Name the pair layouts used by VQSort compare-exchanges

Author: LittlePyx

hwy/contrib/sort/shared-inl.h

@@ -165,6 +165,10 @@ static_assert(SortConstants::MaxBufBytes<2>(64) <= 1664, "Unexpectedly high");
 namespace hwy {
 namespace HWY_NAMESPACE {
 
+namespace detail {
+enum class PairLayout { kIndependent, kMirrored };
+}  // namespace detail
+
 // Default tag / vector width selector.
 #if HWY_TARGET == HWY_RVV
 // Use LMUL = 1/2; for SEW=64 this ends up emulated via VSETVLI.

hwy/contrib/sort/sorting_networks-inl.h

@@ -51,7 +51,7 @@ struct SharedTraits : public Base {
   HWY_INLINE Vec<D> SortPairsDistance2(D d, Vec<D> v) const {
     const Base* base = static_cast<const Base*>(this);
     Vec<D> swapped = base->SwapAdjacentPairs(d, v);
-    base->template Sort2<true>(d, v, swapped);
+    base->template Sort2<PairLayout::kMirrored>(d, v, swapped);
     return base->OddEvenPairs(d, swapped, v);
   }
 
@@ -60,7 +60,7 @@ struct SharedTraits : public Base {
   HWY_INLINE Vec<D> SortPairsReverse8(D d, Vec<D> v) const {
     const Base* base = static_cast<const Base*>(this);
     Vec<D> swapped = base->ReverseKeys8(d, v);
-    base->template Sort2<true>(d, v, swapped);
+    base->template Sort2<PairLayout::kMirrored>(d, v, swapped);
     return base->OddEvenQuads(d, swapped, v);
   }
 
@@ -70,7 +70,7 @@ struct SharedTraits : public Base {
     const Base* base = static_cast<const Base*>(this);
     static_assert(Constants::kMaxCols <= 16, "Need actual Reverse16");
     Vec<D> swapped = base->ReverseKeys(d, v);
-    base->template Sort2<true>(d, v, swapped);
+    base->template Sort2<PairLayout::kMirrored>(d, v, swapped);
     return ConcatUpperLower(d, swapped, v);  // 8 = half of the vector
   }
 };

hwy/contrib/sort/traits-inl.h

@@ -550,7 +550,7 @@ struct TraitsLane : public Base {
   // according to Base.
   // Corresponds to a conditional swap, which is one "node" of a sorting
   // network. Min/Max are cheaper than compare + blend at least for integers.
-  template <bool kMirror = false, class D>
+  template <PairLayout kLayout = PairLayout::kIndependent, class D>
   HWY_INLINE void Sort2(D d, Vec<D>& a, Vec<D>& b) const {
     const Base* base = static_cast<const Base*>(this);
 
@@ -559,7 +559,8 @@ struct TraitsLane : public Base {
     // and two blends, except for mirrored floats: selecting opposite inputs
     // on a tie there would duplicate one zero after the lanes are merged.
 #if HWY_AVX3 < HWY_TARGET && HWY_TARGET <= HWY_SSSE3
-    if (sizeof(TFromD<D>) == 8 && !(kMirror && IsFloat<TFromD<D>>())) {
+    if (sizeof(TFromD<D>) == 8 &&
+        !(kLayout == PairLayout::kMirrored && IsFloat<TFromD<D>>())) {
       const Mask<D> cmp = base->Compare(d, a, b);
       a = IfThenElse(cmp, a, b);
       b = IfThenElse(cmp, b, a_copy);
@@ -570,7 +571,7 @@ struct TraitsLane : public Base {
     // Some floating-point Min/Max instructions both choose the second operand
     // for equal zeros. Keep one of each input. Mirrored lanes already compare
     // the same pair in opposite orders before selecting one result per lane.
-    if constexpr (!kMirror && IsFloat<TFromD<D>>()) {
+    if constexpr (kLayout == PairLayout::kIndependent && IsFloat<TFromD<D>>()) {
       b = base->Last(d, b, a_copy);
     } else {
       b = base->Last(d, a_copy, b);
@@ -588,7 +589,7 @@ struct TraitsLane : public Base {
     const Vec<D> cmp = VecFromMask(d, base->Compare(d, v, swapped));
     return IfVecThenElse(DupOdd(cmp), swapped, v);
 #else
-    Sort2<true>(d, v, swapped);
+    Sort2<PairLayout::kMirrored>(d, v, swapped);
     return base->OddEvenKeys(swapped, v);
 #endif
   }
@@ -598,7 +599,7 @@ struct TraitsLane : public Base {
   HWY_INLINE Vec<D> SortPairsDistance1(D d, Vec<D> v) const {
     const Base* base = static_cast<const Base*>(this);
     Vec<D> swapped = base->ReverseKeys2(d, v);
-    Sort2<true>(d, v, swapped);
+    Sort2<PairLayout::kMirrored>(d, v, swapped);
     return base->OddEvenKeys(swapped, v);
   }
 
@@ -607,7 +608,7 @@ struct TraitsLane : public Base {
   HWY_INLINE Vec<D> SortPairsReverse4(D d, Vec<D> v) const {
     const Base* base = static_cast<const Base*>(this);
     Vec<D> swapped = base->ReverseKeys4(d, v);
-    Sort2<true>(d, v, swapped);
+    Sort2<PairLayout::kMirrored>(d, v, swapped);
     return base->OddEvenPairs(d, swapped, v);
   }
 
@@ -618,7 +619,7 @@ struct TraitsLane : public Base {
     Vec<D> swapped = base->SwapAdjacentQuads(d, v);
     // Only used in Merge16, so this will not be used on AVX2 (which only has 4
     // u64 lanes), so skip the above optimization for 64-bit AVX2.
-    Sort2<true>(d, v, swapped);
+    Sort2<PairLayout::kMirrored>(d, v, swapped);
     return base->OddEvenQuads(d, swapped, v);
   }
 };

hwy/contrib/sort/traits128-inl.h

@@ -494,7 +494,7 @@ struct Traits128 : public Base {
     return v;
   }
 
-  template <bool /*kMirror*/ = false, class D, HWY_IF_U64_D(D)>
+  template <PairLayout = PairLayout::kIndependent, class D, HWY_IF_U64_D(D)>
   HWY_INLINE void Sort2(D d, Vec<D>& a, Vec<D>& b) const {
     const Base* base = static_cast<const Base*>(this);