• Type: Correctness / Indexing assumptions
• Severity: High
• Component: FFT R2X domain setup
• Location:
  • Src/FFT/AMReX_FFT_R2X.H:259
  • Src/FFT/AMReX_FFT_R2X.H:267
  • Src/FFT/AMReX_FFT_R2X.H:299

Problem

R2X stores m_dom_rx = m_dom_0 (original box), but several derived domains are built with smallEnd = 0 and mixed length(...)/bigEnd(...) expressions. If domain.sm\ allEnd() != 0, later setBig(...) operations can generate invalid or truncated boxes.

Impact

• Wrong internal layouts for non-zero-origin domains.
• Potential invalid boxes, copy failures, or incorrect FFT results.

Suggested patch

If non-zero-origin support is not implemented in R2X, fail fast with an explicit invariant check.

--- a/Src/FFT/AMReX_FFT_R2X.H
+++ b/Src/FFT/AMReX_FFT_R2X.H
@@   
     AMREX_ALWAYS_ASSERT((m_dom_0.numPts() > 1) && (m_info.batch_size == 1));
+    AMREX_ALWAYS_ASSERT_WITH_MESSAGE(
+        m_dom_0.smallEnd() == IntVect(AMREX_D_DECL(0,0,0)),
+        "FFT::R2X currently requires domain.smallEnd() == 0");

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