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unique 48 bits number to unique 32 bits number

Hi,
as stated in the header, does anyone know an algorithm or something like that which enables me to use a 48 bit unique number and store it as a unique 32 bit number??
Regards

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sunnycoder

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rajeev_devin

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nafis_devlpr

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Axter

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itsmeandnobodyelse

Do you know the whole set of 48-bit numbers where the uniqueness needs to keep guaranteed ? If yes, you might take the index of each number as a unique 32 bit equivalence (I assume the size of the set is less than 4 billions).

If no, you could simply count the 4bit numbers you have to convert and and return the count value as a unique id:

typedef unsigned short UI48[3];

unsigned int I48ToI32(UI48 ui48)
{
static unsigned int count = 0;
return ++count;
}

In case you could get the same input twice you would need to store all numbers converted to a dictionary and check for existence before incrementing count.

struct UI48
{
unsigned short us3[3];
bool operator<(const UI48& u) const { return us3[0] < u.us3[0] ||
( us3[0] == u.us3[0] && us3[1] < u.us3[1]) ||
( us3[0] == u.us3[0] && us3[1] == u.us3[1] && us3[2] < u.us3[2]);
}
bool operator==(const UI48& u) const { return ( us3[0] == u.us3[0] && us3[1] == u.us3[1] && us3[2] == u.us3[2]); }
};

unsigned int I48ToI32(UI48 ui48)
{
static unsigned int count = 0;
static std::map<UI48, unsigned int> uimap;
if (uimap.find(ui48) == uimap.end())
uimap[ui48] = ++count;
return uimap[ui48];
}

Regards, Alex

Infinity08

First of all : what do you want to achieve ?

1) lossless compression : impossible as stated by sunnycoder (unless there are max. 2^32 valid values possible for the 48bit integer)

2) conversion of a 48bit value to a 32bit value : only possible if the maximum value of the 48bit integer is 2^32-1

3) something else : please specify