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Fasten string replace by avoiding lots of SetLength(..., Length(...)+1) calls. Maybe. Haven't actually tested it ;-).

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This commit is contained in:
rosenfield.albert
2008-08-14 20:23:53 +00:00
parent e0d847ed8a
commit 538cfde530
1 changed files with 60 additions and 42 deletions
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100
source/helpers.pas
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@ -1046,14 +1046,9 @@ end;
Create UTF-8 text file
}
function openfs(filename: String): TFileStream;
var
header: array[0..2] of Byte;
begin
Result := TFileStream.Create(filename, fmCreate);
header[0] := $EF;
header[1] := $BB;
header[2] := $BF;
Result.WriteBuffer(header, 3);
Result.WriteBuffer(sUTF8BOMString, 3);
end;
{***
@ -1350,6 +1345,50 @@ begin
end;
{***
Attempt to do string replacement faster than StringReplace and WideStringReplace.
}
function escChars(Text: WideString; Char1: WideChar; Char2: WideChar; Char3: WideChar; Char4: WideChar): WideString;
const
// Attempt to match whatever the CPU cache will hold.
block: Cardinal = 65536;
var
bstart, bend, matches, i: Cardinal;
// These could be bumped to uint64 if necessary.
len, respos: Cardinal;
begin
len := Length(Text);
Result := '';
bend := 0;
respos := 0;
repeat
bstart := bend + 1;
bend := bstart + block - 1;
if bend > len then bend := len;
matches := 0;
for i := bstart to bend do if
(Text[i] = Char1) or
(Text[i] = Char2) or
(Text[i] = Char3) or
(Text[i] = Char4)
then Inc(matches);
SetLength(Result, bend + 1 - bstart + matches + respos);
for i := bstart to bend do begin
if
(Text[i] = Char1) or
(Text[i] = Char2) or
(Text[i] = Char3) or
(Text[i] = Char4)
then begin
Inc(respos);
Result[respos] := '\';
end;
Inc(respos);
Result[respos] := Text[i];
end;
until bend = len;
end;
{***
Escape all kinds of characters:
@ -1365,49 +1404,28 @@ end;
}
function esc(Text: WideString; ProcessJokerChars: Boolean = false; sql_version: integer = 50000): WideString;
var
i,len : Integer;
c: WideChar;
c1, c2, c3, c4: WideChar;
begin
c1 := '''';
c2 := '\';
c3 := '%';
c4 := '_';
if (not ProcessJokerChars) or (sql_version = SQL_VERSION_ANSI) then begin
// Do not escape joker-chars which are used in a LIKE-clause
c4 := '''';
c3 := '''';
end;
if sql_version = SQL_VERSION_ANSI then begin
// Do a manual iteration + replacing of single quotes, which is much
// faster than StringReplace on text with a large amount of replacements
Result := '';
for i := 1 to Length(Text) do
begin
if Text[i] = #39 then
Result := Result + #39#39
else
Result := Result + Text[i];
c2 := '''';
end;
end
else begin
len := Length(Text);
Result := '';
for i := 1 to len do begin
c := Text[i];
if (c = '''') or (c = '\') then
Result := Result + '\';
Result := Result + c;
end;
end;
if ProcessJokerChars then
begin
// Escape joker-chars which are used in a LIKE-clause
if sql_version <> SQL_VERSION_ANSI then begin
Result := WideStringReplace(Result, '%', '\%', [rfReplaceAll]);
Result := WideStringReplace(Result, '_', '\_', [rfReplaceAll]);
end;
end
else
begin
Result := escChars(Text, c1, c2, c3, c4);
if not ProcessJokerChars then begin
// Add surrounding single quotes only for non-LIKE-values
// because in all cases we're using ProcessLIKEChars we
// need to add leading and/or trailing joker-chars by hand
// without being escaped
Result := #39 + Result + #39;
Result := WideChar(#39) + Result + WideChar(#39);
end;
end;