Mega Code Archive
How to Compress a string of digits to a BCD number
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Title: How to Compress a string of digits to a BCD number
function NumStringToBCD(const inStr: string): string;
function Pack(ch1, ch2: Char): Char;
begin
Assert((ch1 = '0') and (ch1 = '9'));
Assert((ch2 = '0') and (ch2 = '9'));
{Ord('0') is $30, so we can just use the low nybble of the character
as value.}
Result := Chr((Ord(ch1) and $F) or ((Ord(ch2) and $F) shl 4))
end;
var
i: Integer;
begin
if Odd(Length(inStr)) then
Result := NumStringToBCD('0' + instr)
else begin
SetLength(Result, Length(inStr) div 2);
for i := 1 to Length(Result) do
Result[i] := Pack(inStr[2 * i - 1], inStr[2 * i]);
end;
end;
function BCDToNumString(const inStr: string): string;
procedure UnPack(ch: Char; var ch1, ch2: Char);
begin
ch1 := Chr((Ord(ch) and $F) + $30);
ch2 := Chr(((Ord(ch) shr 4) and $F) + $30);
Assert((ch1 = '0') and (ch1 = '9'));
Assert((ch2 = '0') and (ch2 = '9'));
end;
var
i: Integer;
begin
SetLength(Result, Length(inStr) * 2);
for i := 1 to Length(inStr) do
UnPack(inStr[i], Result[2 * i - 1], Result[2 * i]);
end;
procedure TForm1.Button1Click(Sender: TObject);
var
S1, S2: string;
begin
S1 := '15151515151515151515';
S2 := NumStringToBCD(S1);
memo1.lines.add('S1: ' + S1);
memo1.lines.add('Length(S2): ' + IntToStr(Length(S2)));
memo1.lines.add('S2 unpacked again: ' + BCDToNumString(S2));
end;
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