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gcarrenogcarreno
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Merge pull request #151 from georges-hatem/main
replace FormatFloat with own implementation
2 parents b2e58aa + 47c9b93 commit b6b4be6

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‎entries/ghatem-fpc/README.md‎

Lines changed: 28 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -247,3 +247,31 @@ Another trial with various hash functions, a simple modulus vs. a slightly more
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Can be tested with the HASHMULT build option
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Finally, it seems choosing a dictionary size that is a prime number is also recommended: shaves 1 second out of 20 on my PC.
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## v.6 (2024-05-04)
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As of the latest results executed by Paweld, there are two main bottlenecks throttling the entire implementation, according to CallGrind and KCacheGrind:
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- function ExtractLineData, 23% of total cost, of which 9% is due to `fpc_stackcheck`
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- the hash lookup function, at 40% of total cost
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Currently, the hash lookup is done on an array of records. Increasing the array size causes slowness, and reducing it causes further collisions.
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Will try to see how to reduce collisions (increase array size), all while minimizing the cost of cache misses.
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Edit:
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The goal is to both:
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- minimize collisions on the hashes (keys) by having a good hash function, but also increase the size of the keys storage
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- minimize the size of the array of packed records
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The idea:
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- the dictionary will no longer point to a PStationData pointer, but rather to an index between 0 and StationCount, where the record is stored in the array.
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- -> data about the same station will be stored at the same index for all threads' data-arrays
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- -> names will also be stored at that same index upon first encounter, and is common to all threads
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- no locking needs to occur when the key is already found, since there is no multiple-write occurring
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- the data-arrays are pre-allocated, and a atomic-counter will be incremented to know where the next element will be stored.
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Thinking again, this is likely similar to the approach mentioned by @synopse in one of his comments.
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For the ExtractLineData, three ideas to try implementing:
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- avoid using a function, to get rid of the cost of stack checking
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- reduce branching, I think it should be possible to go from 3 if-statements, to only 1
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- unroll the loop (although I had tried this in the past, did not show any improvements)

‎entries/ghatem-fpc/src/OneBRC-nosharedname.lpr‎

Lines changed: 23 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -151,12 +151,12 @@ function Ceiling (const ANumber: Double): Integer; inline;
151151
Result := Trunc(ANumber) + Ord(Frac(ANumber) > 0);
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end;
153153

154-
function RoundExDouble (const aTemp: Double): Double; inline;
154+
function RoundExInteger (const aTemp: Double): Integer; inline;
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var
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vTmp: Double;
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begin
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vTmp := aTemp * 10;
159-
Result := Ceiling (vTmp) / 10;
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Result := Ceiling (vTmp);
160160
end;
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//---------------------------------------------------
@@ -473,8 +473,24 @@ procedure TOneBRC.MergeAll;
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//---------------------------------------------------
475475

476+
function MyFormatInt (const aIn: SmallInt): AnsiString; inline;
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begin
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Result := IntToStr(aIn);
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Insert ('.', Result, Length(Result));
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if Result[1] = '.' then begin
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Insert ('0', Result, 1);
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exit;
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end;
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if (Result[1] = '-') and (Result[2] = '.') then
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Insert('0', Result, 2);
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end;
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//---------------------------------------------------
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476492
procedure TOneBRC.GenerateOutput;
477-
var vMin, vMean, vMax: Double;
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var vMean: Integer;
478494
vStream: TStringStream;
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I, N: Int64;
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vData: PStationData;
@@ -507,14 +523,12 @@ procedure TOneBRC.GenerateOutput;
507523
// debatable, and the whole output generation is < 0.3 seconds, so not exactly worth it
508524
vHash := crc32c(0, @vStations[i][1], Length (vStations[i]));
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FStationsDicts[0].TryGetValue(vHash, vData);
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vMin := vData^.Min/10;
511-
vMax := vData^.Max/10;
512-
vMean := RoundExDouble(vData^.Sum/vData^.Count/10);
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vMean := RoundExInteger(vData^.Sum/vData^.Count/10);
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514528
vStream.WriteString(
515-
vStations[i] + '=' + FormatFloat('0.0', vMin)
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+ '/' + FormatFloat('0.0', vMean)
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+ '/' + FormatFloat('0.0', vMax) + ', '
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vStations[i] + '=' + MyFormatInt(vData^.Min)
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+ '/' + MyFormatInt(vMean)
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+ '/' + MyFormatInt(vData^.Max) + ', '
518532
);
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Inc(I);
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end;
@@ -645,4 +659,3 @@ procedure TOneBRCApp.WriteHelp;
645659
end.
646660

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{$ENDREGION}
648-

‎entries/ghatem-fpc/src/OneBRC-smallrec.lpr‎

Lines changed: 23 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -154,12 +154,12 @@ function Ceiling (const ANumber: Double): Integer; inline;
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Result := Trunc(ANumber) + Ord(Frac(ANumber) > 0);
155155
end;
156156

157-
function RoundExDouble (const aTemp: Double): Double; inline;
157+
function RoundExInteger (const aTemp: Double): Integer; inline;
158158
var
159159
vTmp: Double;
160160
begin
161161
vTmp := aTemp * 10;
162-
Result := Ceiling (vTmp) / 10;
162+
Result := Ceiling (vTmp);
163163
end;
164164

165165
//---------------------------------------------------
@@ -487,8 +487,24 @@ procedure TOneBRC.MergeAll;
487487

488488
//---------------------------------------------------
489489

490+
function MyFormatInt (const aIn: SmallInt): AnsiString; inline;
491+
begin
492+
Result := IntToStr(aIn);
493+
Insert ('.', Result, Length(Result));
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495+
if Result[1] = '.' then begin
496+
Insert ('0', Result, 1);
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exit;
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end;
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if (Result[1] = '-') and (Result[2] = '.') then
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Insert('0', Result, 2);
502+
end;
503+
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//---------------------------------------------------
505+
490506
procedure TOneBRC.GenerateOutput;
491-
var vMin, vMean, vMax: Double;
507+
var vMean: Integer;
492508
vStream: TStringStream;
493509
I, N: Int64;
494510
vData: PStationData;
@@ -521,14 +537,12 @@ procedure TOneBRC.GenerateOutput;
521537
// debatable, and the whole output generation is < 0.3 seconds, so not exactly worth it
522538
vHash := crc32c(0, @vStations[i][1], Length (vStations[i]));
523539
FStationsDicts[0].TryGetValue(vHash, vData);
524-
vMin := vData^.Min/10;
525-
vMax := vData^.Max/10;
526-
vMean := RoundExDouble(vData^.Sum/vData^.Count/10);
540+
vMean := RoundExInteger(vData^.Sum/vData^.Count/10);
527541

528542
vStream.WriteString(
529-
vStations[i] + '=' + FormatFloat('0.0', vMin)
530-
+ '/' + FormatFloat('0.0', vMean)
531-
+ '/' + FormatFloat('0.0', vMax) + ', '
543+
vStations[i] + '=' + MyFormatInt(vData^.Min)
544+
+ '/' + MyFormatInt(vMean)
545+
+ '/' + MyFormatInt(vData^.Max) + ', '
532546
);
533547
Inc(I);
534548
end;
@@ -659,4 +673,3 @@ procedure TOneBRCApp.WriteHelp;
659673
end.
660674

661675
{$ENDREGION}
662-

‎entries/ghatem-fpc/src/OneBRC.lpr‎

Lines changed: 23 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -154,12 +154,12 @@ function Ceiling (const ANumber: Double): Integer; inline;
154154
Result := Trunc(ANumber) + Ord(Frac(ANumber) > 0);
155155
end;
156156

157-
function RoundExDouble (const aTemp: Double): Double; inline;
157+
function RoundExInteger (const aTemp: Double): Integer; inline;
158158
var
159159
vTmp: Double;
160160
begin
161161
vTmp := aTemp * 10;
162-
Result := Ceiling (vTmp) / 10;
162+
Result := Ceiling (vTmp);
163163
end;
164164

165165
//---------------------------------------------------
@@ -487,8 +487,24 @@ procedure TOneBRC.MergeAll;
487487

488488
//---------------------------------------------------
489489

490+
function MyFormatInt (const aIn: SmallInt): AnsiString; inline;
491+
begin
492+
Result := IntToStr(aIn);
493+
Insert ('.', Result, Length(Result));
494+
495+
if Result[1] = '.' then begin
496+
Insert ('0', Result, 1);
497+
exit;
498+
end;
499+
500+
if (Result[1] = '-') and (Result[2] = '.') then
501+
Insert('0', Result, 2);
502+
end;
503+
504+
//---------------------------------------------------
505+
490506
procedure TOneBRC.GenerateOutput;
491-
var vMin, vMean, vMax: Double;
507+
var vMean: Integer;
492508
vStream: TStringStream;
493509
I, N: Int64;
494510
vData: PStationData;
@@ -521,14 +537,12 @@ procedure TOneBRC.GenerateOutput;
521537
// debatable, and the whole output generation is < 0.3 seconds, so not exactly worth it
522538
vHash := crc32c(0, @vStations[i][1], Length (vStations[i]));
523539
FStationsDicts[0].TryGetValue(vHash, vData);
524-
vMin := vData^.Min/10;
525-
vMax := vData^.Max/10;
526-
vMean := RoundExDouble(vData^.Sum/vData^.Count/10);
540+
vMean := RoundExInteger(vData^.Sum/vData^.Count/10);
527541

528542
vStream.WriteString(
529-
vStations[i] + '=' + FormatFloat('0.0', vMin)
530-
+ '/' + FormatFloat('0.0', vMean)
531-
+ '/' + FormatFloat('0.0', vMax) + ', '
543+
vStations[i] + '=' + MyFormatInt(vData^.Min)
544+
+ '/' + MyFormatInt(vMean)
545+
+ '/' + MyFormatInt(vData^.Max) + ', '
532546
);
533547
Inc(I);
534548
end;
@@ -659,4 +673,3 @@ procedure TOneBRCApp.WriteHelp;
659673
end.
660674

661675
{$ENDREGION}
662-

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