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Efficiently convert between Hex, Binary, and Decimal in C/C++

Asked 2009-05-04T09:43:47.797
9

I have 3 base representations for positive integer numbers:

  1. Decimal, in unsigned long variable (e.g. unsigned long int NumDec = 200).
  2. Hex, in string variable (e.g. string NumHex = "C8")
  3. Binary, in string variable (e.g. string NumBin = "11001000")

I want to be able to convert between numbers in all 3 representations in the most efficient way. I.e. to implement the following 6 functions:

unsigned long int Binary2Dec(const string & Bin) {}
unsigned long int Hex2Dec(const string & Hex) {}
string Dec2Hex(unsigned long int Dec) {}
string Binary2Hex(const string & Bin) {}
string Dec2Binary(unsigned long int Dec) {}
string Hex2Binary(const string & Hex) {}

What is the most efficient approach for each of them? I can use C and C++, but not boost.

Edit: By "efficiency" I mean time efficiency: Shortest execution time.

c++ c binary decimal hex
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Why do these routines have to be so time-efficient? That sort of claim always makes me wonder. Are you sure the obvious conversion methods like strtol() are too slow, or that you can do better? System functions are usually pretty efficient. They are sometimes slower to support generality and error-checking, but you need to consider what to do with errors. If a bin argument has characters other than '0' and '1', what then? Abort? Propagate massive errors?

Why are you using "Dec" to represent the internal representation? Dec, Hex, and Bin should be used to refer to the string representations. There's nothing decimal about an unsigned long. Are you dealing with strings showing the number in decimal? If not, you're confusing people here and are going to confuse many more.

The transformation between binary and hex text formats can be done quickly and efficiently, with lookup tables, but anything involving decimal text format will be more complicated.

answered 2009-05-04T16:45:09.343

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