Knowledge Base Nr: 00227 s5gleitpunkt.cpp - http://www.swe-kaiser.de

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S5 Gleitpunktzahlen nach IEEE

  
//das float-format der S5 ist anderes als bei S7 und PC
//der code wurde aus einem Siemens S7 Codesample AWL nach C übersetzt.

unsigned long CS7Koppel::DoZweierkomplement(unsigned long dwIn)
{
	//Eine Negation in diesem Zahlen-System entspricht einer bitweisen Invertierung,
	//gefolgt von einer Addition von 1, wobei jeder an der Stelle n entstehende Übertrag ignoriert wird.
	//Eine einfache Papier-und-Bleistift-Methode für die Negation übernimmt rechts beginnend jedes Bit
	//bis einschließlich der ersten auftretenden 1 und invertiert ab dieser Position alle nachfolgenden Bits.
	unsigned long dwOut = 0;
  bool bInvert = false;

	for (int b=0; b<32; b++)
	{
		if (bInvert)
			dwOut |= (dwIn&(1<<b)) ? 0 : (1<<b);
		else
			dwOut |= dwIn&(1<<b);

		if (dwIn&(1<<b))
			bInvert = true;
  }

	return dwOut;
}

float CS7Koppel::S5toIEEE(unsigned char b1, unsigned char b2, unsigned char b3, unsigned char b4, bool* bError)
{
	DEBUGOUT("S5toIEEE() %02x %02x %02x %02x", b1, b2, b3, b4);
	*bError = false;

	unsigned int nTmpData = 0;
	nTmpData |= (((int)b1<<24) & 0xFF000000);
	nTmpData |= (((int)b2<<16) & 0x00FF0000);
	nTmpData |= (((int)b3<<8)  & 0x0000FF00);
	nTmpData |= (((int)b4<<0)  & 0x000000FF);
	DEBUGOUT("S5toIEEE() 0x%08x", nTmpData);

	/////////////////////

	const float MAX_FLOAT = 1.701412e+38;

	bool bNeg = false;
	bool bS5Mbit = false;

	unsigned long dwS5temp = nTmpData;
	unsigned long dwS7temp = 0;

	unsigned long dw1Byte = (dwS5temp >> 24) & 0x000000FF;
	unsigned long dw2Byte = (dwS5temp >> 16) & 0x000000FF;

	if ((dw1Byte == 0x00000081) || (dw1Byte == 0x00000082))
	{
		*bError = true;
		LOG("ERROR: S5toIEEE(0x%08X) ausser Bereich!\n", nTmpData);
		return MAX_FLOAT;
	}

	if (dw2Byte & 0x80)
	{
		bNeg = true;
		dwS7temp = DoZweierkomplement(dwS5temp);
	}
	else
	{
		dwS7temp = dwS5temp;
	}

	dw1Byte = (dwS5temp >> 24) & 0x000000FF;
	dw2Byte = (dwS7temp >> 16) & 0x000000FF;
	if (dw2Byte & 0x40)
	{
		bS5Mbit = true;
	}

	dwS7temp <<= 1;
	dwS7temp &= 0x007FFFFF;

	unsigned long dwExponent = 0;

	bool bNorm = ((dwS7temp != 0) || (bS5Mbit == true));
	DEBUGOUT("S5toIEEE() dwS7temp=0x%08x bS5Mbit=%d bNorm=%d", dwS7temp, bS5Mbit, bNorm);

	if (!bNorm)
	{
		DEBUGOUT("S5toIEEE() dw1Byte=0x%08x bNeg=%d", dw1Byte, bNeg);
		if (dw1Byte == 0x80)
			return 0.0;
		else if ((dw1Byte == 0x00) && !bNeg)
			return 0.0;
		else
			dwExponent = dw1Byte + 127;
	}
	else  //norm
	{
		DEBUGOUT("S5toIEEE() norm: dw1Byte=0x%08x", dw1Byte);
		if (dw1Byte == 0x80)
		{
			*bError = true;
			LOG("ERROR: S5toIEEE(0x%08X) zu klein!\n", nTmpData);
			return MAX_FLOAT;
		}
		else
		{
			dwExponent = dw1Byte + 126;
		}
	}

	//gpt:
	dwExponent <<= 7;
	dwExponent &= 0xFF80;

	dwExponent <<= 16;
	dwS7temp += dwExponent;

	if (bNeg)
		dwS7temp |= 0x80000000;
	else
		dwS7temp &= ~0x80000000;

	float fData = 0.0;
	memcpy(&fData, &dwS7temp, 4);
	DEBUGOUT("S5toIEEE() fData=%g", fData);
	return fData;
}

unsigned long CS7Koppel::IEEEtoS5(float fData, bool* bError)
{
	*bError = false;

	unsigned int nTmpData = 0;
	memcpy(&nTmpData, &fData, 4);

	/////////////////////

	bool bNeg = false;

	unsigned long dwS7temp = nTmpData;
	unsigned long dwS5temp = 0;

	if (fData >= 1.701412e+38)
	{
		*bError = true;
		LOG("ERROR: IEEEtoS5(%g) >= 1.701412e+38\n", fData);
		return ~0;
	}

	if (fData <= -1.701412e+38)
	{
		*bError = true;
		LOG("ERROR: IEEEtoS5(%g) <= -1.701412e+38\n", fData);
		return ~0;
	}

	if (fData == 0.0)
		return 0x80000000;	//s5:0

	if (dwS7temp & 0x80000000)
		bNeg = true;

	dwS7temp <<= 1;

	unsigned long dw1Byte = (dwS7temp >> 24) & 0x000000FF;

	dwS5temp = (dw1Byte - 126) << 24;

	dwS7temp |= 0x01000000;
	dwS7temp &= ~0x02000000;
	dwS7temp >>= 2;

	if (bNeg)
		dwS7temp = DoZweierkomplement(dwS7temp);

	dwS7temp &= 0x00FFFFFF;
	dwS7temp += dwS5temp;
	return dwS7temp;
}