Walkthrough

Replaces dynamic list with a pre-sized string[] for QR lines, adds a HAS_SPAN-guarded fast path using stack-allocated Span<char> when conditions allow, and updates the fallback to reuse a StringBuilder per line while computing capacities upfront and early-returning from the span path. (50 words)

Changes

Sequence Diagram(s)

sequenceDiagram
  autonumber
  participant Caller
  participant ASCIIQRCode as ASCIIQRCode.Generate
  participant SpanPath as HAS_SPAN Fast Path
  participant Builder as StringBuilder Fallback

  Caller->>ASCIIQRCode: Generate ASCII QR lines
  ASCIIQRCode->>ASCIIQRCode: compute sideLength & lineCapacity
  alt HAS_SPAN enabled && token lengths equal && small capacity
    ASCIIQRCode->>SpanPath: stackalloc Span<char>, fill each line directly
    SpanPath-->>ASCIIQRCode: populated string[] lines
    ASCIIQRCode-->>Caller: return string[] lines
  else Fallback
    ASCIIQRCode->>Builder: reuse/reset builder per line, append blocks
    Builder-->>ASCIIQRCode: write resulting string into pre-sized array
    ASCIIQRCode-->>Caller: return string[] lines
  end

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Suggested reviewers

• gfoidl

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QRCoder/ASCIIQRCode.cs (1)

71-74: Cache spans outside the hot loop

AsSpan() gets re-evaluated for every module even though the underlying strings never change. Caching var darkSpan = darkColorString.AsSpan(); / var whiteSpan = whiteSpaceString.AsSpan(); once before the loops lets you reuse them in the inner loop and avoids repeated method calls in this perf-sensitive path.

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Review profile: CHILL

Plan: Pro

QRCoder/ASCIIQRCode.cs (1)

59-81: Verify the lineCapacity < 510 threshold.

The 510 limit leaves a 2-char safety buffer in the 512-char stackalloc, but this might unnecessarily exclude cases where lineCapacity is 510-512. Unless there's a specific reason for this buffer, consider using <= 512 to maximize the fast path coverage.

If the 2-char buffer is intentional, adding a brief comment explaining why would improve maintainability:

+        // Limit to 510 to leave buffer space for safety/alignment
         if (darkColorString.Length == whiteSpaceString.Length && lineCapacity < 510)

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Review profile: CHILL

Plan: Pro