SIMD for eraseBetween (Node16)

ConflictSet.cpp

@@ -1773,22 +1773,60 @@ void eraseBetween(Node **inTree, Node3 *n, int begin, int end,
 
 void eraseBetween(Node **inTree, Node16 *n, int begin, int end,
                   WriteContext *tls) {
+  if (end - begin == 256) {
+    for (int i = 0; i < n->numChildren; ++i) {
+      eraseTree(n->children[i], tls);
+    }
+    n->numChildren = 0;
+    auto *newNode = tls->allocate<Node0>(n->partialKeyLen);
+    newNode->copyChildrenAndKeyFrom(*n);
+    tls->release(n);
+    *inTree = newNode;
+    return;
+  }
+  assert(end - begin < 256);
+
+#ifdef HAS_ARM_NEON
+  uint8x16_t indices;
+  memcpy(&indices, n->index, 16);
+  // 0xff for each in bounds
+  auto results =
+      vcltq_u8(vsubq_u8(indices, vdupq_n_u8(begin)), vdupq_n_u8(end - begin));
+  // 0xf for each 0xff
+  uint64_t mask = vget_lane_u64(
+      vreinterpret_u64_u8(vshrn_n_u16(vreinterpretq_u16_u8(results), 4)), 0);
+#elif defined(HAS_AVX)
+  __m128i indices;
+  memcpy(&indices, n->index, 16);
+  indices = _mm_sub_epi8(indices, _mm_set1_epi8(begin));
+  uint32_t mask = ~_mm_movemask_epi8(_mm_cmpeq_epi8(
+      indices, _mm_max_epu8(indices, _mm_set1_epi8(end - begin))));
+#else
   const unsigned shiftUpperBound = end - begin;
   const unsigned shiftAmount = begin;
   auto inBounds = [&](unsigned c) { return c - shiftAmount < shiftUpperBound; };
-  Node **nodeOut = n->children;
-  uint8_t *indexOut = n->index;
-  InternalVersionT *maxVOut = n->childMaxVersion;
-  for (int i = 0; i < n->numChildren; ++i) {
-    if (inBounds(n->index[i])) {
+  uint32_t mask = 0;
+  for (int i = 0; i < 16; ++i) {
+    mask |= inBounds(is[i]) << i;
+  }
+#endif
+  mask &= (decltype(mask)(1) << n->numChildren) - 1;
+
+  if (!mask) {
+    return;
+  }
+
+  int first = std::countr_zero(mask);
+  int count = std::popcount(mask);
+  n->numChildren -= count;
+  for (int i = first; i < first + count; ++i) {
     eraseTree(n->children[i], tls);
-    } else {
-      *nodeOut++ = n->children[i];
-      *indexOut++ = n->index[i];
-      *maxVOut++ = n->childMaxVersion[i];
   }
+  for (int i = first; i < n->numChildren; ++i) {
+    n->children[i] = n->children[i + count];
+    n->childMaxVersion[i] = n->childMaxVersion[i + count];
+    n->index[i] = n->index[i + count];
   }
-  n->numChildren = nodeOut - n->children;
 
   if (n->numChildren > Node3::kMaxNodes) {
     // nop