByte(byte byteVal, T remainder) const;
private:
T _crcTable[256];
};
template <typename T>
class CRCReflected : public CRCCommon<T, true> {
public:
CRCReflected(T poly, T init_remainder, T final_xor) : CRCCommon<T, true>(poly, init_remainder, final_xor) {}
CRCReflected(T poly, T init_remainder, T final_xor);
T crcFast(byte const message[], int nBytes) const;
T processByte(byte byteVal, T remainder) const;
private:
T _crcTable[256];
};
/*********************************************************************
@ -169,29 +170,10 @@ T CRCCommon<T, need_reflect>::crcSlow(byte const message[], int nBytes) const {
template<typename T, bool need_reflect>
CRCCommon<T, need_reflect>::CRCCommon(T poly, T init_remainder, T final_xor) :
_poly(poly), _init_remainder(init_remainder), _final_xor(final_xor), _width(8 * sizeof(T)), _topbit(1 << (8 * sizeof(T) - 1)) {
_poly(poly), _init_remainder(init_remainder), _final_xor(final_xor), _width(8 * sizeof(T)), _topbit(1 << (8 * sizeof(T) - 1)) {}
for (int i = 0; i < 256; ++i)
_crcTable[i] = 0;
_inited = false;
}
/*********************************************************************
*
* Function: crcInit()
*
* Description: Populate the partial CRC lookup table.
*
* Notes: This function must be rerun any time the CRC standard
* is changed. If desired, it can be run "offline" and
* the table results stored in an embedded system's ROM.
*
* Returns: Initial remainder.
*
*********************************************************************/
template<typename T, bool need_reflect>
T CRCCommon<T, need_reflect>::init() {
template <typename T>
CRCNormal<T>::CRCNormal(T poly, T init_remainder, T final_xor) : CRCCommon<T, false>(poly, init_remainder, final_xor) {
/*
* Compute the remainder of each possible dividend.
*/
@ -199,7 +181,7 @@ T CRCCommon<T, need_reflect>::init() {
/*
* Start with the dividend followed by zeros.
*/
T remainder = dividend << (_width - 8);
T remainder = dividend << (this->_width - 8);
/*
* Perform modulo-2 division, a bit at a time.
@ -208,8 +190,8 @@ T CRCCommon<T, need_reflect>::init() {
/*
* Try to divide the current data bit.
*/
if (remainder & _topbit) {
remainder = (remainder << 1) ^ _poly;
if (remainder & this->_topbit) {
remainder = (remainder << 1) ^ this->_poly;
} else {
remainder = (remainder << 1);
}
@ -218,14 +200,43 @@ T CRCCommon<T, need_reflect>::init() {
/*
* Store the result into the table.
*/
_crcTable[reflectData(dividend)] = reflectRemainder(remainder);
}
_inited = true;
return _init_remainder;
this->_crcTable[dividend] = remainder;
}
}
template <typename T>
CRCReflected<T>::CRCReflected(T poly, T init_remainder, T final_xor) : CRCCommon<T, true>(poly, init_remainder, final_xor) {
T reflected_poly = this->reflectRemainder(poly);
/*
* Compute the remainder of each possible dividend.
*/
for (int dividend = 0; dividend < 256; ++dividend) {
/*
* Start with the dividend followed by zeros.
*/
T remainder = dividend;
/*
* Perform modulo-2 division, a bit at a time.
*/
for (byte bit = 8; bit > 0; --bit) {
/*
* Try to divide the current data bit.
*/
if (remainder & 1) {
remainder = (remainder >> 1) ^ reflected_poly;
} else {
remainder = (remainder >> 1);
}
}
/*
* Store the result into the table.
*/
_crcTable[dividend] = remainder;
}
}
/*********************************************************************
*
@ -242,9 +253,6 @@ template<typename T>
T CRCNormal<T>::crcFast(byte const message[], int nBytes) const {
T remainder = this->_init_remainder;
if (!this->_inited)
error("CRC::crcFast(): init method must be called first");
/*
* Divide the message by the polynomial, a byte at a time.
*/
@ -274,9 +282,6 @@ template<typename T>
T CRCReflected<T>::crcFast(byte const message[], int nBytes) const {
T remainder = this->reflectRemainder(this->_init_remainder);
if (!this->_inited)
error("CRC::crcFast(): init method must be called first");
/*
* Divide the message by the polynomial, a byte at a time.
*/

1
common/macresman.cpp
View File

@ -556,7 +556,6 @@ bool MacResManager::readAndValidateMacBinaryHeader(SeekableReadStream &stream, b
return false;
CRC_BINHEX crc;
crc.init();
uint16 checkSum = crc.crcFast(infoHeader, 124);
// Sanity check on the CRC. Some movies could look like MacBinary

1
common/unzip.cpp
View File

@ -1000,7 +1000,6 @@ public:
ZipArchive::ZipArchive(unzFile zipFile) : _zipFile(zipFile), _crc() {
assert(_zipFile);
_crc.init();
}
ZipArchive::~ZipArchive() {

1
engines/mtropolis/boot.cpp
View File

@ -760,7 +760,6 @@ static bool getMacTypesForMacBinary(const char *fileName, uint32 &outType, uint3
return false;
Common::CRC_BINHEX crc;
crc.init();
uint16 checkSum = crc.crcFast(mbHeader, 124);
if (checkSum != READ_BE_UINT16(&mbHeader[124]))

4
test/common/crc.h
View File

@ -12,7 +12,6 @@ class CrcTestSuite : public CxxTest::TestSuite
public:
void test_crc32() {
Common::CRC32 crc;
crc.init();
TS_ASSERT_EQUALS(crc.crcFast(testString, testLen), 0x414fa339U);
TS_ASSERT_EQUALS(crc.crcSlow(testString, testLen), 0x414fa339U);
uint32 running = crc.getInitRemainder();
@ -23,7 +22,6 @@ public:
void test_crc16() {
Common::CRC16 crc;
crc.init();
TS_ASSERT_EQUALS(crc.crcFast(testString, testLen), 0xfcdfU);
TS_ASSERT_EQUALS(crc.crcSlow(testString, testLen), 0xfcdfU);
uint16 running = crc.getInitRemainder();
@ -34,7 +32,6 @@ public:
void test_crc_ccitt() {
Common::CRC_CCITT crc; // aka ccitt-false
crc.init();
TS_ASSERT_EQUALS(crc.crcFast(testString, testLen), 0x8fddU);
TS_ASSERT_EQUALS(crc.crcSlow(testString, testLen), 0x8fddU);
uint16 running = crc.getInitRemainder();
@ -45,7 +42,6 @@ public:
void test_crc_binhex() {
Common::CRC_BINHEX crc; // Aka xmodem
crc.init();
TS_ASSERT_EQUALS(crc.crcFast(testString, testLen), 0xf0c8U);
TS_ASSERT_EQUALS(crc.crcSlow(testString, testLen), 0xf0c8U);
uint16 running = crc.getInitRemainder();