Signed hex string to a int

This is a discussion on Signed hex string to a int within the C Programming forums, part of the General Programming Boards category; Im trying to write a program to parse a list of hex strings. Each hex string is 2 bytes and ...

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    Signed hex string to a int

    Im trying to write a program to parse a list of hex strings. Each hex string is 2 bytes and represents a two complements number. I need a fast and efficient way to convert this to a integer. Files containing the hex string are 30-100mb so i need something very efficient. if someone can help me out that would be great.

    THX

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    C++まいる!Cをこわせ! Elysia's Avatar
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    A function that could convert hex to integer is strtol, I think.
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    Deathray Engineer MacGyver's Avatar
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    strtol() is probably the fastest way to do one number, as Elysia already suggested.

    However, if you know how many numbers to read and in what format, one of the family of scanf() function might be better.... but be aware of the issues of using scanf().

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    Quote Originally Posted by naruto267 View Post
    Im trying to write a program to parse a list of hex strings. Each hex string is 2 bytes and represents a two complements number. I need a fast and efficient way to convert this to a integer. Files containing the hex string are 30-100mb so i need something very efficient. if someone can help me out that would be great.
    Yep you have big files sizes. So what do you mean by being efficient? I feel that reading such big files will take bigger fractions of your time. So stop worrying about efficient converter function.

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    I believe your emphasis on efficiency is mis-guided.

    If you haven't timed or profiled working code, how do you know you even have an efficiency problem?

    Your bottleneck should be your HD reading the data.

    In any case, show us your code where you have tried this, and let's see what's needed. Don't just drop the "I need a program to do this and that, and it really needs to be efficient, too", post on us, and expect a program served up on a silver platter.

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    Well i took this lookup table code form somewhere and modified it a bit
    Code:
    signed short parseHex(char *value)
    {
    	int i,j;
    	typedef struct
    	{
    		char chr;
    		signed short value;
    	} CHexMap;
    	int HexMapL = 16;
    	CHexMap HexMap[] = 
    	{
    		{'0', 0}, {'1', 1}, {'2', 2}, {'3', 3},
    		{'4', 4}, {'5', 5}, {'6', 6}, {'7', 7},
    		{'8', 8}, {'9', 9}, {'A', 10}, {'B', 11},
    		{'C', 12}, {'D', 13}, {'E', 14}, {'F', 15}
    	};
    	signed short result = 0;
    	char *s = value;
    	for (j = 0; j < 4; j++)
    	{
    		result << 4;
    		for (i = 0; i < HexMapL; i++)
    	    {
    			if (*s == HexMap[i].chr)
    			{
    		        result |= HexMap[i].value;
    		        break;
    			}
    	    }
    		s++;
    	}
    	
    	return result;
    }

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