Delphi Make Dictionary Static and Dont initialize Array.

PrimeDelphi/solution_1/PrimePas.dpr

@@ -13,19 +13,20 @@ uses
   Math,
   Windows;
 
+var
+	MyDict : TDictionary<NativeInt, NativeInt>;
+
 type
+
 	TPrimeSieve = class
 	private
 		FSieveSize: NativeInt;
 		FSieveSize2: NativeInt;
 		FSieveSizeSqrt: NativeInt;
-		FBitArray: array of ByteBool; //ByteBool: 4644. WordBool: 4232. LongBool: 3673
-		FMyDict: TDictionary<NativeInt, NativeInt>;
+		FBitArray: array of ByteBool;
 
-		procedure InitializeBits;
 	public
 		constructor Create(Size: Integer);
-		destructor Destroy; override;
 
 		procedure RunSieve; // Calculate the primes up to the specified limit
 
@@ -48,82 +49,26 @@ begin
 	//The optimization here is that we only store bits for *odd* numbers.
 	// So FBitArray[3] is if 3 is prime
 	// and FBitArray[4] is if 5 is prime
-	//GetBit and SetBit do the work of "div 2"
 	SetLength(FBitArray, FSieveSize2);
-	InitializeBits;
-
-	FMyDict := TDictionary<NativeInt, NativeInt>.Create;
-
-	// Historical data for validating our results - the number of primes
-	// to be found under some limit, such as 168 primes under 1000
-	FMyDict.Add(       10, 4); //nobody noticed that 1 is wrong? [2, 3, 5, 7]
-	FMyDict.Add(      100, 25);
-	FMyDict.Add(     1000, 168);
-	FMyDict.Add(    10000, 1229);
-	FMyDict.Add(   100000, 9592);
-	FMyDict.Add(  1000000, 78498);
-	FMyDict.Add( 10000000, 664579);
-	FMyDict.Add(100000000, 5761455);
-end;
-
-destructor TPrimeSieve.Destroy;
-begin
-	FreeAndNil(FMyDict);
-
-	inherited;
 end;
 
 function TPrimeSieve.CountPrimes: Integer;
 var
-	count: NativeInt;
 	i: NativeInt;
 begin
-	count := 0;
+	Result := 0;
 	for i := 0 to High(FBitArray) do
-	begin
-		if FBitArray[i] then
-			Inc(count);
-	end;
-
-	Result := count;
+   	if (not FBitArray[i]) then Inc(Result);  // remember logic is reversed
 end;
 
 function TPrimeSieve.ValidateResults: Boolean;
 begin
-	if FMyDict.ContainsKey(FSieveSize) then
-		Result := FMyDict[FSieveSize] = Self.CountPrimes
+	if MyDict.ContainsKey(FSieveSize) then
+		Result := MyDict[FSieveSize] = Self.CountPrimes
 	else
 		Result := False;
 end;
 
-procedure TPrimeSieve.InitializeBits;
-var
-	i: NativeInt;
-	remaining: NativeInt;
-begin
-	remaining := Length(FBitArray);
-	i := 0;
-	while remaining >= 8 do
-	begin
-		FBitArray[i]   := True;
-		FBitArray[i+1] := True;
-		FBitArray[i+2] := True;
-		FBitArray[i+3] := True;
-		FBitArray[i+4] := True;
-		FBitArray[i+5] := True;
-		FBitArray[i+6] := True;
-		FBitArray[i+7] := True;
-		Inc(i, 8);
-		Dec(remaining, 8);
-	end;
-	while remaining > 0 do
-	begin
-		FBitArray[i] := True;
-		Inc(i);
-		Dec(remaining);
-	end;
-end;
-
 procedure TPrimeSieve.RunSieve;
 var
 	num: NativeInt;
@@ -136,9 +81,9 @@ begin
 	begin
 		r:=factor AND $1;
 		num:=factor SHR 1;
-		while num<FSieveSize2 do
+		while num<FSieveSizeSqrt do
 		begin
-			if FBitArray[num] then
+			if (not FBitArray[num]) then   // logic is reversed to avoid initializer
 			begin
 				factor := (num SHL 1) OR r;
 				Break;
@@ -150,7 +95,7 @@ begin
 		num := factor*3 SHR 1;
 		while num<=FSieveSize2 do
 		begin
-			FBitArray[num]:=False;
+			FBitArray[num]:=true;  // logic is reversed.
 			Inc(num,factor);
 		end;
 
@@ -173,7 +118,7 @@ begin
 	begin
 		if (num and $1 = $1) then
 		begin
-			if FBitArray[num div 2] then
+			if not FBitArray[num div 2] then
 			begin
 				if ShowResults then
 					Write(IntToStr(num) + ', ');
@@ -200,7 +145,7 @@ begin
 	passes := 0;
 
 	sieve := nil;
-	while TTimeSpan.Subtract(Now, dtStart).TotalSeconds < 10 do
+	while TTimeSpan.Subtract(Now, dtStart).TotalSeconds < 5 do
 	begin
 		if Assigned(sieve) then
 			sieve.Free;
@@ -215,6 +160,22 @@ begin
 		sieve.PrintResults(False, tD.TotalSeconds, passes);
 end;
 
+Procedure InitStaticDictionary;
+begin
+	MyDict := TDictionary<NativeInt, NativeInt>.Create;
+
+	// Historical data for validating our results - the number of primes
+	// to be found under some limit, such as 168 primes under 1000
+	MyDict.Add(       10, 4); //nobody noticed that 1 is wrong? [2, 3, 5, 7]
+	MyDict.Add(      100, 25);
+	MyDict.Add(     1000, 168);
+	MyDict.Add(    10000, 1229);
+	MyDict.Add(   100000, 9592);
+	MyDict.Add(  1000000, 78498);
+	MyDict.Add( 10000000, 664579);
+	MyDict.Add(100000000, 5761455);
+end;
+
 {
 	Intel Core i5-9400 @ 2.90 GHz
 	- 32-bit: 4,809 passes
@@ -233,9 +194,20 @@ end;
   - 64-bit: DEAD SLOW of some reason
   Further optimizations:
   - 32-bit: 8,600+ passes
+
+  Optimization of Kim's code by glenkleidon
+  - Made the History class static (as it is in the c++ because define as a const)
+  - The initializer for Delphi ByteBool by default sets to false
+    previous implementation initialized every value to true first,
+    but a better optimization is to simply reverse the logic - false = true/
+     true=false so there is no need to initialize the array.
+    Techically Delphi could have used a call to
+       FillChar(FBitArray[0],FSieveSize2,1);
+    but dynamic arrays MAY not be contiguous and therefore not safe.
 }
 begin
 	try
+    InitStaticDictionary;
 		Main;
 		WriteLn('Press enter to close...');
 		Readln;