contrib/sort: enable f16/f64 sorting on no native FP

CMakeLists.txt

@@ -235,6 +235,7 @@ list(APPEND HWY_CONTRIB_SOURCES
     hwy/contrib/sort/sorting_networks-inl.h
     hwy/contrib/sort/traits-inl.h
     hwy/contrib/sort/traits128-inl.h
+    hwy/contrib/sort/order-emulate-inl.h
     hwy/contrib/sort/vqsort-inl.h
     hwy/contrib/sort/vqsort.cc
     hwy/contrib/sort/vqsort.h

hwy/contrib/sort/BUILD

@@ -115,6 +115,7 @@ VQSORT_TEXTUAL_HDRS = [
     "sorting_networks-inl.h",
     "traits-inl.h",
     "traits128-inl.h",
+    "order-emulate-inl.h",
     "vqsort-inl.h",
     # Placeholder for internal instrumentation. Do not remove.
 ]

hwy/contrib/sort/order-emulate-inl.h

@@ -0,0 +1,225 @@
+// Emulated floating-point total order
+//
+// This implementation sorts floating-point values by reinterpreting them as
+// unsigned integer bit patterns instead of using the FPU. It does not depend on
+// the floating-point control register, so there is no flush-to-zero handling.
+//
+// NaNs are already replaced by ±Inf before calling this code, so no special
+// handling is needed here.
+// Because ordering is emulated, we guarantee a stable rule for zeros: -0.0
+// always comes before +0.0.
+//
+// SPDX-License-Identifier: BSD-3-Clause
+#if defined(HIGHWAY_HWY_CONTRIB_SORT_ORDER_EMULATE_TOGGLE) == \
+    defined(HWY_TARGET_TOGGLE)
+#ifdef HIGHWAY_HWY_CONTRIB_SORT_ORDER_EMULATE_TOGGLE
+#undef HIGHWAY_HWY_CONTRIB_SORT_ORDER_EMULATE_TOGGLE
+#else
+#define HIGHWAY_HWY_CONTRIB_SORT_ORDER_EMULATE_TOGGLE
+#endif
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "hwy/contrib/sort/order.h"       // SortDescending
+#include "hwy/highway.h"
+
+HWY_BEFORE_NAMESPACE();
+namespace hwy {
+namespace HWY_NAMESPACE {
+namespace detail {
+
+
+template <class VU, class D = DFromV<VU>, class DI = RebindToSigned<D>>
+HWY_API Vec<DI> LtBinKey(VU a) {
+  using TI = TFromD<DI>;
+  using VI = Vec<DI>;
+  const DI di;
+  const VI neg_flip = Set(di, TI(SignMask<TI>() - 1));
+  return Xor(BitCast(di, a), IfNegativeThenElseZero(BitCast(di, a), neg_flip));
+}
+
+template <class VU, class D = DFromV<VU>, class M = MFromD<D>, HWY_IF_UNSIGNED_D(D)>
+HWY_API M LtBin(VU a, VU b) {
+  return RebindMask(D{}, Lt(LtBinKey(a), LtBinKey(b)));
+}
+
+template <class Base, class Order_>
+struct OrderEmulate : public Base {
+  using T = typename Base::LaneType;
+  using TF = typename Base::KeyType;
+
+  HWY_INLINE bool Equal1(const T* a, const T* b) const {
+    return *a == *b;
+  }
+
+  template <class D>
+  HWY_INLINE Mask<D> EqualKeys(D, Vec<D> a, Vec<D> b) const {
+    return Eq(a, b); // Bitwise equality, -0 != +0, +-NaN is equal to itself
+  }
+
+  template <class D>
+  HWY_INLINE Mask<D> NotEqualKeys(D, Vec<D> a, Vec<D> b) const {
+    return Ne(a, b); // bitwise inequality, -0 != +0, +-NaN is equal to itself
+  }
+
+  HWY_INLINE bool Compare1(const T* a_, const T* b_) const {
+    const T a = *a_;
+    const T b = *b_;
+    // specialized less than, -0.0 < +0.0, and NaNs are not ordered
+    using TI = MakeSigned<T>;
+    constexpr int kMSB = 8 * sizeof(T) - 1;
+    constexpr T neg_flip = T((T(1) << kMSB) - 1); 
+    const T a_neg = 0 - (a >> kMSB);
+    const T b_neg = 0 - (b >> kMSB);
+    // Signed-domain keys (xor 0x7FFF.. only for negatives)
+    const T sa = a ^ (a_neg & neg_flip);
+    const T sb = b ^ (b_neg & neg_flip);
+    return static_cast<TI>(sa) < static_cast<TI>(sb);
+  }
+  template <class D>
+  HWY_INLINE Mask<D> Compare(D, Vec<D> a, Vec<D> b) const {
+    // specialized less than, -0.0 < +0.0, and NaNs are not ordered
+    return LtBin(a, b);
+  }
+
+  // Two halves of Sort2, used in ScanMinMax.
+  template <class D>
+  HWY_INLINE Vec<D> First(D /* tag */, const Vec<D> a, const Vec<D> b) const {
+    return IfThenElse(LtBin(a, b), a, b);
+  }
+
+  template <class D>
+  HWY_INLINE Vec<D> Last(D /* tag */, const Vec<D> a, const Vec<D> b) const {
+    return IfThenElse(LtBin(a, b), b, a);
+  }
+
+  template <class D>
+  HWY_INLINE Vec<D> FirstOfLanes(D d, Vec<D> v,
+                                 T* HWY_RESTRICT /* buf */) const {
+    const RebindToSigned<D> di;
+    using VI = Vec<decltype(di)>;
+    VI key = LtBinKey(v);
+    VI min = MinOfLanes(di, key);
+    Mask<D> m = RebindMask(d, Eq(min, key));
+    return MaxOfLanes(d, IfThenElseZero(m, v));
+  }
+
+  template <class D>
+  HWY_INLINE Vec<D> LastOfLanes(D d, Vec<D> v,
+                                T* HWY_RESTRICT /* buf */) const {
+    const RebindToSigned<D> di;
+    using VI = Vec<decltype(di)>;
+    VI key = LtBinKey(v);
+    VI max = MaxOfLanes(di, key);
+    Mask<D> m = RebindMask(d, Eq(max, key));
+    return MaxOfLanes(d, IfThenElseZero(m, v));
+  }
+
+  template <class D>
+  HWY_INLINE Vec<D> FirstValue(D d) const {
+    return Set(d, BitCastScalar<T>(NegativeInfOrLowestValue<TF>()));
+  }
+
+  template <class D>
+  HWY_INLINE Vec<D> LastValue(D d) const {
+    return Set(d, BitCastScalar<T>(PositiveInfOrHighestValue<TF>()));
+  }
+
+  // Returns the next distinct smaller value unless already -inf.
+  template <class D, class V = Vec<D>>
+  HWY_INLINE V PrevValue(D, V v) const {
+    return NextSortValueBits<true>(v);
+  }
+
+  // Next representable value in total order by ±1 ULP, saturating at ±Inf.
+  //   IsDown = false → next larger
+  //   IsDown = true  → next smaller
+  template <bool IsDown, class V>
+  HWY_INLINE V NextSortValueBits(V u) const {
+    const DFromV<V> d;
+    using M = Mask<decltype(d)>;
+    constexpr T kSignBit = SignMask<T>();
+    constexpr T kBoundaryUp = SignMask<T>() - 1;
+    const V sign_bit = Set(d, kSignBit);
+    const V all1 = Set(d, T(~T(0)));
+    const V one = Set(d, T(1));
+    // Detect saturation at ±Inf
+    const M is_target_inf = Eq(u, IsDown ? FirstValue(d) : LastValue(d));
+    // Transform to monotonic space: flip sign for positives, invert for negatives
+    const M is_neg = TestBit(u, sign_bit);
+    const V key = Xor(u, IfThenElse(is_neg, all1, sign_bit));
+    // Boundary detection: +0/-0 swap needs a step of 2 instead of 1
+    const V boundary = Set(d, IsDown ? kSignBit : kBoundaryUp);
+    const M at_boundary = Eq(key, boundary);
+    // Step size: normally 1, but 2 at zero-boundary
+    const V step = Add(one, IfThenElseZero(at_boundary, one));
+    // Apply increment/decrement unless already at ±Inf
+    const V key2 = IfThenElse(is_target_inf, key,
+                              IsDown ? Sub(key, step) : Add(key, step));
+    // Transform back from monotonic space
+    const M neg_out = Lt(key2, sign_bit);
+    return Xor(key2, IfThenElse(neg_out, all1, sign_bit));
+  }
+};
+
+template <class Base>
+struct OrderEmulate<Base, SortDescending> : public OrderEmulate<Base, SortAscending> {
+  using T = typename Base::LaneType;
+
+  HWY_INLINE const OrderEmulate<Base, SortAscending>& AscBase() const {
+    return *this;
+  }
+
+  HWY_INLINE bool Compare1(const T* a, const T* b) const {
+    return AscBase().Compare1(b, a);
+  }
+  template <class D>
+  HWY_INLINE Mask<D> Compare(D d, Vec<D> a, Vec<D> b) const {
+    return AscBase().Compare(d, b, a);
+  }
+
+  template <class D>
+  HWY_INLINE Vec<D> First(D d, const Vec<D> a, const Vec<D> b) const {
+    return AscBase().Last(d, a, b);
+  }
+
+  template <class D>
+  HWY_INLINE Vec<D> Last(D d, const Vec<D> a, const Vec<D> b) const {
+    return AscBase().First(d, a, b);
+  }
+
+  template <class D>
+  HWY_INLINE Vec<D> FirstOfLanes(D d, Vec<D> v,
+                                 T* HWY_RESTRICT b) const {
+    return AscBase().LastOfLanes(d, v, b);
+  }
+
+  template <class D>
+  HWY_INLINE Vec<D> LastOfLanes(D d, Vec<D> v,
+                                T* HWY_RESTRICT b) const {
+    return AscBase().FirstOfLanes(d, v, b);
+  }
+
+  template <class D>
+  HWY_INLINE Vec<D> FirstValue(D d) const {
+    return AscBase().LastValue(d);
+  }
+
+  template <class D>
+  HWY_INLINE Vec<D> LastValue(D d) const {
+    return AscBase().FirstValue(d);
+  }
+
+  template <class D, class V = Vec<D>>
+  HWY_INLINE V PrevValue(D, V v) const {
+    return this->template NextSortValueBits<false>(v);
+  }
+};
+
+} // namespace detail
+}  // namespace HWY_NAMESPACE
+}  // namespace hwy
+HWY_AFTER_NAMESPACE();
+
+#endif  // HIGHWAY_HWY_CONTRIB_SORT_ORDER_EMULATE_TOGGLE

hwy/contrib/sort/sort_test.cc

@@ -61,17 +61,32 @@ using detail::OrderDescendingKV128;
 using detail::Traits128;
 #endif  // !HAVE_INTEL && HWY_TARGET != HWY_SCALAR
 
+template <typename T>
+inline void IotaWrapper(T *first, T *last, T val) {
+  std::iota(first, last, val);
+}
+// Emulate std::iota for hwy::float16_t, some compliers mostly on ARM & Longarch
+// complain about operator++ on that type.
+template <>
+inline void IotaWrapper<hwy::float16_t>(hwy::float16_t *first, hwy::float16_t *last, 
+                                        hwy::float16_t val) {
+  float v = ConvertScalarTo<float>(val);
+  for (; first != last; ++first, ++v) {
+    *first = ConvertScalarTo<hwy::float16_t>(v);
+  }
+}
+
 template <typename Key>
 void TestSortIota(hwy::ThreadPool& pool) {
   pool.Run(128, 300, [](uint64_t task, size_t /*thread*/) {
     const size_t num = static_cast<size_t>(task);
     Key keys[300];
-    std::iota(keys, keys + num, Key{0});
+    IotaWrapper(keys, keys + num, ConvertScalarTo<Key>(0));
     VQSort(keys, num, hwy::SortAscending());
     for (size_t i = 0; i < num; ++i) {
-      if (keys[i] != static_cast<Key>(i)) {
+      if (keys[i] != ConvertScalarTo<Key>(i)) {
         HWY_ABORT("num %zu i %zu: not iota, got %.0f\n", num, i,
-                  static_cast<double>(keys[i]));
+                  ConvertScalarTo<double>(keys[i]));
       }
     }
   });
@@ -86,10 +101,9 @@ void TestAllSortIota() {
     TestSortIota<int64_t>(pool);
     TestSortIota<uint64_t>(pool);
   }
+  TestSortIota<hwy::float16_t>(pool);
   TestSortIota<float>(pool);
-  if (hwy::HaveFloat64()) {
-    TestSortIota<double>(pool);
-  }
+  TestSortIota<double>(pool);
 #endif
 }