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Use safe writes in Xoshiro NextBytes #127410

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EgorBo wants to merge 2 commits into from
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Use safe writes in Xoshiro NextBytes #127410

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a7d9fe6
Use safe writes in Xoshiro NextBytes
EgorBo Apr 24, 2026
5cb1c48
Merge branch 'main' into safe-span-random-xoshiro
EgorBo Apr 27, 2026
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16 changes: 8 additions & 8 deletions src/libraries/System.Private.CoreLib/src/System/Random.Xoshiro128StarStarImpl.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,6 @@
using System.Diagnostics;
using System.Numerics;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

namespace System
{
Expand Down Expand Up @@ -176,13 +175,15 @@ public override long NextInt64(long minValue, long maxValue)

public override void NextBytes(byte[] buffer) => NextBytes((Span<byte>)buffer);

public override unsafe void NextBytes(Span<byte> buffer)
public override void NextBytes(Span<byte> buffer)
{
uint s0 = _s0, s1 = _s1, s2 = _s2, s3 = _s3;

while (buffer.Length >= sizeof(uint))
{
MemoryMarshal.Write(buffer, BitOperations.RotateLeft(s1 * 5, 7) * 9);
uint next = BitOperations.RotateLeft(s1 * 5, 7) * 9;
bool success = BitConverter.TryWriteBytes(buffer, next);
Debug.Assert(success);

// Update PRNG state.
uint t = s1 << 9;
Expand All @@ -199,12 +200,11 @@ public override unsafe void NextBytes(Span<byte> buffer)
if (!buffer.IsEmpty)
{
uint next = BitOperations.RotateLeft(s1 * 5, 7) * 9;
byte* remainingBytes = (byte*)&next;
Debug.Assert(buffer.Length < sizeof(uint));
for (int i = 0; i < buffer.Length; i++)
{
buffer[i] = remainingBytes[i];
}
Span<byte> remainingBytes = [0, 0, 0, 0];
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bool success = BitConverter.TryWriteBytes(remainingBytes, next);
Debug.Assert(success);
remainingBytes.Slice(0, buffer.Length).CopyTo(buffer);

// Update PRNG state.
uint t = s1 << 9;
Expand Down
16 changes: 8 additions & 8 deletions src/libraries/System.Private.CoreLib/src/System/Random.Xoshiro256StarStarImpl.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,6 @@
using System.Diagnostics;
using System.Numerics;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

namespace System
{
Expand Down Expand Up @@ -133,13 +132,15 @@ public override long NextInt64(long minValue, long maxValue)

public override void NextBytes(byte[] buffer) => NextBytes((Span<byte>)buffer);

public override unsafe void NextBytes(Span<byte> buffer)
public override void NextBytes(Span<byte> buffer)
{
ulong s0 = _s0, s1 = _s1, s2 = _s2, s3 = _s3;

while (buffer.Length >= sizeof(ulong))
{
MemoryMarshal.Write(buffer, BitOperations.RotateLeft(s1 * 5, 7) * 9);
ulong next = BitOperations.RotateLeft(s1 * 5, 7) * 9;
bool success = BitConverter.TryWriteBytes(buffer, next);
Debug.Assert(success);

// Update PRNG state.
ulong t = s1 << 17;
Expand All @@ -156,12 +157,11 @@ public override unsafe void NextBytes(Span<byte> buffer)
if (!buffer.IsEmpty)
{
ulong next = BitOperations.RotateLeft(s1 * 5, 7) * 9;
byte* remainingBytes = (byte*)&next;
Debug.Assert(buffer.Length < sizeof(ulong));
for (int i = 0; i < buffer.Length; i++)
{
buffer[i] = remainingBytes[i];
}
Span<byte> remainingBytes = [0, 0, 0, 0, 0, 0, 0, 0];
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bool success = BitConverter.TryWriteBytes(remainingBytes, next);
Debug.Assert(success);
remainingBytes.Slice(0, buffer.Length).CopyTo(buffer);

// Update PRNG state.
ulong t = s1 << 17;
Expand Down
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