BUG: Fix LUT compile failures on MSVC and Highway debug builds

  Two portability issues in the transposed-load LUT path:

  - kTransposeLength evaluated to 0 when kInitTranspose is false
    (kRows < kTransposeBy), producing a zero-size array that MSVC
    rejects. Clamp it to 1 as an unused placeholder.

  - Lanes(du) is not constexpr in Highway debug builds, so it cannot
    initialize a constexpr size_t. Use the HWY_LANES(T) macro, which
    is a compile-time constant in all build modes.

Author: seiko2plus

npsr/lut-inl.h

@@ -44,13 +44,16 @@ class Lut {
   // Implementation details for transposition optimization
   static constexpr size_t kTransposeBy = HWY_LANES(T);
   static constexpr size_t kTransposeTail = kRows % kTransposeBy;
-  static constexpr size_t kTransposeLength = (kRows - kTransposeTail) * kCols;
-
   // Determine at compile-time if transposition optimization is viable
   static constexpr bool kInitTranspose = !HWY_HAVE_SCALABLE && (
     kRows / kTransposeBy > 0 && kCols % kTransposeBy == 0 &&
     (kTransposeBy == 2 || kTransposeBy == 4) // Currently supports 2x or 4x unrolling
   );
+  // When kInitTranspose is false kTransposeLength would be 0 (kRows < kTransposeBy),
+  // which would produce a zero-size array (MSVC forbid it) — use 1 as a placeholder instead.
+  static constexpr size_t kTransposeLength = kInitTranspose
+      ? (kRows - kTransposeTail) * kCols
+      : 1;
 
  /**
    * @brief Constructs the table from row arrays.
@@ -145,7 +148,7 @@ class Lut {
     using TU = TFromD<DU>;
     const DU du;
 
-    constexpr size_t kLanes = Lanes(du);
+    constexpr size_t kLanes = HWY_LANES(T);
 
     // Only use transposed load if vector lanes match the transpose blocking factor
     if constexpr (kLanes == kTransposeBy) {
@@ -237,7 +240,7 @@ class Lut {
     const D d;
 
 #if !HWY_HAVE_SCALABLE
-    constexpr size_t kLanes = Lanes(du);
+    constexpr size_t kLanes = HWY_LANES(T);
     // Strategy 1: Vector size equals table width (Single Table Lookup)
     if constexpr (kLanes == kCols) {
       const auto ind = IndicesFromVec(d, idx);