Base256 to int

Posted on 2006-10-24
Last Modified: 2008-02-01
Does anybody know how to convert a string (base 256 number) to integer?
Question by:TiborKi
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Accepted Solution

2266180 earned 125 total points
ID: 17796908
LVL 45

Expert Comment

ID: 17798414
How big is the string?
The ciuly link is probably the easiest solution.

Author Comment

ID: 17798517
the string is 4 bytes
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LVL 45

Expert Comment

ID: 17798626
The only problem you are likely to encounter is signed versus unsigned integer values.  If the high-order bit of the high-order byte = 1 then a signed integer will be negative.

Is this a performance critical function or do you simply need to know how it can be done?

Author Comment

ID: 17798790
well, it must be fast...
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Assisted Solution

aikimark earned 125 total points
ID: 17798999
"fast" is relative.  The best course of action will be to try the ciuly linked solution and determine if it suits your needs as far as functionality and speed.  If it doesn't, then ask us for more help.

For future readers, there are several approaches available to do this conversion.
* character->ord add and shiftLeft 8 (three statement pairs followed by simple add)
* similar to above, but using For iteration construct
* Delphi Copy function or API call to copy bytes directly into integer variable.  May require additional ntohl API call to reverse the byte order to accomodate Little-endian Windows environment.  This solution can get really tricky, depending on the nature of the 'string variable'.  Due to complexity, this should be solution approach of last resort.
* ASM solution (see the FastCode project)

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