Mega Code Archive
Base36 conversion
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Title: Base36 conversion
Question: I need to convert a series of DWords into a hashed string that can be used as a serial number.
Answer:
I had to write a license control for an application and needed to present a hashed string for the user that could be read over phone to a call-center support in able to pass importent license data from the application.
One way to do this is was to create a 20 byte long hardware profile that included CPU information - 2 bytes, MacID - 5 bytes, CRC32 checksum of windows username and company name - 8 bytes and the harddrive serial number. All this information was then needed to be passed to the support and checked for a valid license. One way to pass these 20 bytes was to convert them into five base36 values containing [A..Z] and [0..9] characters as represantation.
The resulting string would look something as:
"DFD3LQ-FSDE3Y-WXHU89-34KLAS-WELPWE"
Below you can find functions to convert numbers into base36 strings and back again.
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function NumToBase36(Value : DWord) : string;
const BaseType = 36;
Base36Table = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';
Var BaseIdx : Word;
begin
result := '';
repeat
BaseIdx := Value mod BaseType;
Value := Value div BaseType;
result := Base36Table[BaseIdx+1] + result;
until value = 0;
end;
function Base36ToNum(Base36 : string) : Dword;
const BaseType = 36;
Base36Table = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';
Var lp0,BaseIdx,Mult : integer;
begin
result := 0;
Mult := 1;
for lp0 := Length(Base36) downto 1 do begin
BaseIdx := pos(Upcase(Base36[lp0]),Base36Table)-1;
if BaseIdx inc(result,(BaseIdx*Mult));
Mult := Mult * BaseType;
end;
end;
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