Converting a float to a string

      
union Float
	{
	float f;
	struct 
		{
		unsigned int mantissa:23;
		unsigned int exponent:8;
		unsigned int sign:1;
		};
	};

void ftoa(char* s, float f_, int decimals=4)
	{
	Float f;
	f.f = f_;
	int exp = unsigned char(f.exponent + 128);
	int man = 0x00800000 | f.mantissa;
	
	unsigned char pbcd[10];
	unsigned char bcd[18];
	
	if(0xff==f.exponent)
		{//Special Case

		if(f.mantissa)
			{//Not A Number

			if(f.mantissa&0x00400000)
				*s = 'Q';//Undefined Result

			else
				*s= 'S';//Invalid Operand/Operation

			s++;
			strcpy(s, "NaN");
			return;
			}
		else
			{//Infinity

			if(f.sign)
				{
				*s = '-';
				s++;
				}
			strcpy(s, "Inf");
			return;
			}
		}
	
	if(!f.exponent)
		{
		if(!f.mantissa)
			{//Zero is Special

			if(f.sign)
				{
				*s = '-';
				s++;
				}
			*s = '0';
			++s;
			*s = '.';
			++s;
			for(int i=0; i<decimals; ++i)
				s[i] = '0';
			return;
			}
		else
			{//Denormalize

			man &= 0x007fffff;
			}
		}
	
	if(f.sign)
		{
		*s = '-';
		s++;
		}
	
	//Calculate scaling factor as dictated by the desired decimal output

	int scale=1;
	for(int i=0; i<decimals; ++i)
		scale*=10;
	
	//Convert float into packed BCD

	//scale by factor (neccessary to extract decimal digits)

	#pragma warning(disable:4409)
	__asm
		{
		fld f_
		fimul scale
		fbstp [pbcd]
		}
	
	//Unpack BCD

	unsigned char* d=&bcd[0];
	unsigned char* p=&pbcd[0];
	for(;p<&pbcd[10]; ++p)
		{
		*d = *p;
		*d &= 0x0F;
		++d;
		*d = *p;
		*d >>= 4;
		++d;
		}
	
	//Convert BCD to string

	//skip leading zeros before the decimal point

	//_but print at least a 0 before it (+1)

	for(d=&bcd[18]; d>=&bcd[decimals+1]; --d)
		{
		if(*d!=0)
			break;
		}
	//digits before the decimal

	for(; d>=&bcd[decimals]; --d)
		{
		*s = *d + '0';
		s++;
		}
	*s = '.';
	++s;
	//digits after the decimal

	for(; d>=&bcd[0]; --d)
		{
		*s = *d + '0';
		s++;
		}
	*s =0;
	}