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Old 07-May-2004, 17:33
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Decimal to Hex conversion function

CPP / C++ / C Code:
using namespace std;

								Decimal to Hex converter

This is a template function which returns a char* array filled with hex digits when 
passed to it a number(can work as a decimal to hex conversion)and will work for signed 
and unsigned: char, short, and integer(long) type parameters passed to it. 

Shortcomings:It won't work for double because of presence of bitshifting in its algorithm.

Other uses: you can pass it a hex number and it will return that char* array filled
with the original hex digits.

template <class type>					//template usage to allow multiple types of parameters
char *type_char(type _num)
	char *hdigits;						//char array to store the result and return
	unsigned char size = sizeof(type)*2;//2 hex digits for each byte(8bits)
	hdigits = new char[size+2];			//first character for sign, last for null
	char *hlookup = "0123456789abcdef";	//lookup table stores the hex digits into their
										//corresponding index.
	type temp = _num;					//temporary place holder for _num of the same type
										//as _num
		hdigits[0]='-';					//if _num is negative make the sign negative
		_num *= -1;						//and make _num positive to clear(zero) the sign bit
		hdigits[0]=' ';					//else if _num is positive, make the sign blank(space)
	char mask = 0x000f;					//mask will clear(zero) out all the bits except lowest 4
										//which represent a single hex digit
The following for loop works this way: it starts with x as 0 and then right shifts
the temp number bits in multiples of x and 4. On the first pass, it won't shift(shift by 0)
because we need the lowest 4 bits for the lowest or right most hex digits. The next pass it
will right shift by 4(4*1), because we are done with the lowest 4 bits. Now we need the
4 bits higher than the lowest 4 bits, meaning bits 5-8 or 4-7 depending on how you count
from right. So we right shift by 4 bits pushing the bits 5-8(4-7) in to the lowest 4 bit
places, and then perform the AND operation on the number with our mask to clear(zero) all 
of the bits except the lowest 4. Then the number that the lowest 4 bits represent, will be
used as an index to fetch a hex digit from the lookup array. The loop will run till x has 
reached size(number of hex digit storage possible in the passed parameter type).

	for(char x=0;x<size;x++)
		temp = _num;					//temp is assigned _num each time
		temp >>=(4*x);					//shift it in multiples of 4 bits each time
		temp &= mask;					//mask the integer so it will only have lowest 4 bits
		hdigits[size-x]=hlookup[temp];	//temp now contains a numeric value which will point
										//to the corresponding index in the look up table so
										//all we have to do is use it as an index to the lookup
	hdigits[size+1]= NULL;				//the last element will store a null

	return hdigits;

int main()
	int _4byte;

	return 0;


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