RingBuffer, SpscRingBuffer and DelayLine throw an undocumented `OverflowException` for sizes above 2^30, and a failed `RingBuffer.Resize` corrupts the buffer

[matt-edmondson]

What's wrong

All three power-of-two buffers round their size up with the same NextPower2 helper (RingBuffer.cs ~L214, SpscRingBuffer.cs ~L202, DelayLine.cs ~L180). For any input above 2^30 the result wraps to int.MinValue, and new T[int.MinValue] throws OverflowException. The constructors only validate the lower bound, and their docs promise ArgumentOutOfRangeException for bad sizes.

• RingBuffer<T>(length) and Resize(length) with length > 2^30: NextPower2(length) overflows (~L139).
• SpscRingBuffer<T>(capacity) with capacity >= 2^30: NextPower2(capacity + 1) overflows (~L90). With int.MaxValue, the + 1 itself also wraps.
• DelayLine(maxDelaySamples) with maxDelaySamples >= 2^30: the same as SpscRingBuffer (~L80).

RingBuffer.Resize is worse. AllocateBuffer (~L134-144) assigns Length and Capacity before allocating. When the allocation throws, the old Buffer stays in place but Capacity is int.MinValue, so the index mask becomes int.MaxValue. Subsequent PushBack calls index past the end of the array.

Repro (verified on net10.0)

new RingBuffer<byte>((1 << 30) + 1);   // OverflowException
new SpscRingBuffer<byte>(1 << 30);     // OverflowException
new DelayLine(1 << 30);                // OverflowException

RingBuffer<int> r = new(4); r.PushBack(1); r.PushBack(2);
try { r.Resize((1 << 30) + 1); } catch (OverflowException) { }
r.PushBack(0); r.PushBack(1); /* ... */ // IndexOutOfRangeException within a few pushes

Suggested fix

• Validate the upper bound up front with ArgumentOutOfRangeException.ThrowIfGreaterThan, and document the limits:
  • RingBuffer: length ≤ 1 << 30.
  • SpscRingBuffer and DelayLine: capacity ≤ (1 << 30) - 1, because they need the extra slot.
• In RingBuffer.AllocateBuffer, compute and allocate the new array before assigning any field, so a failure leaves the buffer unchanged.

Acceptance criteria

• Oversized constructor and Resize calls throw ArgumentOutOfRangeException.
• After a rejected Resize, the buffer still holds its previous contents and PushBack still works.

Same family as the closed #73 (the Resample index overflow) and #50 (the lower-bound check).

[matt-edmondson]

Triage

• Category: Bug
• Priority: Low. It needs sizes above 2^30. The documented exception type is wrong, and a failed Resize leaves the buffer corrupt, which is worth fixing on principle, but real-world exposure is small.
• Area / suggested assignment: NextPower2 and the constructors in RingBuffer, SpscRingBuffer and DelayLine, plus RingBuffer.AllocateBuffer.
• Duplicates: none. It is the same family as Contiguous* containers can't grow past 2^30 elements: Grow doubles into an overflow and Add throws ArgumentException #90 (contiguous containers) and the closed RingBuffer.Resample throws IndexOutOfRangeException and loses the buffer's contents for ~46k+ elements (int overflow) #73 and RingBuffer<T> constructors don't validate length, unlike its sibling ring buffers #50.
• In progress: no open PR.

Suggested next step: add upper-bound checks with ArgumentOutOfRangeException.ThrowIfGreaterThan, and allocate the new array before assigning any fields in AllocateBuffer. Fixing it together with #90 keeps the overflow handling consistent.

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