procedure TForm1.Button1Click(Sender: TObject);
var
xlap,xlbook,xlsheet:variant;
y:integer;
begin
xlap:=createoleobject('excel.application');
xlbook:=xlap.workbooks.add;
xlap.visible:=true;
xlsheet:=xlbook.worksheets.add;
for y:=1 to 50 do
begin
xlsheet.cells[y,2].value:= concat('=IF(A',y,'>6,"Good","Bad")')
inc(y);
end;
end;
That's my code to make an Excel through Delphi. I want to input the IF formula into column B of the Excel, but there is error when I use the concat('=IF(A',y,'>6,"Good","Bad")').
May be I need another way to include y between those strings.
Any suggestion? Thanks before
Delphi has a format statement bit like sprintf printf in c, well nearly
xlsheet.cells[y,2].value:= format('=IF(A%d>6,"Good", "Bad")',[y])
%d is a place holder for an int. Look it up for loads of other stuff.
NB the variables you want to interpolate are assed in an array.
In addition to Tony's answer about Format, here are a couple of other approaches. (Format is great if you have mixed types or many values, but it carries some overhead that might not be needed.)
You can concatenate strings with a simple + - in fact, the Concat documentation says it does the same thing but is faster:
Temp := 'ing';
Str := 'Test' + Temp; // Str = 'Testing'
As your y variable is an integer, you'll need to convert it to a string first (note you don't need to Inc(y);, as the loop will do that already - it's automatically incremented from the starting value to the ending value on each pass through the loop):
for y:=1 to 50 do
begin
xlsheet.cells[y,2].value:= '=IF(A' + IntToStr(y) + '>6,"Good","Bad")';
end;
I have a binary file (2.5 MB) and I want to find position of this sequence of bytes: CD 09 D9 F5. Then I want to write some data after this position and also overwrite old data (4 KB) with zeros.
Here is how I do it now but it is a bit slow.
ProcessFile(dataToWrite: string);
var
fileContent: string;
f: file of char;
c: char;
n, i, startIndex, endIndex: integer;
begin
AssignFile(f, 'file.bin');
reset(f);
n := FileSize(f);
while n > 0 do
begin
Read(f, c);
fileContent := fileContent + c;
dec(n);
end;
CloseFile(f);
startindex := Pos(Char($CD)+Char($09)+Char($D9)+Char($F5), fileContent) + 4;
endIndex := startIndex + 4088;
Seek(f, startIndex);
for i := 1 to length(dataToWrite) do
Write(f, dataToWrite[i]);
c := #0;
while (i < endIndex) do
begin
Write(f, c); inc(i);
end;
CloseFile(f);
end;
See this answer: Fast read/write from file in delphi
Some options are:
memory mapped files
TFileStream
blockread
To search the file buffer, see Best way to find position in the Stream where given byte sequence starts - one answer mentions the Boyer-Moore algorithm for fast detection of a byte sequence.
Your code to read the entire file into a string is very wasteful. Pascal I/O uses buffering so I don't think it's the byte by byte aspect particularly. Although one big read would be better. The main problem will be the string concatenation and the extreme heap allocation demand required to concatenate the string, one character at a time.
I'd do it like this:
function LoadFileIntoString(const FileName: string): string;
var
Stream: TFileStream;
begin
Stream := TFileStream.Create(FileName, fmOpenRead);
try
SetLength(Result, Stream.Size);//one single heap allocation
Stream.ReadBuffer(Pointer(Result)^, Length(Result));
finally
Stream.Free;
end;
end;
That alone should make a big difference. When it comes to writing the file, a similar use of strings will be much faster. I've not attempted to decipher the writing part of your code. Writing the new data, and the block of zeros again should be batched up to as few separate writes as possible.
If ever you find that you need to read or write very small blocks to a file, then I offer you my buffered file streams: Buffered files (for faster disk access).
The code could be optimised further to read only a portion of the file, and search until you find the target. You may be able to avoid reading the entire file that way. However, I suspect that these changes will make enough of a difference.
I'm one of those so-called developers who got their way with Delphi without really understanding or even thinking about basics. In this case, I'm talking about strings.
While I do understand how pre-allocating memory can result in a significant speed gain. I don't understand how to use it in simple, real-world, cases (this is even more true with the TStringBuilder).
For example, let's say I have this code that recursively search a folder & add results to a hash list:
var
FilesList : TDictionary<String, Byte>; // Byte = (file = 0, folder = 1)
// ------------------------------------------------------------------------------ //
procedure AddFolder(const AFolderName : String);
var
FileName : String;
AHandle : THandle;
FindData : TWin32FindData;
begin
AHandle := FindFirstFile(PChar(AFolderName + '*'), FindData);
if (AHandle = INVALID_HANDLE_VALUE) then
Exit;
repeat
if (FindData.dwFileAttributes And FILE_ATTRIBUTE_DIRECTORY = 0) then
begin
{ Add a file. }
FileName := FindData.cFileName;
FilesList.Add(AFolderName + FileName, 0);
end
else if ((FindData.cFileName[0] <> '.') OR Not ((FindData.cFileName[1] = #0) OR (FindData.cFileName[1] = '.') And (FindData.cFileName[2] = #0))) then
begin
FileName := AFolderName + FindData.cFileName + '\';
FilesList.Add(FileName, 1);
AddFolder(FileName);
end;
until Not FindNextFile(AHandle, FindData);
Windows.FindClose(AHandle);
end;
I'm not sure if it's a good example, but in this case, it's not clear to me how pre-allocating memory to the variable FileName would help increase the execution speed, especially that I know nothing about its length. Assuming this is possible, how?
Or is the pre-allocation technique only useful when concatenating / building strings?
Notes about my question:
The question is primarily for XE2, but feel free to reference other delphi versions as I'm sure other developers will benefit from sharing the wisdom (that is, assuming mods won't delete it as chatty or subjective)
I'm more interested in simple everyday cases where one needs to make micro-optimization in very large loops / with huge amount of data by optimizing string memory pre-allocation.
Straight up string concatenation (for example) can be slow because the memory for the string is reallocated for each piece that is appended. Sometimes the new size can actually be accommodated in place but sometimes the data must be copied to a new location, the old buffer freed, and so on. This takes time.
In general, though, this should be of no concern to you unless you have verified with a performance profiler or explicit timing statements that you do in fact have a performance issue.
Of course you got away without understanding how Strings really work: Delphi is grate in that respect, it's string manipulation is highly effective and it's memory-manager is also highly-effective for small memory blocks. You can do ALOT with Delphi and not have a problem with String manipulation.
There are some classes of problems where you should take care, especially if the routines you're looking at are to be reused (library code).
For example, this should always raise a flag:
Result := '';
for i:=1 to N do
Result := Result + Something; // <- Recursively builds the string, one-char-at-a-time
Even THAT might fly with Delphi, if it's not often use or is used where time is not critical. None the less that kind of code should be optimized so the entire (likely) length of the string is pre-allocated, then trimmed in then end:
SetLength(Result, Whatever);
for i:=1 to N do
Result[i] := SomeChar;
SetLength(Result, INowKnowTheLength);
Now for an example where the TStringBuilder shines. If you have something like this:
var Msg: string;
begin
Msg := 'Mr ' + MrName + #13#10;
if SomeCondition then
Msg := Msg + 'We were unable to reach you'
else
Msg := Msg + 'We need to let you know';
Msg := Msg + #13#10
end;
i.e: code that builds one complex (and possibly large) bit of message, then you can easily optimize it using TStringBuilder:
var Msg: TStringBuilder;
begin
Msg := TStringBuilder.Create;
try
Msg.Append('Mr ');
Msg.Append(MrName);
Msg.Append(#13#10);
if SomeCondition then
Msg.Append('We were unable to reach you')
else
Msg.Append('We need to let you know');
Msg.Append(#13#10);
ShowMessage(Msg.ToString); // <- Gets the whole string
finally Msg.Free;
end;
end;
Any way, always balance the ease of writing, ease of maintenance with the true benefits of the performance. Don't exceed natural limits for the code your write: optimizing a string-generating routine to be faster then the HDD can write is wasted effort. Optimizing some GUI code to generate a message in 1ms (instead of 20ms) is also wasted effort - the user would never know your code was 20 times faster, it'd be just as instantaneous.
Basically it is these concatenations you are talking about:
AFolderName + '*'
AFolderName + FindData.cFileName
AFolderName + FindData.cFileName + '\'
The first one is done once, the loop executes either the second and third.
These methods in System.pas are used internally for the 3 lines:
procedure _UStrCat3(var Dest: UnicodeString; const Source1, Source2: UnicodeString);
procedure _UStrCat3(var Dest: UnicodeString; const Source1, Source2: UnicodeString);
procedure _UStrCatN(var Dest: UnicodeString; ArgCnt: Integer; const Strs: UnicodeString); varargs;
Since the 3 values are different, you cannot optimize it using only one expression.
All functions precalculate the final length and do the proper allocation work if needed.
Inside the loop, you might try to do the preallocation of the AFolderName + FindData.cFileName + '\' yourself, and snap out the AFolderName + FindData.cFileName portion, but then you require 2 allocations for the then case.
So I think your code cannot get optimized much further (i.e. you cannot get it to perform an order of magnitude better).
In my program, I process millions of strings that have a special character, e.g. "|" to separate tokens within each string. I have a function to return the n'th token, and this is it:
function GetTok(const Line: string; const Delim: string; const TokenNum: Byte): string;
{ LK Feb 12, 2007 - This function has been optimized as best as possible }
var
I, P, P2: integer;
begin
P2 := Pos(Delim, Line);
if TokenNum = 1 then begin
if P2 = 0 then
Result := Line
else
Result := copy(Line, 1, P2-1);
end
else begin
P := 0; { To prevent warnings }
for I := 2 to TokenNum do begin
P := P2;
if P = 0 then break;
P2 := PosEx(Delim, Line, P+1);
end;
if P = 0 then
Result := ''
else if P2 = 0 then
Result := copy(Line, P+1, MaxInt)
else
Result := copy(Line, P+1, P2-P-1);
end;
end; { GetTok }
I developed this function back when I was using Delphi 4. It calls the very efficient PosEx routine that was originally developed by Fastcode and is now included in the StrUtils library of Delphi.
I recently upgraded to Delphi 2009 and my strings are all Unicode. This GetTok function still works and still works well.
I have gone through the new libraries in Delphi 2009 and there are many new functions and additions to it.
But I have not seen a GetToken function like I need in any of the new Delphi libraries, in the various fastcode projects, and I can't find anything with a Google search other than Zarko Gajic's: Delphi Split / Tokenizer Functions, which is not as optimized as what I already have.
Any improvement, even 10% would be noticeable in my program. I know an alternative is StringLists and to always keep the tokens separate, but this has a big overhead memory-wise and I'm not sure if I did all that work to convert whether it would be any faster.
Whew. So after all this long winded talk, my question really is:
Do you know of any very fast implementations of a GetToken routine? An assembler optimized version would be ideal?
If not, are there any optimizations that you can see to my code above that might make an improvement?
Followup: Barry Kelly mentioned a question I asked a year ago about optimizing the parsing of the lines in a file. At that time I hadn't even thought of my GetTok routine which was not used for the that read or parsing. It is only now that I saw the overhead of my GetTok routine which led me to ask this question. Until Carl Smotricz and Barry's answers, I had never thought of connecting the two. So obvious, but it just didn't register. Thanks for pointing that out.
Yes, my Delim is a single character, so obviously I have some major optimization I can do. My use of Pos and PosEx in the GetTok routine (above) blinded me to the idea that I can do it faster with a character by character search instead, with bits of code like:
while (cp^ > #0) and (cp^ <= Delim) do
Inc(cp);
I'm going to go through everyone's answers and try the various suggestions and compare them. Then I'll post the results.
Confusion: Okay, now I'm really perplexed.
I took Carl and Barry's recommendation to go with PChars, and here is my implementation:
function GetTok(const Line: string; const Delim: string; const TokenNum: Byte): string;
{ LK Feb 12, 2007 - This function has been optimized as best as possible }
{ LK Nov 7, 2009 - Reoptimized using PChars instead of calls to Pos and PosEx }
{ See; https://stackoverflow.com/questions/1694001/is-there-a-fast-gettoken-routine-for-delphi }
var
I: integer;
PLine, PStart: PChar;
begin
PLine := PChar(Line);
PStart := PLine;
inc(PLine);
for I := 1 to TokenNum do begin
while (PLine^ <> #0) and (PLine^ <> Delim) do
inc(PLine);
if I = TokenNum then begin
SetString(Result, PStart, PLine - PStart);
break;
end;
if PLine^ = #0 then begin
Result := '';
break;
end;
inc(PLine);
PStart := PLine;
end;
end; { GetTok }
On paper, I don't think you can do much better than this.
So I put both routines to the task and used AQTime to see what's happening. The run I had included 1,108,514 calls to GetTok.
AQTime timed the original routine at 0.40 seconds. The million calls to Pos took 0.10 seconds. A half a million of the TokenNum = 1 copies took 0.10 seconds. The 600,000 PosEx calls only took 0.03 seconds.
Then I timed my new routine with AQTime for the same run and exactly the same calls. AQTime reports that my new "fast" routine took 3.65 seconds, which is 9 times as long. The culprit according to AQTime was the first loop:
while (PLine^ <> #0) and (PLine^ <> Delim) do
inc(PLine);
The while line, which was executed 18 million times, was reported at 2.66 seconds. The inc line, executed 16 million times, was said to take 0.47 seconds.
Now I thought I knew what was happening here. I had a similar problem with AQTime in a question I posed last year: Why is CharInSet faster than Case statement?
Again it was Barry Kelly who clued me in. Basically, an instrumenting profiler like AQTime does not necessarily do the job for microoptimization. It adds an overhead to each line which may swamp the results which is shown clearly in these numbers. The 34 million lines executed in my new "optimized code" overwhelm the several million lines of my original code, with apparently little or no overhead from the Pos and PosEx routines.
Barry gave me a sample of code using QueryPerformanceCounter to check that he was correct, and in that case he was.
Okay, so let's do the same now with QueryPerformanceCounter to prove that my new routine is faster and not 9 times slower as AQTime says it is. So here I go:
function TimeIt(const Title: string): double;
var i: Integer;
start, finish, freq: Int64;
Seconds: double;
begin
QueryPerformanceCounter(start);
for i := 1 to 250000 do
GetTokOld('This is a string|that needs|parsing', '|', 1);
for i := 1 to 250000 do
GetTokOld('This is a string|that needs|parsing', '|', 2);
for i := 1 to 250000 do
GetTokOld('This is a string|that needs|parsing', '|', 3);
for i := 1 to 250000 do
GetTokOld('This is a string|that needs|parsing', '|', 4);
QueryPerformanceCounter(finish);
QueryPerformanceFrequency(freq);
Seconds := (finish - start) / freq;
Result := Seconds;
end;
So this will test 1,000,000 calls to GetTok.
My old procedure with the Pos and PosEx calls took 0.29 seconds.
The new one with PChars took 2.07 seconds.
Now I am completely befuddled! Can anyone tell me why the PChar procedure is not only slower, but is 8 to 9 times slower!?
Mystery solved! Andreas said in his answer to change the Delim parameter from a string to a Char. I'll always be using just a Char, so at least for my implementation this is very possible. I was amazed at what happened.
The time for the 1 million calls went down from 1.88 seconds to .22 seconds.
And surprisingly, the time for my original Pos/PosEx routine went UP from .29 to .44 seconds when I changed it's Delim parameter to a Char.
Frankly, I'm disappointed by Delphi's optimizer. That Delim is a constant parameter. The optimizer should have noticed that the same conversion is happening within the loop and should have moved it out so that it would only be done once.
Double checking my Code generation parameters, yes I do have Optimization True and String format checking Off.
Bottom line is that the new PChar routine with Andrea's fix is about 25% faster than my original (.22 versus .29).
I still want to follow up on the other comments here and test them out.
Turning off optimization and turning on String format checking only increases the time from .22 to .30. It adds about the same to the original.
The advantage to using assembler code, or calling routines written in assembler like Pos or PosEx is that they are NOT subject to what code generation options you have set. They will always run the same way, a pre-optimized and non-bloated way.
I have reaffirmed in the last couple of days, that the best way to compare code for microoptimization is to look at and compare the Assembler code in the CPU window. It would be nice if Embarcadero could make that window a bit more convenient, and allow us to copy portions to the clipboard or to print sections of it.
Also, I unfairly slammed AQTime earlier in this post, thinking that the extra time added for my new routine was solely because of the instrumentation it added. Now that I go back and check with the Char parameter instead of String, the while loop is down to .30 seconds (from 2.66) and the inc line is down to .14 seconds (from .47). Strange that the inc line would go down as well. But I'm getting worn out from all this testing already.
I took Carl's idea of looping by characters, and rewrote that code with that idea. It makes another improvement, down to .19 seconds from .22. So here is now the best so far:
function GetTok(const Line: string; const Delim: Char; const TokenNum: Byte): string;
{ LK Nov 8, 2009 - Reoptimized using PChars instead of calls to Pos and PosEx }
{ See; https://stackoverflow.com/questions/1694001/is-there-a-fast-gettoken-routine-for-delphi }
var
I, CurToken: Integer;
PLine, PStart: PChar;
begin
CurToken := 1;
PLine := PChar(Line);
PStart := PLine;
for I := 1 to length(Line) do begin
if PLine^ = Delim then begin
if CurToken = TokenNum then
break
else begin
CurToken := CurToken + 1;
inc(PLine);
PStart := PLine;
end;
end
else
inc(PLine);
end;
if CurToken = TokenNum then
SetString(Result, PStart, PLine - PStart)
else
Result := '';
end;
There still may be some minor optimizations to this, such as the CurToken = Tokennum comparison, which should be the same type, Integer or Byte, whichever is faster.
But let's say, I'm happy now.
Thanks again to the StackOverflow Delphi community.
It makes a big difference what "Delim" is expected to be. If it's expected to be a single character, you're far better off stepping through the string character by character, ideally through a PChar, and testing specifically.
If it's a long string, Boyer-Moore and similar searches have a set-up phase for skip tables, and the best way would be to build the tables once, and reuse them for each subsequent find. That means you need state between calls, and this function would be better off as a method on an object instead.
You might be interested in this answer I gave to a question some time before, about the fastest way to parse a line in Delphi. (But I see that it is you that asked the question! Nevertheless, in solving your problem, I would hew to how I described parsing, not using PosEx like you are using, depending on what Delim normally looks like.)
UPDATE: OK, I spent about 40 minutes looking at this. If you know the delimiter is going to be a character, you're pretty much always better off with the second version (i.e. PChar scanning), but you have to pass Delim as a character. At the time of writing, you're converting the PLine^ expression - of type Char - to a string for comparison with Delim. That will be very slow; even indexing into the string, with Delim[1] will also be somewhat slow.
However, depending on how large your lines are, and how many delimited pieces you want to pull out, you may be better off with a resumable approach, rather than skipping unwanted delimited pieces inside the tokenizing routine. If you call GetTok with successively increasing indexes, like you are currently doing in your mini benchmark, you'll end up with O(n*n) performance, where n is the number of delimited sections. That can be turned into O(n) if you save the state of the scan and restore it for the next iteration, or pack all extracted items into an array.
Here's a version that does all tokenization once, and returns an array. It needs to tokenize twice though, in order to know how large to make the array. On the other hand, only the second tokenization needs to extract the strings:
// Do all tokenization up front.
function GetTok4(const Line: string; const Delim: Char): TArray<string>;
var
cp, start: PChar;
count: Integer;
begin
// Count sections
count := 1;
cp := PChar(Line);
start := cp;
while True do
begin
if cp^ <> #0 then
begin
if cp^ <> Delim then
Inc(cp)
else
begin
Inc(cp);
Inc(count);
end;
end
else
begin
Inc(count);
Break;
end;
end;
SetLength(Result, count);
cp := start;
count := 0;
while True do
begin
if cp^ <> #0 then
begin
if cp^ <> Delim then
Inc(cp)
else
begin
SetString(Result[count], start, cp - start);
Inc(cp);
Inc(count);
end;
end
else
begin
SetString(Result[count], start, cp - start);
Break;
end;
end;
end;
Here's the resumable approach. The loads and stores of the current position and delimiter character do have a cost, though:
type
TTokenizer = record
private
FSource: string;
FCurrPos: PChar;
FDelim: Char;
public
procedure Reset(const ASource: string; ADelim: Char); inline;
function GetToken(out AResult: string): Boolean; inline;
end;
procedure TTokenizer.Reset(const ASource: string; ADelim: Char);
begin
FSource := ASource; // keep reference alive
FCurrPos := PChar(FSource);
FDelim := ADelim;
end;
function TTokenizer.GetToken(out AResult: string): Boolean;
var
cp, start: PChar;
delim: Char;
begin
// copy members to locals for better optimization
cp := FCurrPos;
delim := FDelim;
if cp^ = #0 then
begin
AResult := '';
Exit(False);
end;
start := cp;
while (cp^ <> #0) and (cp^ <> Delim) do
Inc(cp);
SetString(AResult, start, cp - start);
if cp^ = Delim then
Inc(cp);
FCurrPos := cp;
Result := True;
end;
Here's the full program I used for benchmarking.
Here are the results:
*** count=3, Length(src)=200
GetTok1: 595 ms
GetTok2: 547 ms
GetTok3: 2366 ms
GetTok4: 407 ms
GetTokBK: 226 ms
*** count=6, Length(src)=350
GetTok1: 1587 ms
GetTok2: 1502 ms
GetTok3: 6890 ms
GetTok4: 679 ms
GetTokBK: 334 ms
*** count=9, Length(src)=500
GetTok1: 3055 ms
GetTok2: 2912 ms
GetTok3: 13766 ms
GetTok4: 947 ms
GetTokBK: 446 ms
*** count=12, Length(src)=650
GetTok1: 4997 ms
GetTok2: 4803 ms
GetTok3: 23021 ms
GetTok4: 1213 ms
GetTokBK: 543 ms
*** count=15, Length(src)=800
GetTok1: 7417 ms
GetTok2: 7173 ms
GetTok3: 34644 ms
GetTok4: 1480 ms
GetTokBK: 653 ms
Depending on the characteristics of your data, whether the delimiter is likely to be a character or not, and how you work with it, different approaches may be faster.
(I made a mistake in my earlier program, I wasn't measuring the same operations for each style of routine. I updated the pastebin link and benchmark results.)
Your new function (the one with PChar) should declare "Delim" as Char and not as String. In your current implementation the compiler has to convert the PLine^ char into a string to compare it with "Delim". And that happens in a tight loop resulting is an enormous performance hit.
function GetTok(const Line: string; const Delim: Char{<<==}; const TokenNum: Byte): string;
{ LK Feb 12, 2007 - This function has been optimized as best as possible }
{ LK Nov 7, 2009 - Reoptimized using PChars instead of calls to Pos and PosEx }
{ See; http://stackoverflow.com/questions/1694001/is-there-a-fast-gettoken-routine-for-delphi }
var
I: integer;
PLine, PStart: PChar;
begin
PLine := PChar(Line);
PStart := PLine;
inc(PLine);
for I := 1 to TokenNum do begin
while (PLine^ <> #0) and (PLine^ <> Delim) do
inc(PLine);
if I = TokenNum then begin
SetString(Result, PStart, PLine - PStart);
break;
end;
if PLine^ = #0 then begin
Result := '';
break;
end;
inc(PLine);
PStart := PLine;
end;
end; { GetTok }
Delphi compiles to VERY efficient code; in my experience, it was very difficult to do better in assembler.
I think you should just point a PChar (they still exist, don't they? I parted ways with Delphi around 4.0) at the beginning of the string and increment it while counting "|"s, until you've found n-1 of them. I suspect that will be faster than calling PosEx repeatedly.
Take note of that position, then increment the pointer some more until you hit the next pipe. Pull out your substring. Done.
I'm only guessing, but I wouldn't be surprised if this was close to the quickest this problem can be solved.
EDIT: Here's what I had in mind. This code is, alas, uncompiled and untested, but it should demonstrate what I meant.
In particular, Delim is treated as a single char, which I believe makes a world of difference if that will fulfill the requirements, and the character at PLine is tested only once. Finally, there's no more comparison against TokenNum; I believe it's faster to decrement a counter to 0 for counting delimiters.
function GetTok(const Line: string; const Delim: string; const TokenNum: Byte): string;
var
Del: Char;
PLine, PStart: PChar;
Nth, I, P0, P9: Integer;
begin
Del := Delim[1];
Nth := TokenNum + 1;
P0 := 1;
P9 := Line.length + 1;
PLine := PChar(line);
for I := 1 to P9 do begin
if PLine^ = Del then begin
if Nth = 0 then begin
P9 := I;
break;
end;
Dec(Nth);
if Nth = 0 then P0 := I + 1
end;
Inc(PLine);
end;
if (Nth <= 1) or (TokenNum = 1) then
Result := Copy(Line, P0, P9 - P0);
else
Result := ''
end;
Using assembler would be a micro-optimization. There are much greater gains to be had by optimizing the algorithm. Not doing work beats doing work in the fastest possible way, every time.
One example would be if you have places in your program where you need several tokens of the same line. Another procedure that returns an array of tokens which you can then index into should be faster than calling your function more than once, especially if you let the procedure not return all tokens, but only as many as you need.
But in general I agree with Carl's answer (+1), using a PChar for scanning would probably be faster than your current code.
This is a function that I've had in my personal library for quite some time that I use extensively. I believe this is the most current version of it. I've had multiple versions in the past being optimized for a variety of different reasons. This one tries to take into account Quoted strings, but if that code is removed it makes the function a slight bit faster.
I actually have a number of other routines, CountSections and ParseSectionPOS being a couple of examples.
Unfortuately this routine is ansi/pchar based only. Although I don't think it would be difficult to move it to unicode. Maybe I've already done that...I'll have to check on that.
Note: This routine is 1 based in the ParseNum indexing.
function ParseSection(ParseLine: string; ParseNum: Integer; ParseSep: Char; QuotedStrChar:char = #0) : string;
var
wStart, wEnd : integer;
wIndex : integer;
wLen : integer;
wQuotedString : boolean;
begin
result := '';
wQuotedString := false;
if not (ParseLine = '') then
begin
wIndex := 1;
wStart := 1;
wEnd := 1;
wLen := Length(ParseLine);
while wEnd <= wLen do
begin
if (QuotedStrChar <> #0) and (ParseLine[wEnd] = QuotedStrChar) then
wQuotedString := not wQuotedString;
if not wQuotedString and (ParseLine[wEnd] = ParseSep) then
begin
if wIndex=ParseNum then
break
else
begin
inc(wIndex);
wStart := wEnd+1;
end;
end;
inc(wEnd);
end;
result := copy(ParseLine, wStart, wEnd-wStart);
if (length(result) > 0) and (QuotedStrChar <> #0) and (result[1] = QuotedStrChar) then
result := AnsiDequotedStr(result, QuotedStrChar);
end;
end; { ParseSection }
In your code, I think this is the only line that can be optimized:
Result := copy(Line, P+1, MaxInt)
If you calculate the new Length there, it might get a bit faster, but not the 10% you are looking for.
Your tokenizing algorithm seems pretty OK.
For optimizing it, I would run it through a profiler (like AQTime from AutomatedQA) with a representative subset of your production data. That will point you to the weakest spot.
The only RTL function that comes close is this one in the Classes unit:
procedure TStrings.SetDelimitedText(const Value: string);
It tokenizes, but uses both QuoteChar and Delimiter, but you only use a Delimiter.
It uses the SetString function in the System unit which is a pretty fast way to set the content of a string based on a PChar/PAnsiChar/PUnicodeChar and a length.
That might get you some improvement as well; on the other hand, Copy is really fast too.
I'm not the person always blaming the algorithm, but if I look at the first piece of source,
the problem is that for string N, you do the POS/posexes for string 1..n-1 again too.
This means for N items, you do sum (n, n-1,n-2...1) POSes (=+/- 0.5*N^2) , while only N are needed.
If you simply cache the position of the last found result, e.g. in a record that is passed by VAR parameter, you can gain a lot.
type
TLastPosition = record
elementnr : integer; // last tokennumber
elementpos: integer; // character index of last match
end;
and then something
if tokennum=(lastposition.elementnr+1) then
begin
newpos:=posex(delim,line,lastposition.elementpos);
end;
Unfortunately, I don't have the time now to write it out, but I hope you get the idea