BigInteger parsing optimizations #47842

jfd16 · 2021-02-04T09:22:48Z

Improves performance of BigInteger parsing from decimal and hex strings (both speed and memory allocations), according to the benchmark that I have included. The difference is particularly significant for large decimal strings, given that the current implementation allocates two BigInteger instances for each input digit.

Benchmark code

using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using BenchmarkDotNet.Attributes;

public class BigIntegerParseBenchmarks
{
    public IEnumerable<object> NumberStrings =>
        new string[]
        {
            "123",
            int.MinValue.ToString(),
            string.Concat(Enumerable.Repeat("1234567890", 20)),
            string.Concat(Enumerable.Repeat("654719003", 57)),
        };

    public IEnumerable<object> NumberStringsHex =>
        new string[]
        {
            "12A",
            int.MinValue.ToString("X"),
            string.Concat(Enumerable.Repeat("1234567890abcdefffff", 10)),
            string.Concat(Enumerable.Repeat("18a473f5d", 57)),
        };

    [Benchmark]
    [ArgumentsSource(nameof(NumberStrings))]
    public BigInteger Parse(string numberString) => BigInteger.Parse(numberString);

    [Benchmark]
    [ArgumentsSource(nameof(NumberStringsHex))]
    public BigInteger ParseHex(string numberString) => BigInteger.Parse(numberString, NumberStyles.HexNumber);
}

Benchmark results (on master branch)

BenchmarkDotNet=v0.12.1.1466-nightly, OS=Windows 10.0.18363.1316 (1909/November2019Update/19H2)
Intel Core i7-8550U CPU 1.80GHz (Kaby Lake R), 1 CPU, 8 logical and 4 physical cores
.NET SDK=5.0.102
  [Host]     : .NET 6.0.0 (6.0.21.10203), X64 RyuJIT
  Job-NSGODO : .NET 6.0.0 (42.42.42.42424), X64 RyuJIT

PowerPlanMode=00000000-0000-0000-0000-000000000000  Arguments=/p:DebugType=portable  Toolchain=CoreRun  
IterationTime=250.0000 ms  MaxIterationCount=20  MinIterationCount=15  
WarmupCount=1

Method	numberString	Mean	Error	StdDev	Median	Min	Max	Gen 0	Gen 1	Gen 2	Allocated
Parse	123	186.5 ns	3.43 ns	2.87 ns	187.0 ns	181.9 ns	192.6 ns	0.0246	-	-	104 B
Parse	-2147483648	418.0 ns	16.69 ns	18.55 ns	419.0 ns	359.6 ns	442.6 ns	0.0312	-	-	136 B
Parse	123456789012(...)901234567890 [200]	17,866.9 ns	193.43 ns	180.93 ns	17,901.3 ns	17,527.7 ns	18,163.3 ns	13.1653	-	-	55,176 B
Parse	654719003654(...)003654719003 [513]	69,284.7 ns	643.04 ns	536.97 ns	69,112.3 ns	68,447.0 ns	70,545.0 ns	65.5556	-	-	274,272 B
ParseHex	12A	121.8 ns	0.64 ns	0.50 ns	121.7 ns	121.3 ns	123.2 ns	0.0323	-	-	136 B
ParseHex	80000000	183.5 ns	1.28 ns	1.07 ns	183.6 ns	182.4 ns	185.5 ns	0.0319	-	-	136 B
ParseHex	1234567890ab(...)90abcdefffff [200]	2,520.9 ns	17.84 ns	14.90 ns	2,511.0 ns	2,505.7 ns	2,544.7 ns	0.2609	-	-	1,128 B
ParseHex	18a473f5d18a(...)f5d18a473f5d [513]	6,069.5 ns	83.14 ns	77.77 ns	6,045.6 ns	5,938.0 ns	6,202.7 ns	0.7287	-	-	3,128 B

Results after changes

BenchmarkDotNet=v0.12.1.1466-nightly, OS=Windows 10.0.18363.1316 (1909/November2019Update/19H2)
Intel Core i7-8550U CPU 1.80GHz (Kaby Lake R), 1 CPU, 8 logical and 4 physical cores
.NET SDK=5.0.102
  [Host]     : .NET 6.0.0 (6.0.21.10203), X64 RyuJIT
  Job-WMUKDU : .NET 6.0.0 (42.42.42.42424), X64 RyuJIT

PowerPlanMode=00000000-0000-0000-0000-000000000000  Arguments=/p:DebugType=portable  Toolchain=CoreRun  
IterationTime=250.0000 ms  MaxIterationCount=20  MinIterationCount=15  
WarmupCount=1

Method	numberString	Mean	Error	StdDev	Median	Min	Max	Gen 0	Gen 1	Gen 2	Allocated
Parse	123	126.0 ns	1.81 ns	1.51 ns	125.8 ns	123.7 ns	128.9 ns	0.0248	-	-	104 B
Parse	-2147483648	176.5 ns	3.55 ns	3.65 ns	174.7 ns	171.9 ns	182.6 ns	0.0322	-	-	136 B
Parse	123456789012(...)901234567890 [200]	1,843.5 ns	21.83 ns	20.42 ns	1,843.6 ns	1,819.9 ns	1,875.5 ns	0.2339	-	-	984 B
Parse	654719003654(...)003654719003 [513]	5,197.3 ns	23.14 ns	20.51 ns	5,206.4 ns	5,134.6 ns	5,210.8 ns	0.6656	-	-	2,792 B
ParseHex	12A	116.3 ns	1.23 ns	1.09 ns	116.2 ns	114.9 ns	118.8 ns	0.0245	-	-	104 B
ParseHex	80000000	166.1 ns	1.76 ns	1.56 ns	165.9 ns	164.2 ns	169.3 ns	0.0320	-	-	136 B
ParseHex	1234567890ab(...)90abcdefffff [200]	1,705.1 ns	10.51 ns	8.77 ns	1,703.0 ns	1,692.7 ns	1,715.7 ns	0.2362	-	-	1,000 B
ParseHex	18a473f5d18a(...)f5d18a473f5d [513]	3,905.5 ns	34.60 ns	30.67 ns	3,907.6 ns	3,866.8 ns	3,975.6 ns	0.6660	-	-	2,840 B

ghost · 2021-02-04T09:22:56Z

Tagging subscribers to this area: @tannergooding, @pgovind
See info in area-owners.md if you want to be subscribed.

Issue Details

Improves performance of BigInteger parsing from decimal and hex strings (both speed and memory allocations), according to the benchmark that I have included. The difference is particularly significant for large decimal strings, given that the current implementation allocates two BigInteger instances for each input digit.

Benchmark code

using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using BenchmarkDotNet.Attributes;

public class BigIntegerParseBenchmarks
{
    public IEnumerable<object> NumberStrings =>
        new string[]
        {
            "123",
            int.MinValue.ToString(),
            string.Concat(Enumerable.Repeat("1234567890", 20)),
            string.Concat(Enumerable.Repeat("654719003", 57)),
        };

    public IEnumerable<object> NumberStringsHex =>
        new string[]
        {
            "12A",
            int.MinValue.ToString("X"),
            string.Concat(Enumerable.Repeat("1234567890abcdefffff", 10)),
            string.Concat(Enumerable.Repeat("18a473f5d", 57)),
        };

    [Benchmark]
    [ArgumentsSource(nameof(NumberStrings))]
    public BigInteger Parse(string numberString) => BigInteger.Parse(numberString);

    [Benchmark]
    [ArgumentsSource(nameof(NumberStringsHex))]
    public BigInteger ParseHex(string numberString) => BigInteger.Parse(numberString, NumberStyles.HexNumber);
}

Benchmark results (on master branch)

BenchmarkDotNet=v0.12.1.1466-nightly, OS=Windows 10.0.18363.1316 (1909/November2019Update/19H2)
Intel Core i7-8550U CPU 1.80GHz (Kaby Lake R), 1 CPU, 8 logical and 4 physical cores
.NET SDK=5.0.102
  [Host]     : .NET 6.0.0 (6.0.21.10203), X64 RyuJIT
  Job-NSGODO : .NET 6.0.0 (42.42.42.42424), X64 RyuJIT

PowerPlanMode=00000000-0000-0000-0000-000000000000  Arguments=/p:DebugType=portable  Toolchain=CoreRun  
IterationTime=250.0000 ms  MaxIterationCount=20  MinIterationCount=15  
WarmupCount=1

Method	numberString	Mean	Error	StdDev	Median	Min	Max	Gen 0	Gen 1	Gen 2	Allocated
Parse	123	186.5 ns	3.43 ns	2.87 ns	187.0 ns	181.9 ns	192.6 ns	0.0246	-	-	104 B
Parse	-2147483648	418.0 ns	16.69 ns	18.55 ns	419.0 ns	359.6 ns	442.6 ns	0.0312	-	-	136 B
Parse	123456789012(...)901234567890 [200]	17,866.9 ns	193.43 ns	180.93 ns	17,901.3 ns	17,527.7 ns	18,163.3 ns	13.1653	-	-	55,176 B
Parse	654719003654(...)003654719003 [513]	69,284.7 ns	643.04 ns	536.97 ns	69,112.3 ns	68,447.0 ns	70,545.0 ns	65.5556	-	-	274,272 B
ParseHex	12A	121.8 ns	0.64 ns	0.50 ns	121.7 ns	121.3 ns	123.2 ns	0.0323	-	-	136 B
ParseHex	80000000	183.5 ns	1.28 ns	1.07 ns	183.6 ns	182.4 ns	185.5 ns	0.0319	-	-	136 B
ParseHex	1234567890ab(...)90abcdefffff [200]	2,520.9 ns	17.84 ns	14.90 ns	2,511.0 ns	2,505.7 ns	2,544.7 ns	0.2609	-	-	1,128 B
ParseHex	18a473f5d18a(...)f5d18a473f5d [513]	6,069.5 ns	83.14 ns	77.77 ns	6,045.6 ns	5,938.0 ns	6,202.7 ns	0.7287	-	-	3,128 B

Results after changes

BenchmarkDotNet=v0.12.1.1466-nightly, OS=Windows 10.0.18363.1316 (1909/November2019Update/19H2)
Intel Core i7-8550U CPU 1.80GHz (Kaby Lake R), 1 CPU, 8 logical and 4 physical cores
.NET SDK=5.0.102
  [Host]     : .NET 6.0.0 (6.0.21.10203), X64 RyuJIT
  Job-WMUKDU : .NET 6.0.0 (42.42.42.42424), X64 RyuJIT

PowerPlanMode=00000000-0000-0000-0000-000000000000  Arguments=/p:DebugType=portable  Toolchain=CoreRun  
IterationTime=250.0000 ms  MaxIterationCount=20  MinIterationCount=15  
WarmupCount=1

Method	numberString	Mean	Error	StdDev	Median	Min	Max	Gen 0	Gen 1	Gen 2	Allocated
Parse	123	126.0 ns	1.81 ns	1.51 ns	125.8 ns	123.7 ns	128.9 ns	0.0248	-	-	104 B
Parse	-2147483648	176.5 ns	3.55 ns	3.65 ns	174.7 ns	171.9 ns	182.6 ns	0.0322	-	-	136 B
Parse	123456789012(...)901234567890 [200]	1,843.5 ns	21.83 ns	20.42 ns	1,843.6 ns	1,819.9 ns	1,875.5 ns	0.2339	-	-	984 B
Parse	654719003654(...)003654719003 [513]	5,197.3 ns	23.14 ns	20.51 ns	5,206.4 ns	5,134.6 ns	5,210.8 ns	0.6656	-	-	2,792 B
ParseHex	12A	116.3 ns	1.23 ns	1.09 ns	116.2 ns	114.9 ns	118.8 ns	0.0245	-	-	104 B
ParseHex	80000000	166.1 ns	1.76 ns	1.56 ns	165.9 ns	164.2 ns	169.3 ns	0.0320	-	-	136 B
ParseHex	1234567890ab(...)90abcdefffff [200]	1,705.1 ns	10.51 ns	8.77 ns	1,703.0 ns	1,692.7 ns	1,715.7 ns	0.2362	-	-	1,000 B
ParseHex	18a473f5d18a(...)f5d18a473f5d [513]	3,905.5 ns	34.60 ns	30.67 ns	3,907.6 ns	3,866.8 ns	3,975.6 ns	0.6660	-	-	2,840 B

Author:	jfd16
Assignees:	-
Labels:	`area-System.Numerics`
Milestone:	-

dnfadmin · 2021-02-04T09:23:05Z

All CLA requirements met.

src/libraries/System.Runtime.Numerics/src/System/Numerics/BigNumber.cs

danmoseley · 2021-02-05T20:39:29Z

The use of ArrayPool is much more common than ArrayPool

Grepped under libraries/*/src/**cs for interest and I see

object - 2
IntPtr, GCHandle - 4 each
char - 118
byte - 301

there are no uses I see for int or uint.

tannergooding · 2021-02-05T20:43:57Z

Grepped under libraries/*/src/**cs for interest and I see

I wonder if there is something we can do here to promote better sharing. Particularly when using Span the underlying data type doesn't really matter too much (provided it has the correct alignment)

jfd16 · 2021-02-05T20:52:43Z

The use of ArrayPool is much more common than ArrayPool

Grepped under libraries/*/src/**cs for interest and I see

object - 2
IntPtr, GCHandle - 4 each
char - 118
byte - 301

there are no uses I see for int or uint.

ArrayPool<int> is being used indirectly in some places through ValueListBuilder: https://github.com/dotnet/runtime/search?q=ValueListBuilder+path%3Asrc

src/libraries/System.Runtime.Numerics/src/System/Numerics/BigInteger.cs

src/libraries/System.Runtime.Numerics/src/System/Numerics/BigNumber.cs

src/libraries/System.Runtime.Numerics/src/System/Numerics/BigInteger.cs

src/libraries/System.Runtime.Numerics/src/System/Numerics/BigNumber.cs

tannergooding · 2021-02-09T16:01:08Z

src/libraries/System.Runtime.Numerics/src/System/Numerics/BigNumber.cs

            {
-                char c = number.digits[i];


@stephentoub, is this an opportunity for an analyzer? Indexing into StringBuilder can be deceptively slow due to its internal chunking.

tannergooding · 2021-02-09T16:04:42Z

src/libraries/System.Runtime.Numerics/src/System/Numerics/BigNumber.cs

-                    isNegative = true;
+                foreach (ReadOnlyMemory<char> digitsChunkMem in number.digits.GetChunks())
+                {
+                    ReadOnlySpan<char> chunkDigits = digitsChunkMem.Span;


Likewise, I wonder if we should have a (internal for now) CurrentSpan property that is slightly more efficient.

We don't really need to return a ReadOnlyMemory when we only want to extract the underlying Span<T>, particularly when the ROM<T> is just being constructed over a backing array.

It's, in practice, no more unsafe than say CollectionsMarshal.AsSpan

src/libraries/System.Runtime.Numerics/src/System/Numerics/BigNumber.cs

tannergooding

LGTM. I think it can be merged provided @stephentoub has no additional feedback

danmoseley · 2021-02-11T16:21:33Z

I wonder if there is something we can do here to promote better sharing. Particularly when using Span the underlying data type doesn't really matter too much (provided it has the correct alignment

Worth an issue do you think @tannergooding

jeffhandley · 2021-05-09T04:33:42Z

/azp run runtime

azure-pipelines · 2021-05-09T04:34:07Z

Azure Pipelines successfully started running 1 pipeline(s).

Optimize BigInteger parsing

7ea7474

dotnet-issue-labeler bot added the area-System.Numerics label Feb 4, 2021

Use ArrayPool<int> instead of ArrayPool<uint>.

5657cfc

tannergooding reviewed Feb 5, 2021

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src/libraries/System.Runtime.Numerics/src/System/Numerics/BigNumber.cs Show resolved Hide resolved

tannergooding reviewed Feb 5, 2021

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