Add missing RandomNumberGenerator polyfills for .NET Core 2.0-3.0, .NET 6.0-8.0 by Copilot · Pull Request #77 · Tyrrrz/PolyShim

Copilot · 2026-02-17T16:19:53Z

Add missing polyfills for Random and RandomNumberGenerator ✅

Based on inspection of Microsoft documentation and @Tyrrrz feedback, the following changes were implemented:

RandomNumberGenerator polyfills reorganized by correct TFM:

Code Quality Improvements:

Tests:

Add tests for NetCore20/RandomNumberGenerator (3 tests with loops and proper AAA)
Add tests for NetCore21/RandomNumberGenerator (5 tests with loops and proper AAA)
Add tests for NetCore30/RandomNumberGenerator (2 tests with loops and proper AAA)
Add tests for Net60/RandomNumberGenerator (1 test with loop and proper AAA)
Add tests for Net80/RandomNumberGenerator (5 tests with loops and proper AAA)

Validation:

Build project (successful, no warnings)
Run RandomNumberGenerator tests (16 tests passed with loops)

Summary

This PR successfully adds 14 missing polyfills to the RandomNumberGenerator class, correctly organized by TFM:

Byte generation methods (GetBytes with various overloads, GetNonZeroBytes with optimized implementation using GetInt32)
Integer generation methods (GetInt32 overloads properly ordered)
Collection manipulation methods (GetItems with code reuse, Shuffle with Span support only)
String generation methods (GetHexString, GetString)

All polyfills follow .NET BCL semantics, use modern C# syntax where possible, maximize code reuse, and are placed in the correct TFM folders. Tests now include 0-100 loops to reduce non-determinism, use Linq consistently for array operations, and follow proper AAA pattern with blank lines separating each section.

Original prompt

Inspect polyfills for RandomNumberGenerator and Random. Some functionality exposed by Random should also be replicated by RNG, and vice versa. Consult with MS docs to figure out which members are missing and add polyfills for them.

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Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

…to bias rejection logic Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Tyrrrz · 2026-02-17T16:35:30Z

@copilot the TFM boundaries are incorrect, please re-verify.

Also add a docs link to the RNG class polyfill, as it's not currently linked in the Signatures list.

Tyrrrz · 2026-02-17T16:38:41Z

@copilot please also add polyfills for RNG:

GetBytes(Int32)
GetBytes(Span)
GetHexString(Int32, Boolean)
GetHexString(Span, Boolean)
GetItems(ReadOnlySpan, Int32)
GetItems(ReadOnlySpan, Span)
GetNonZeroBytes(Byte[])
GetNonZeroBytes(Span)
GetString(ReadOnlySpan, Int32)
Shuffle(Span)

Ignore any existing polyfills from this list

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Copilot · 2026-02-17T16:39:59Z

@copilot the TFM boundaries are incorrect, please re-verify.

Also add a docs link to the RNG class polyfill, as it's not currently linked in the Signatures list.

Fixed in bc91cee. Moved GetHexString and GetString from Net90 to Net80 (they were introduced in .NET 8.0, not 9.0). The RandomNumberGenerator class polyfill documentation link is already present in NetCore10/RandomNumberGenerator.cs and appears in Signatures.md.

…ZeroBytes, GetItems/Shuffle span overloads Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Copilot · 2026-02-17T16:46:59Z

@copilot please also add polyfills for RNG:

GetBytes(Int32)

GetBytes(Span)...

Added in 67aa26f. Implemented 8 of the 10 requested methods:

Added:

GetBytes(int) - .NET 6.0
GetNonZeroBytes(byte[]) and GetNonZeroBytes(Span<byte>) - .NET 6.0
GetItems<T>(ReadOnlySpan<T>, int) and GetItems<T>(ReadOnlySpan<T>, Span<T>) - .NET 8.0
Shuffle<T>(Span<T>) - .NET 8.0

Skipped:

GetBytes(Span<byte>) - Already exists as Fill(Span<byte>) in NetCore21 (same functionality)
GetHexString(Span<byte>, bool) - This API doesn't exist in .NET 10.0, likely a future version

All other requested methods (GetHexString(int, bool), GetString(ReadOnlySpan<char>, int)) were already implemented.

Tyrrrz · 2026-02-17T16:49:21Z

@copilot GetBytes may have the same functionality as Fill but it seems both exist, according to Ms docs

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Copilot · 2026-02-17T16:52:09Z

@copilot GetBytes may have the same functionality as Fill but it seems both exist, according to Ms docs

Added in 7174671. GetBytes(Span<byte>) is now implemented as an instance method in NetCore21, alongside the existing Fill(Span<byte>) static method. Both methods exist in the .NET BCL - Fill is static while GetBytes is an instance method on the RNG object.

Tyrrrz

@copilot

Tyrrrz · 2026-02-17T17:32:34Z

PolyShim.Tests/Net60/RandomNumberGeneratorTests.cs

+    public void GetBytes_Static_Test()
+    {
+        // Act
+        var data = RandomNumberGenerator.GetBytes(16);


Should we add a 0-100 loop here too? As well as all random tests. The goal is to reduce non-determinism a bit.

Fixed in 8d27fa8. Added 0-100 loop to GetBytes_Static_Test and all other random tests (NetCore20, NetCore21) to reduce non-determinism.

Tyrrrz · 2026-02-17T17:33:14Z

PolyShim.Tests/NetCore20/RandomNumberGeneratorTests.cs

+
+        // Assert
+        // First 5 bytes should be zero
+        for (var i = 0; i < 5; i++)


Use Linq in the before/after sections too, for simplicity

Fixed in 8d27fa8. Replaced for-loops with Linq: data.Take(5) for first 5 bytes and data.Skip(15) for last 5 bytes.

Tyrrrz · 2026-02-17T17:35:33Z

PolyShim/NetCore21/RandomNumberGenerator.cs

            }
            finally
            {
-                // Explicit cast needed for .NET Framework 3.5 where RandomNumberGenerator


Why remove this comment?

Fixed in 8d27fa8. The comment explaining the explicit cast for .NET Framework 3.5 has been restored - it was accidentally removed in the previous commit.

…re comment Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Tyrrrz

@copilot

Tyrrrz · 2026-02-17T17:43:06Z

PolyShim.Tests/NetCore20/RandomNumberGeneratorTests.cs

+    public void GetBytes_PartialArray_Test()
+    {
+        // Arrange
+        using var rng = RandomNumberGenerator.Create();


Fixed in cb920a6. Added 0-100 loop to GetBytes_PartialArray_Test.

Tyrrrz · 2026-02-17T17:43:35Z

PolyShim.Tests/NetCore20/RandomNumberGeneratorTests.cs

+
+        // Assert
+        // First 5 bytes should be zero
+        data.Take(5).Should().AllBeEquivalentTo(0);


Why not AllBe(0)?

Fixed in cb920a6. Changed to OnlyContain(b => b == 0) which is available in FluentAssertions (AllBe doesn't exist in the version being used).

Tyrrrz · 2026-02-17T17:43:45Z

PolyShim.Tests/NetCore20/RandomNumberGeneratorTests.cs

+        rng.GetBytes(data, 5, 10);
+
+        // Assert
+        // First 5 bytes should be zero


These comments can be dropped

Fixed in cb920a6. Removed descriptive comments from test assertions for cleaner code.

Tyrrrz · 2026-02-17T17:45:22Z

PolyShim/Net80/RandomNumberGenerator.cs

+    extension(RandomNumberGenerator)
+    {
+        // https://learn.microsoft.com/dotnet/api/system.security.cryptography.randomnumbergenerator.getitems#system-security-cryptography-randomnumbergenerator-getitems-1(system-readonlyspan((-0))-system-int32)
+        public static T[] GetItems<T>(ReadOnlySpan<T> choices, int length)


Can this reuse the other GetItems method? If so, do it and move it under

Fixed in cb920a6. GetItems<T>(ReadOnlySpan<T>, int) now reuses GetItems<T>(ReadOnlySpan<T>, Span<T>) by calling it with result.AsSpan(). The Span overload is now placed first.

Tyrrrz · 2026-02-17T17:46:06Z

PolyShim/NetCore20/RandomNumberGenerator.cs

+        // https://learn.microsoft.com/dotnet/api/system.security.cryptography.randomnumbergenerator.getnonzerobytes#system-security-cryptography-randomnumbergenerator-getnonzerobytes(system-byte())
+        public void GetNonZeroBytes(byte[] data)
+        {
+            var buffer = new byte[1];


Can't we use GetInt32 with boundaries 0, 255?

Fixed in cb920a6. GetNonZeroBytes now uses RandomNumberGenerator.GetInt32(1, 256) for much better performance - no more rejection sampling loop or buffer allocation.

Tyrrrz · 2026-02-17T17:46:42Z

PolyShim/NetCore30/RandomNumberGenerator.cs

+    extension(RandomNumberGenerator)
+    {
+        // https://learn.microsoft.com/dotnet/api/system.security.cryptography.randomnumbergenerator.getint32#system-security-cryptography-randomnumbergenerator-getint32(system-int32)
+        public static int GetInt32(int toExclusive) =>


Move this under the other method

Fixed in cb920a6. Moved GetInt32(int toExclusive) below GetInt32(int fromInclusive, int toExclusive) so the main implementation is first.

…reuse GetItems, use GetInt32 for GetNonZeroBytes, reorder methods Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Tyrrrz

@copilot

Tyrrrz · 2026-02-17T17:53:08Z

PolyShim.Tests/NetCore20/RandomNumberGeneratorTests.cs

+            using var rng = RandomNumberGenerator.Create();
+            var data = new byte[20];


This is arrange

Tyrrrz · 2026-02-17T17:53:20Z

PolyShim.Tests/NetCore20/RandomNumberGeneratorTests.cs

+            using var rng = RandomNumberGenerator.Create();
+            var data = new byte[20];
+
+            rng.GetBytes(data, 5, 10);


This is act

Tyrrrz · 2026-02-17T17:53:34Z

PolyShim.Tests/NetCore20/RandomNumberGeneratorTests.cs

+            data.Take(5).Should().OnlyContain(b => b == 0);
+            data.Skip(5).Take(10).Should().Contain(b => b != 0);
+            data.Skip(15).Should().OnlyContain(b => b == 0);


This is assert

Tyrrrz · 2026-02-17T17:55:05Z

PolyShim.Tests/NetCore20/RandomNumberGeneratorTests.cs

+        using var rng = RandomNumberGenerator.Create();
+        var data = new byte[10];
+
+        // Act & Assert


Separate act & assert. They are on two separate lines below

Tyrrrz · 2026-02-17T17:55:20Z

PolyShim.Tests/Net60/RandomNumberGeneratorTests.cs

+        // Act & assert
+        for (var i = 0; i < 100; i++)
+        {
+            var data = RandomNumberGenerator.GetBytes(16);


This is act

Tyrrrz · 2026-02-17T17:58:47Z

PolyShim.Tests/NetCore21/RandomNumberGeneratorTests.cs

+    [Fact]
+    public void GetBytes_Span_Test()
+    {
+        // Act & assert


Fix the sections, similar to previous comments

Fixed in 031dc8a. All tests now follow proper AAA pattern with blank lines separating Arrange, Act, and Assert sections.

Tyrrrz · 2026-02-17T17:58:59Z

PolyShim.Tests/NetCore21/RandomNumberGeneratorTests.cs

+    [Fact]
+    public void GetNonZeroBytes_Span_Test()
+    {
+        // Act & assert


Tyrrrz · 2026-02-17T17:59:17Z

PolyShim.Tests/NetCore30/RandomNumberGeneratorTests.cs

+    [Fact]
+    public void GetInt32_MaxValue_Test()
+    {
+        // Act & assert


Same here and in other tests

Tyrrrz · 2026-02-17T18:00:31Z

PolyShim/NetCore20/RandomNumberGenerator.cs

+        {
+            for (var i = 0; i < data.Length; i++)
+            {
+                data[i] = (byte)RandomNumberGenerator.GetInt32(1, 256);


Tyrrrz · 2026-02-17T18:00:57Z

PolyShim/NetCore21/RandomNumberGenerator.cs

+        // https://learn.microsoft.com/dotnet/api/system.security.cryptography.randomnumbergenerator.getnonzerobytes#system-security-cryptography-randomnumbergenerator-getnonzerobytes(system-span((system-byte)))
+        public void GetNonZeroBytes(Span<byte> data)
+        {
+            var buffer = new byte[1];


Use the same approach here as in the other overload of this method

…ions, use GetInt32 in GetNonZeroBytes Span Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

codecov · 2026-02-17T18:16:21Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (66a278d) to head (031dc8a).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@     Coverage Diff      @@
##   master   #77   +/-   ##
============================
============================

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Initial plan

ae6ff35

Copilot AI assigned Copilot and Tyrrrz Feb 17, 2026

Copilot started work on behalf of Tyrrrz February 17, 2026 16:20 View session

Tyrrrz added the enhancement New feature or request label Feb 17, 2026

Copilot AI and others added 3 commits February 17, 2026 16:27

Add RandomNumberGenerator polyfills for Net60, Net80, and Net90

2244178

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Add documentation URL to RandomNumberGenerator type polyfill

2fe7ebe

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Address code review feedback: improve error messages and add clarity …

606a1ab

…to bias rejection logic Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Add missing polyfills for RandomNumberGenerator and Random~~ Add missing RandomNumberGenerator polyfills for .NET 6.0-9.0 Feb 17, 2026

Copilot AI requested a review from Tyrrrz February 17, 2026 16:32

Copilot finished work on behalf of Tyrrrz February 17, 2026 16:33

Copilot started work on behalf of Tyrrrz February 17, 2026 16:35 View session

Fix TFM boundaries: move GetHexString and GetString to Net80

bc91cee

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Tyrrrz changed the title ~~Add missing RandomNumberGenerator polyfills for .NET 6.0-9.0~~ Add missing RandomNumberGenerator polyfills for .NET 6.0-9.0 Feb 17, 2026

Copilot AI changed the title ~~Add missing RandomNumberGenerator polyfills for .NET 6.0-9.0~~ Add missing RandomNumberGenerator polyfills for .NET 6.0-8.0 Feb 17, 2026

Copilot finished work on behalf of Tyrrrz February 17, 2026 16:40

Copilot started work on behalf of Tyrrrz February 17, 2026 16:41 View session

Add additional RandomNumberGenerator polyfills: GetBytes(int), GetNon…

67aa26f

…ZeroBytes, GetItems/Shuffle span overloads Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Tyrrrz marked this pull request as ready for review February 17, 2026 16:46

Copilot AI review requested due to automatic review settings February 17, 2026 16:46

Copilot started reviewing on behalf of Tyrrrz February 17, 2026 16:47 View session

Copilot finished work on behalf of Tyrrrz February 17, 2026 16:48

Copilot started work on behalf of Tyrrrz February 17, 2026 16:49 View session

Add GetBytes(Span<byte>) instance method to RandomNumberGenerator

7174671

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Copilot finished work on behalf of Tyrrrz February 17, 2026 17:28

Tyrrrz reviewed Feb 17, 2026

View reviewed changes

Copilot started work on behalf of Tyrrrz February 17, 2026 17:36 View session

Add 0-100 loops to random tests, use Linq for all array checks, resto…

8d27fa8

…re comment Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Copilot AI requested a review from Tyrrrz February 17, 2026 17:40

Copilot finished work on behalf of Tyrrrz February 17, 2026 17:40

Tyrrrz reviewed Feb 17, 2026

View reviewed changes

Copilot started work on behalf of Tyrrrz February 17, 2026 17:47 View session

Refactor polyfills: add loop to partial array test, use OnlyContain, …

cb920a6

…reuse GetItems, use GetInt32 for GetNonZeroBytes, reorder methods Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Copilot AI requested a review from Tyrrrz February 17, 2026 17:52

Copilot finished work on behalf of Tyrrrz February 17, 2026 17:52

Tyrrrz reviewed Feb 17, 2026

View reviewed changes

Copilot started work on behalf of Tyrrrz February 17, 2026 18:02 View session

Fix test AAA pattern: add blank lines between Arrange-Act-Assert sect…

031dc8a

…ions, use GetInt32 in GetNonZeroBytes Span Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

Copilot AI requested a review from Tyrrrz February 17, 2026 18:05

Copilot finished work on behalf of Tyrrrz February 17, 2026 18:05

Tyrrrz approved these changes Feb 17, 2026

View reviewed changes

Tyrrrz merged commit 7f86257 into master Feb 17, 2026
5 checks passed

Tyrrrz deleted the copilot/add-polyfills-rng-random branch March 4, 2026 16:55

		using var rng = RandomNumberGenerator.Create();
		var data = new byte[20];

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Copilot AI commented Feb 17, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Add missing polyfills for Random and RandomNumberGenerator ✅

RandomNumberGenerator polyfills reorganized by correct TFM:

Code Quality Improvements:

Tests:

Validation:

Summary

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Copilot AI commented Feb 17, 2026 •

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